Grade Level

Alien Detector (Advanced)

Sunday March 7, 2010

This simple FET circuit is really an electronic version of the electroscope. This “Alien Detector” is a super-sensitive static charge detector made from a few electronics parts. I originally made a few of these and placed them in soap boxes and nailed the lids shut and asked kids how they worked. (I did place a on/off switch poking through the box along with the LED so they would have ‘some’ control over the experiment.)

This detector is so sensitive that you can go around your house and find pockets of static charge… even from your own footprints! This is an advanced project for advanced students.

You will need to get:

9V battery clip (and a 9V battery)
MPF 102 (buy 2 – one for back up)
LED (any regular LED works fine)

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Download Student Worksheet & Exercises

After you’ve made your charge detector, turn it on and comb your hair, holding the charge detector near your head and then the comb. You’ll notice that the comb makes the LED turn off, and your head (in certain spots) makes the LED go on. So it’s a positive charge static detector… this is important, because now you know when the LED is off, the space you’re detecting is negatively charged, and when it’s lit up, you’re in a pocket of positively charged particles. How far from the comb does your detector need to be to detect the charge? Does it matter how humid it is?

You can take your detector outdoors, away from any standing objects like trees, buildings, and people, and hold it high in the air. What does the LED look like? What happens when you lower the detector closer to the ground? Raise it back up again to get a second reading… did you find that the earth is negative, and the sky is more positive?

You can increase the antenna sensitivity by dangling an extra wire (like an alligator clip lead) to the end of the antenna. Because thunderstorms are moving electrical charges around (negative charges downwards and positive charges upwards), the earth is electrified negatively everywhere. During a thunderstorm, the friction caused by the moving water molecules is what causes lightning to strike! (But don’t test your ideas outside in the wide open while lightening is striking!)

Exercises

When the LED is on, what do you think it means?
Does the LED turning off detect anything?
Do aliens like humidity?
How does this alien detector really work?

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Simple Hovercraft

Wednesday February 10, 2010

Hovercraft transport people and their stuff across ice, grass, swamp, water, and land. Also known as the Air Cushioned Vehicle (ACV), these machines use air to greatly reduce the sliding friction between the bottom of the vehicle (the skirt) and the ground. This is a great example of how lubrication works – most people think of oil as the only way to reduce sliding friction, but gases work well if done right.

In this case, the readily-available air is shoved downward by the pressure inside of balloon. This air flows down through the nozzle and out the bottom, under the CD, lifting it slightly as it goes and creating a thin layer for the CD to float on.

Although this particular hovercraft only has a 'hovering' option, I'm sure you can quickly figure out how to add a 'thruster' to make it zoom down the table! (Hint - you will need to add a second balloon!)

Here's what you need:

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7-9" balloon
water bottle with a sport-top (see video for a visual - you can also use the top from liquid dish soap)
old CD
paper cup (or index card)
thumbtack
hot glue gun
razor with adult help

Download Student Worksheet here.

There's air surrounding us everywhere, all at the same pressure of 14.7 pounds per square inch (psi). You feel the same force on your skin whether you're on the ceiling or the floor, under the bed or in the shower. An interesting thing happens when you change a pocket of air pressure - things start to move.

This difference in pressure causes movement that creates winds, tornadoes, airplanes to fly, and the air to rush out of a full balloon. An important thing to remember is that higher pressure always pushes stuff around. While lower pressure does not "pull," we think of higher pressure as a "push".

The stretchy balloon has a higher pressure inside than the surrounding air, and the air is allowed to escape out the nozzle which is attached to the water bottle cap through tiny holes (so the whole balloon doesn't empty out all at once and flip over your hovercraft!) The steady stream of air flows under the CD and creates a cushion of air, raising the whole hovercraft up slightly... which makes the hovercraft easy to slide across a flat table.

Want to make an advanced model Hovercraft using wires, motors, and leftovers from lunch? Then click here.

[/am4show] [am4show have='p9;p39;' guest_error='Guest error message' user_error='User error message' ] Advanced students: Download your Hovercraft Lab here. [/am4show]

The Dark and Light of Polarization

Wednesday February 3, 2010

Polarization has to do with the direction of the light. Think of a white picket fence – the kind that has space between each board. The light can pass through the gaps int the fence but are blocked by the boards. That’s exactly what a polarizer does.

When you have two polarizers, you can rotate one of the ‘fences’ a quarter turn so that virtually no light can get through – only little bits here and there where the gaps line up. Most of the way is blocked, though, which is what happens when you rotate the two pairs of sunglasses. Your sunglasses are polarizing filters, meaning that they only let light of a certain direction in. The view through the sunglasses is a bit dimmer, as less photons reach your eyeball.

Polarizing sunglasses also reduce darken the sky, which gives you more contrast between light and dark, sharpening the images. Photographers use polarizing filters to cut out glaring reflections.

Materials:

two pairs of polarized sunglasses
tape (the 3/4″ glossy clear kind works best – watch second video below)
window

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Here’s what you do: Stack two pairs of sunglasses on top of each other and look through both sets of lenses… now rotate one pair a quarter turn (90^o). The lenses should block the light completely at 90^o and allow light to pass-through when aligned at 0^o. These lenses allow some light to pass through but not all. When you rotate the lenses to 90^o, you block out all visible light.

You use the “filter” principle in the kitchen. When you cook pasta, you use a filter (a strainer) to get the pasta out of the water. That’s what the sunglasses are doing – they are filtering out certain types of light. Rotating the lenses 90^o to block out all light is like trying to strain your pasta with a mixing bowl. You don’t allow anything to pass through.

Astronomers use polarizing filters to look at the moon. Ever notice how bright the moon is during a full moon, and how dim it is near new moon? Using a rotating polarizing filter, astronomer can adjust the amount of light that enters into their eye.

Download Student Worksheet & Exercises

Advanced students: Download your Polarization lab here.

Exercises

Why do you need two polarizers to block the light completely?
How can you tell if your sunglasses are polarized if you only have one pair?

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How to “See” Infra-Red Light

Wednesday February 3, 2010

Crazy Remote

Want to have some quick science fun with your TV remote? Then try this experiment next time you flip on the tube:

Materials:

metal frying pan or cookie sheet
TV remote control
plastic sheet

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Making IR Visible to the Human Eye

Infra-red light is in the part of the electromagnetic spectrum that isn’t usually visible to human eyes, but using this nifty trick, you will easily be able to see the IR signal from your TV remote, remote-controller for an RC car, and more!

TV remote control
camera (video or still camera)

Download Student Worksheet & Exercises

Exercises

Look over your data table. What kinds of objects (plastic, metal, natural, etc.) allow infrared light to pass through them?
Why does the camera work in making the infrared light visible?

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Light Tricks

Wednesday February 3, 2010

When light rays strikes a surface, part of the beam passes through the surface and the rest reflects back, like a ball bouncing on the ground. Where it bounces depends on how you throw the ball.

Have you ever looked into a pool of clear, still water and seen your own face? The surface of the water acts like a mirror and you can see your reflection. (In fact, before mirrors were invented, this was the only way people had to look at themselves.) If you were swimming below the surface, you’d still see your own face – the mirror effect works both ways.

Have you ever broken a pencil by sticking it into a glass of water? The pencil isn’t really broken, but it sure looks like it! What’s going on?

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When a beam of light hits a different substance (like the water), the wavelength changes because the speed of the light changes. If you’re thinking that the speed of light is always constant, you’re right… in a vacuum like outer space between two reference frames.

But here on Earth, we can change the speed of light just by shining a light beam through different materials, like water, ice, blue sunglasses, smoke, fog, even our own atmosphere. How much the light speed slows down depends on what the material is made of. Mineral oil and window glass will slow light down more than water, but not as much as diamonds do.

How broken the pencil appears also depends on where you look. In some cases, you’ll see a perfectly intact pencil. Other times, you’ll guess neither piece is touching. This is why not everyone can see a rainbow after it rains. The sun must be at a low angle in the sky, and also behind you for a rainbow to appear. Most times, you aren’t at the right spot to see the entire arc touch the ground at both ends, either.

Lenses work to bend light the way you want them to. The simplest lenses are actually prisms. Prisms unmix light into its different wavelengths. When light hits the prism, most of it passes through (a bit does reflect back) and changes speed. Since the sunlight is made up of many different wavelengths (colors), each color gets bent by different amounts, and you see a rainbow out the other side.

Double Your Money

Here are a few neat activities that experiment with bending light, doubling your money, and breaking objects. Here’s what you do:

Materials:

glass jar (or water glass)
penny
eyeballs

Download Student Worksheet & Exercises

Here’s what you do:

1. Toss one coin into a water glass (pickle jars work great) and fill with an inch of water. Hold the glass up and find where you need to look to see TWO coins. Are the coins both the same size? Which one is the original coin? (Answer at the bottom of this page.)

2. Look through the top of the glass – how many coins are there now? What about when you look from the side?

3. Toss in a second coin – now how many are there?

4. Remove the coins turn out the lights. Shine a flashlight beam through the glass onto a nearby wall. (Hint – if this doesn’t work, try using a square clear container.) Stick a piece of paper on the wall where your light beam is and outline the beam with a pencil.

5. Shine the light at an angle up through the water so that it bounces off the surface of the water from underneath. Trace your new outline and compare… are they both the same shape?

6. Add a teaspoon of milk and stir gently. (No milk? Try sprinkling in a bit of white flour.) Now shine your flashlight through the container as you did in steps 4 and 5 and notice how the beam looks.

7. Use a round container instead of square… what’s the difference?

Answers:
1. The smaller coin is the reflection.
2. One coin when glanced from above, two from the side.
3. Four.
4. Beam is a circle.
5. Beam is an oval.
6. I can see the beam through the water!!
7. The round container distorts the beam, and the square container keeps the light beam straight. Both are fun!

The coin water trick is a neat way for kids to see how refraction works. In optics, refraction happens when light waves travel from one medium with a certain refractive index (air, for example) to another medium which has a different refractive index (like water). At the boundary between the two (where air meets water), the wave changes direction.

The wavelength increases or decreases but the frequency remains constant. When you sine light through a prism, the wavelength changes and you see a rainbow as the prism un-mixes white light into its different colors.The light wave changed direction when it traveled from air to glass, and then back to air again as it leaves the backside of the prism.

Did you try the pencil experiment? Did you notice how if you look at the pencil (placed at a slant) partially in the water, it appears to bend at the water’s surface? The light waves bend as they travel from water to air. To further complicate things, the way the eye received information about the position of the pencil actually makes the pencil to appear higher and the water shallower than they really are! Can you imagine how important this is for trying to spear a fish? The fish might appear to be in a different place, so you need to account for this when you take aim!

Click here for the Disappearing Beaker experiment!

Exercises

When one coin is in the water, you can actually see two: Are the coins both the same size? Which one is the original coin?
In step 2 of the experiment: How many coins are there when viewed from the top of the glass? What about when you look from the side?
What happened when you tossed in a second coin?
How did your outlines compare?

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Disappearing Beaker

Wednesday February 3, 2010

We’re going to bend light to make objects disappear. You’ll need two glass containers (one that fits inside the other), and the smaller one MUST be Pyrex. It’s okay if your Pyrex glass has markings on the side. Use cooking oil such as canola oil, olive oil, or others to see which makes yours truly disappear. You can also try mineral oil or Karo syrup, although these tend to be more sensitive to temperature and aren’t as evenly matched with the Pyrex as the first choices mentioned above.

Here’s what you need:

two glass containers, one of which MUST be Pyrex glass
vegetable oil (cheap canola brand is what we used in the video)
sink

Published value for light speed is 299,792,458 m/s = 186,282 miles/second = 670,616,629 mph
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When a beam of light hits a different substance (like glass), the speed of light changes. The color of the light (called the wavelength) can also change. In some cases, the change of wavelength turns into a change in the direction of the beam.

For example, if you stick a pencil is a glass of water and look through the side of the glass, you’ll notice that the pencil appears shifted. The speed of light is slower in the water (140,000 miles per second) than in the air (186,000 miles per second), called optical density, and the result is bent light beams and broken pencils.

You’ll notice that the pencil doesn’t always appear broken. Depending on where your eyeballs are, you can see an intact or broken pencil.

This is a very fine point about refraction: when light enters a new substance (like going from air to water) perpendicular to the surface (looking straight on), refractions do not occur.

However, if you look at the glass at an angle, then depending on your sight angle, you’ll see a different amount of shift in the pencil. Where do you need to look to see the greatest shift in the two halves of the pencil? (Hint: move the pencil back and forth slowly.)

Depending on if the light is going from a lighter to an optically denser material (or vice versa), it will bend different amounts. Glass is optically denser than water, which is denser than air.

Here’s a chart:

Vacuum 1.0000
Air 1.0003
Ice 1.3100
Water 1.3333
Pyrex 1.4740
Cooking Oil 1.4740
Diamond 2.4170

This means if you place a Pyrex container inside a beaker of vegetable oil, it will disappear. This also works for some mineral oils and Karo syrup. Note however that the optical densities of liquids vary with temperature and concentration, and manufacturers are not perfectly consistent when they whip up a batch of this stuff, so some adjustments are needed.

Not only can you change the shape of objects by bending light (broken or whole), but you can also change the size. Magnifying lenses, telescopes, and microscopes use this idea to make objects appear different sizes.

Questions to Ask

Does the temperature of the oil matter?
What other kinds of oil work? Blends of oils?
Does it work with mineral oil or Karo syrup?
Is there a viewing angle that makes the inside container visible?
Which type of lighting makes the container more invisible?
Can we see light waves?

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Microscopes and Telescopes

Wednesday February 3, 2010

Hans Lippershey was the first to peek through his invention of the refractor telescope in 1608, followed closely by Galileo (although Galileo used his telescope for astronomy and Lippershey’s was used for military purposes). Their telescopes used both convex and concave lenses.

A few years later, Kepler swung into the field and added his own ideas: he used two convex lenses (just like the ones in a hand-held magnifier), and his design the one we still use today. We're going to make a simple microscope and telescope using two lenses, the same way Kepler did. Only our lenses today are much better quality than the ones he had back then!

You can tell a convex from a concave lens by running your fingers gently over the surface – do you feel a “bump” in the middle of your hand magnifying lens? You can also gently lay the edge of a business card (which is very straight and softer than a ruler) on the lens to see how it doesn't lay flat against the lens.

Your magnifier has a convex lens – meaning the glass (or plastic) is thicker in the center than around the edges. The image here shows how a convex lens can turn light to a new direction using refraction. You can read more about refraction here.

A microscope is very similar to the refractor telescope with one simple difference – where you place the focus point. Instead of bombarding you with words, let’s make a microscope right now so you can see for yourself how it all works together. Are you ready?

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How to Make a Microscope

Materials:

2 hand held magnifiers
dollar bill
penny - Note: The penny used in this video shows the Lincoln Memorial, which was shown on pennies minted between 1959 - 2008.

Here's what you do: Hold one magnifying glass in each hand. Focus one lens on a printed letter or small object. Add the second lens above the first, so you can see through both. Move the lens toward and away from you until you bring the letter into clear focus again. You just made a microscope! The lens closest to your eye is the EYEpiece. The lens closest to the object is the OBJECTive. The image here is of the objective part of a compound microscope. The different silver tubes have different sizes of lenses, each with a different magnification, so the same scope can go from 40X to 1,000X with the flip of a lens.

How do I determine magnification power for my microscope? Simply multiply the powers of your optics together to get the power of magnification. If you’re using one lens at 10X and the other at 4X, then the combined effect is 40X. You’ll usually find the power rating stamped in tiny writing along the magnifier.

So now you've made a microscope. How about a telescope? Is it really a lot different?

The answer is no. Simply hold your two lenses as you would for a microscope, but focus on a far-away object like a tree. You just made a simple telescope… but the image is upside-down!

microscope1 We don’t fully understand why, but every time we teach this class, kids inevitably start catching things on fire. We think it’s because they want to see if they really can do it – and sure enough, they find out that they can! Just do it in a safe spot (like a leaf on concrete) if that’s something you want to do. Click here for a detailed instructional video on how to do this safely.

How do I connect the flaming shrubbery back to the main optics lesson? Ask your child why the leaf catches on fire… and when the shrug, you can lead them around to a discussion about focus points of a lens. It’s hard for kids to visualize the light lines through a lens, so you can shine a strong light through a fine-tooth comb as shown in the image above. Use clear gelatin (or Jell-O) shapes as your “lenses” and shine your rays of light through it. If your room is dark enough, you’ll get the image shown above.

The point where all the lines intersect is where things catch fire, as the energy is most concentrated at this point. Note how the lines flip after the focus point – this is why the telescope images are inverted. The microscope image is not flipped because you’ve placed the image (and/or your eye) before the focus point. Play around with it and find out where the focus point is. Slide your lenses along a yardstick to easily measure distances.

How to Make a Telescope

Materials:

2 hand held magnifiers
window

Want to experiment further? Then click for the Optical Bench experiment and also sneak a peek at the Advanced Telescope Building experiment where you will learn about lenses, refractor, and newtonian telescopes.

Ready to buy your own professional-quality instrument that will last you all the way through college? Click here for our recommendations on microscopes, telescopes, and binoculars.
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Spectrometer

Wednesday February 3, 2010

Spectrometers are used in chemistry and astronomy to measure light. In astronomy, we can find out about distant stars without ever traveling to them, because we can split the incoming light from the stars into their colors (or energies) and “read” what they are made up of (what gases they are burning) and thus determine their what they are made of. In this experiment, you’ll make a simple cardboard spectrometer that will be able to detect all kinds of interesting things!

SPECIAL NOTE: This instrument is NOT for looking at the sun. Do NOT look directly at the sun. But you can point the tube at a sheet of paper that has the sun’s reflected light on it.

Usually you need a specialized piece of material called a diffraction grating to make this instrument work, but instead of buying a fancy one, why not use one from around your house? Diffraction gratings are found in insect (including butterfly) wings, bird feathers, and plant leaves. While I don’t recommend using living things for this experiment, I do suggest using an old CD.

CDs are like a mirror with circular tracks that are very close together. The light is spread into a spectrum when it hits the tracks, and each color bends a little more than the last. To see the rainbow spectrum, you’ve got to adjust the CD and the position of your eye so the angles line up correctly (actually, the angles are perpendicular).

You’re looking for a spectrum (the rainbow image at left) – this is what you’ll see right on the CD itself. Depending on what you look at (neon signs, chandeliers, incandescent bulbs, fluorescent bulbs, Christmas lights…), you’ll see different colors of the rainbow. For more about how diffraction gratings work, click here.

Materials:

old CD
razor
index card
cardboard tube

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Download Student Worksheet & Exercises

Find an old CD and a cardboard tube at least 10 inches long. Cut a clean slit less than 1 mm wide in an index card or spare piece of cardboard and tape it to one end of the tube. Align your tube with the slit horizontally, and on the top of the tube at the far end cut a viewing slot about one inch long and ½” inch wide. Cut a second slot into the tube at a 45 degree angle from the vertical away from the viewing slot. Insert the CD into this slot so that it reflects light coming through the slit into your eye (viewing slot).

Aim the 1 mm slit at a light source such as a fluorescent light, neon sign, sunset, light bulb, computer screen, television, night light, candle, fireplace… any light source you can find. Look through the open hole at the light reflected off the compact disk (look for a rainbow in most cases) inside the cardboard tube.

Troubleshooting: This is a quick and easy way to bypass the need for an expensive diffraction grating. Use your spectrometer to look at computer screens, laptops, night lights, neon lights, candles, campfires, fluorescent lights, incandescent lights, LEDs, stoplights, street lights, and any other light sources you can find, even the moon through a telescope.

To make a CALIBRATED Spectrometer, go here.

Exercises

Name three more light sources that you think might work with your spectroscope.
Why is there a slit at the end of the tube instead of leaving it open?

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Pinhole Camera

Wednesday February 3, 2010

This is the simplest form of camera – no film, no batteries, and no moving parts that can break. The biggest problem with this camera is that the inlet hole is so tiny that it lets in such a small amount of light and makes a faint image. If you make the hole larger, you get a brighter image, but it’s much less focused. The more light rays coming through, the more they spread out the image out more and create a fuzzier picture. You’ll need to play with the size of the hole to get the best image.

While you can go crazy and take actual photos with this camera by sticking on a piece of undeveloped black and white film (use a moderately fast ASA rating), I recommend using tracing paper and a set of eyeballs to view your images. Here’s what you need to do:

Materials:

box
tracing paper
razor or scissors
tape
tack

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Download Student Worksheet & Exercises

Here’s the quick set of instructions:

1. Use a cardboard box that is light-proof (no leaks of light anywhere).
2. Seal light leaks with tape if you have to. Cut off one side of the box (Note – there’s no need to do this if you’re using a shoebox).
3. Tape a piece of tracing paper over the cutout side, keeping it taut and smooth.
4. Make a pinhole in the box side opposite of the tracing paper.
5. Point the pinhole at a window and move toward or away from the window until you see its image in clear focus on the tracing paper.

OPTIONAL: You can hold up a magnifying glass in front of the pinhole to sharpen the image.

Exercises

How do the images appear when they’re projected onto the paper inside your camera?
Why do you think it’s important to make the box as light-proof as possible?
Is there a part of your body that works similarly to the pinhole?
Sketch a picture of something you saw through your pinhole camera.

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Mixing Cold Light

Wednesday February 3, 2010

Here’s a trick question – can you make the color “yellow” with only red, green, and blue as your color palette? If you’re a scientist, it’s not a problem. But if you’re an artist, you’re in trouble already.

The key is that we would be mixing light, not paint. Mixing the three primary colors of light gives white light. If you took three light bulbs (red, green, and blue) and shined them on the ceiling, you’d see white. And if you could magically un-mix the white colors, you’d get the rainbow (which is exactly what prisms do.)

If you’re thinking yellow should be a primary color – it is a primary color, but only in the artist’s world. Yellow paint is a primary color for painters, but yellow light is actually made from red and green light. (Easy way to remember this: think of Christmas colors – red and green merge to make the yellow star on top of the tree.)

As a painter, you know that when you mix three cups of red, green, and blue paint, you get a muddy brown. But as a scientist, when you mix together three cups of cold light, you get white. If you pass a beam white light through a glass filled with water that’s been dyed red, you’ve now got red light coming out the other side. The glass of red water is your filter. But what happens when you try to mix the different colors together?

The cold light is giving off its own light through a chemical reaction called chemiluminescence, whereas the cups of paint are only reflecting nearby light. It’s like the difference between the sun (which gives off its own light) and the moon (which you see only when sunlight bounces off it to your eyeballs). You can read more about light in our Unit 9: Lesson 1 section.

Here’s what you need:

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disposable clear plastic cup or glass jar
one of each: red, green, and blue true-color light sticks (Order true color glow sticks here.)
scissors with adult help
sink

Download Student Worksheet & Exercises

You can demonstrate the primary colors of light using glow sticks! When red, green, and blue cold light are mixed, you get white light.

Simply activate the light stick (bend it until you hear a *crack* – that’s the little glass capsule inside breaking) and while wearing gloves, carefully slice off one end of the tube with strong cutters, being careful not to splash (do this over a sink).

Cut off the ends for all three light sticks. Pass the contents of the light sticks through a coffee filter (or paper towel) into a disposable cup – this will capture the glass bits. Now your cup should be glowing white.

Sometimes the chemical light sticks contain a glowing green liquid encapsulated within a red or blue plastic tube, so when you slice it open to combine it with the other colors, it isn’t a true red. Be sure that your chemical light sticks contain a glowing RED LIQUID and BLUE LIQUID in a clear, colorless plastic tube, or this experiment won’t work. Order true color glow sticks here.

Exercises

What color do you get when you mix blue and green liquid lights?
What happens when you start to add the red light?
What is your final color result when mixing red, blue, and green lights?
How would your result differ if you instead mixed red, blue and green paints?

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Measuring the Speed of Light with a Chocolate Bar

Wednesday February 3, 2010

When you warm up leftovers, have you ever wondered why the microwave heats the food and not the plate? (Well, some plates, anyway.) It has to do with the way microwave ovens work.

Microwave ovens use dielectric heating (or high frequency heating) to heat your food. Basically, the microwave oven shoots light beams that are tuned to excite the water molecule. Foods that contain water will step up a notch in energy levels as heat. (The microwave radiation can also excite other polarized molecules in addition to the water molecule, which is why some plates also get hot.)

One of the biggest challenges with measuring the speed of light is that the photons move fast… too fast to watch with our eyeballs. So instead, we’re going to watch the effects of microwave light and base our measurements on the effects the light has on different kinds of food. Microwaves use light with a wavelength of 0.01 to 10 cm (that’s ‘microwave’ part of the electromagnetic spectrum). When designing your experiment, you’ll need to pay close attention to the finer details such as the frequency of your microwave oven (found inside the door), where you place your food inside the oven, and how long you leave it in for.

Materials:

chocolate bar (extra-large bars work best)
microwave
plate
ruler
calculator
pencil and paper

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Download Student Worksheet & Exercises

First, you’ll need to find the ‘hot spots’ in your microwave. Remove the turntable from your microwave and place a naked bar of chocolate on a plate inside the microwave. Make sure the chocolate bar is the BIG size – you’ll need at least 7 inches of chocolate for this to work. Turn the microwave on and wait a few minutes until you see small parts of the chocolate bar start to bubble up, and then quickly open the door (it will start to smoke if you leave it in too long). Look carefully at the chocolate bar without touching the surface… you are looking for TWO hotspots, not just one – they will look like small volcano eruptions on the surface of the bar. If you don’t have two, grab a fresh plate (you can reuse the chocolate bar) and try again, changing the location of the place inside the microwave. You’re looking for the place where the microwave light hits the chocolate bar in two spots so you can measure the distance between the spots. Those places are the places where the microwave light wave hits the chocolate.

Open up the door or look on the back of your microwave for the technical specifications. You’re looking for a frequency in the 2,000-3,000 MHz range, usually about 2450 MHz. Write this number down on a sheet of paper – this tells you the microwave radiation frequency that the oven produces, and will be used for calculating the speed of light. (Be sure to run your experiment a few times before taking actual data, to be sure you’ve got everything running smoothly. Have someone snap a photo of you getting ready to test, just for fun!)

When you’re ready, pop in the first food type on a plate (without the turntable!) into the best spot in the microwave, and turn it on. Remove when both hotspots form, and being careful not to touch the surface of the food, measure the center-to-center distance using your ruler in centimeters.

TIP: If you’re using mini-marshmallows or chocolate chips (or other smaller foods), you’ll need to spread them out in an even layer on your plate so you don’t miss a spot that could be your hotspot!

How to Calculate the Speed of Light from your Data

Note that when you measure the distance between the hotspots, you are only measuring the peak-to-peak distance of the wave… which means you’re only measuring half of the wave. We’ll multiply this number by two to get the actual length of the wave (wavelength). If you’re using centimeters, you’ll also need to convert those to meters by dividing by 100.

So, if you measure 6.2 cm between your hotspots, and you want to calculate the speed of light and compare to the published value which is in meters per second, here’s what you do:

2,450 MHz is really 2,450,000,000 Hz or 2,450,000,000 cycles per 1 second

Find the length of the wave (in cm): 2 * 6.2 cm = (12.4 cm) /(100 cm/m) = 0.124 meters

Multiply the wavelength by the microwave oven frequency:

0.124 m * 2,450,000,000 Hz = 303,800,000 m/s

Published value for light speed is 299,792,458 m/s = 186,282 miles/second = 670,616,629 mph

Click here to learn how to turn this project into a Science Fair Project you can enter!

Exercises

What would happen if you used cheese instead of chocolate?
Does it matter where in the microwave the chocolate is located? Does placement of the chocolate affect the wavelength?
Can you explain what the burn marks on the chocolate bar are from?

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Rainbow Shadows

Wednesday February 3, 2010

Imagine you’re a painter. What three colors do you need to make up any color in the universe? (You should be thinking: red, yellow, and blue… and yes, you are right if you’re thinking that the real primary colors are cyan, magenta, and yellow, but some folks still prefer to think of the primary colors as red-yellow-blue… either way, it’s really not important to this experiment which primary set you choose.)

Here’s a trick question – can you make the color “yellow” with only red, green, and blue as your color palette? If you’re a scientist, it’s not a problem. But if you’re an artist, you’re in trouble already.

The key is that we would be mixing light, not paint. Mixing the three primary colors of light gives white light. If you took three light bulbs (red, green, and blue) and shined them on the ceiling, you’d see white. And if you could magically un-mix the white colors, you’d get the rainbow (which is exactly what prisms do.)

If you’re thinking yellow should be a primary color – it is a primary color, but only in the artist’s world. Yellow paint is a primary color for painters, but yellow light is actually made from red and green light. (Easy way to remember this: think of Christmas colors – red and green merge to make the yellow star on top of the tree.) It’s because you are using projection of light, not the subtrative combination of colors to get this result.

Here’s a nifty experiment that will really bring these ideas to life (and light!):

Materials:

flashlight (three is best, but you can get by with two)
fingernail polish (red, green, and blue)
clear tape or cellophane (saran wrap works too)
white wall space

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Download Student Worksheet & Exercises

Here’s what you do: Find three flashlights. Cover each with colored cellophane (color filters) or paint the plastic lens cover with nail polish (red, green, and blue). Shine onto a white ceiling or wall, overlap the colors and make new colors. Leave the flashlights on, line them up on a table, turn off the lights, and dance – you will be making rainbow shadows on the wall! In addition, you can paint the lens of a fourth flashlight yellow to see what happens.

When you combine red and green light, you will get yellow light. Combine green and blue to get cyan (turquoise). Combine blue and red to get magenta (purple). Turn on the red and green lights and the wall will appear yellow. Wave your hand in front of the lights and you will see cyan and magenta shadows. Turn on the green and blue lights, and the wall turns cyan with yellow and magenta shadows. Turning on the blue and red give a magenta wall with yellow and cyan shadows. Turn on all colors and you will get a white wall with cyan, yellow, and magenta shadows – rainbow shadows!

Troubleshooting: This experiment has a few things to be aware of. If you’re not getting the colored shadows, check to be sure that the flashlight is bright enough to illuminate a wall in the dark. Be sure to shut the doors, shades, windows, and drapes. In the dark, when you shine your red flashlight on the wall, the wall should glow red. Beware of using off-color nail polish – make sure it’s really red, not hot pink.

If you still need help making this experiment work, you can visit your local hardware store and find three flood lamp holders (the cheap clamp-style ones made from aluminum work well – you’ll need three) and screw in colored “party lights” (make one red, one green, and one blue), which are colored incandescent bulbs. These will provide a lot more light! You can also add a fourth yellow light to further illustrate how yellow light isn’t a primary color. Try using only red, yellow, and blue… you’ll quickly find that you can’t obtain all the colors as you could with the original red-green-blue lights.

Exercises

What are the three primary colors of light?
What color do you get when mixing the primary colors of light?
How do you mix the primary colors of light to get yellow?
Use crayons or colored pencils to draw what you saw when all three lights were shining on the wall and you waved your hand in front of the light.

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Light, Lasers, and Optics

Wednesday February 3, 2010

When I was in grad school, I needed to use an optical bench to see invisible things. I was trying to ‘see’ the exhaust from a new kind of F15 engine, because the aircraft acting the way it shouldn’t – when the pilot turned the controls 20^o left, the plane only went 10^o. My team had traced the problem to an issue with the shock waves, and it was my job to figure out what the trouble was. (Anytime shock waves appear, there’s an energy loss.)

Since shock waves are invisible to the human eye, I had to find a way to make them visible so we could get a better look at what was going on. It was like trying to see the smoke generated by a candle – you know it’s there, but you just can’t see it. I wound up using a special type of photography called Schlieren.

An optical table gives you a solid surface to work on and nails down your parts so they don’t move. This is an image taken with Schlieren photography. This technique picks up the changes in air density (which is a measure of pressure and volume).

The air above a candle heats up and expands (increases volume), floating upwards as you see here. The Schlieren technique shines a super-bright xenon arc lamp beam of light through the candle area, bounces it off two parabolic mirrors and passes it through a razor-edge slit and a neutral density filter before reaching the camera lens. With so many parts, I needed space to bolt things down EXACTLY where I wanted them. The razor slit, for example, just couldn’t be anywhere along the beam – it had to be right at the exact point where the beam was focused down to a point.

I’m going to show you how to make a quick and easy optical lab bench to work with your lenses. Scientists use optical benches when they design microscopes, telescopes, and other optical equipment. You’ll need a bright light source like a flashlight or a sunny window, although this bench is so light and portable that you can move it to garage and use a car headlight if you really want to get creative. Once your bench is set up, you can easily switch out filters, lenses, and slits to find the best combination for your optical designs. Technically, our setup is called an optical rail, and the neat thing about it is that it comes with a handy measuring device so you can see where the focal points are for your lenses. Let’s get started:
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Materials:

lenses (glass or plastic), magnifying lenses work also
two razor blades (new)
index cards (about four)
razor
old piece of wood
single hair from your head
tape
aluminum foil
clothespins (2-4)
laser pointer
popsicle sticks (tongue-depressor size)
hot glue gun
scissors and a sharp razor
meter sticks (2)
bright light source (ideas for this are on the video)

Your lenses are curved pieces of glass or plastic designed to bend (refract) light. A simple lens is just one piece, and a compound lens is like the lens of a camera – there’s lots of them in there. The first lenses were developed by nature – dewdrops on plant leaves are natural lenses. The light changes speed and bends when it hits the surface of the drop, and things under the drop appear larger. (Read more about refraction here.) The earliest written records of lenses are found in the Greek archives and described as being glass globes filled with water.

Concave Lenses

Concave lenses are shaped like a ‘cave’ and curve inward like a spoon. Light that shines through a concave lens bends to a point (converging beam). Ever notice how when you peep through the hole in a door (especially in a hotel), you can see the entire person standing on the doorstep? There’s a concave lens in there making the person appear smaller.

You’ll also find these types of lenses in ‘shoplifting mirrors’. Store owners post these mirrors around help them see a larger area than a flat mirror shows, although the images tend to be a lot smaller.

If you have a pair of near-sighted glasses, chances are that the lenses are concave. Near-sighted folks need help seeing things that are far away, and the concave lenses increase the focal point to the right spot on their retina.

Concave lenses work to make things look smaller, so there not as widely used as convex lenses. You’ll find concave lenses inside camera lenses and binoculars to help clear weird optical problems that happen around the edges of a convex lens (called aberration).

Here’s a video on lenses, both convex and concave:

Convex lenses bulge outwards, bending the light out in a spray (diverging beam). A hand-held magnifying glass is a single concave lens with a handle. These lenses have been used as ‘burning glasses’ for hundreds of years – by placing a small piece of paper at its focal point and using the sun as a light source, you can focus the light energy so intensely that you reach the flash point of the paper (the paper auto-ignites around 450^oF).

When you stack a large convex lens above a solar panel, the magnification effect makes it so you can get away with using a smaller photovoltaic cell to get the same amount of energy from the sun. You’ll find convex lenses in telescopes, microscopes, binoculars, eyeglasses, and more.

Mirrors

What if you coat one side of the lens with a reflecting silver coating? You get a mirror!

Stick wooden skewers into a piece of foam to simulate how the light rays reflect off the surface of the mirror. Note that when the mirror (foam) is straight, the light rays are straight (which is what you see when you look in the bathroom mirror). The light bounces off the straight mirror and zips right back at you, remaining parallel.

Now arch the foam. Notice how the light ways (skewers) come to a point (focal point).

After the focal point, the rays invert, so the top skewer is now at the bottom and the bottom is now at the top. This is your flipped (inverted) image. This is what you’d see when you look into a concave mirror, like the inside of a metal spoon. You can see your face, but it’s upside-down.

Slits

A slit allows light from only one source to enter. If you have light from other sources, your light beam is more scattered and your images and lines become blurry. Thin slits can be easily made by placing the edges of two razor blades very close together and securing into place. We’re going to use an anti-slit using a piece of hair, but you can substitute a thin needle.

Here’s a video on using filters and slits with your laser:

Filters

There are hundreds of different types of filters, used in photography, astronomy, and sunglasses. A filter can change the amount and type of light allowed through it. For example, if you put on red-tinted glasses, suddenly everything takes on a reddish hue. The red filter blocks the rest of the incoming wavelengths (colors) and only allows the red colors to get to your eyeball. There are color filters for every wavelength, even IR and UV.

UV filters reduce the haziness in our atmosphere, and are used on most high-end camera lenses, while IR filters are heat-absorbing filters used with hot light sources (like near incandescent bulbs or in overhead projectors).

A neutral density (ND) filter is a grayish-colored filter that reduces the intensity of all colors equally. Photographers use these filters to get motion blur effects with slow shutter speeds, like a softened waterfall.

Build an Optical Bench

It’s time to put all these pieces together and make cool optical stuff – are you ready?

Download Student Worksheet & Exercises

Click here for more experiments on building your own microscope and telescope.

Cat’s Eyes

Corner reflectors are U-turns for light beams. A corner mirror made from three mirrors will reflect the beam straight back where it came from, no matter what angle you hit it at. Astronauts placed these types of mirrors on the moon so scientists could easily bounce laser beams off the moon and have them return to the same place on Earth. They used these reflected laser beams to measure the speed of light.

You’ll find corner mirrors in “cat’s eye” reflectors on the road. Car headlights illuminate the reflectors and send the beam straight back the same way – right at the driver.

Exercises

Using only the shape, how can you tell the difference between a convex and a concave lens?
Which type of lens makes objects viewed through it appear smaller?
Which type of lens makes the objects viewed through it appear larger?
How do you get the f number?

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Benham’s Disk

Wednesday February 3, 2010

Charles Benhamho (1895) created a toy top painted with the pattern (images on next page). When you spin the disk, arcs of color (called “pattern induced flicker colors”) show up around the disk. And different people see different colors!

We can’t really say why this happens, but there are a few interesting theories. Your eyeball has two different ways of seeing light: cones and rods. Cones are used for color vision and for seeing bright light, and there are three types of cones (red, green, and blue). Rods are important for seeing in low light.

One possibility is… [am4show have=’p8;p9;p19;p46;p66;’ guest_error=’Guest error message’ user_error=’User error message’ ]

…how the human eye is tuned for different colors. Your eyeballs respond at different rates to red, green, and blue colors. The spinning disk triggers different parts of the retina. This alternating response may cause some type of interaction within the nervous system that generates colors.

Another theory is that certain cones take longer react, and thus stay active, for longer amounts of time (though we’re still talking milliseconds, here). To put another way, the white color activates all three cones, but then the black deactivates them in a certain sequence, causing your brain to get mixed and unbalanced signals. Your brain does the best it can to figure it out the information it’s getting, and “creates” the colors you see in order to make sense of it all.

Neither of these theories explains the colors of Benham’s disk completely and the reason behind the illusion remains unsolved. Can you help out these baffled scientists?

Materials:

Download this PDF file
string (about 3 feet)

Download Student Worksheets & Exercises

All you need to do is download this PDF file and cutout a copy of a disc on the page. Then find a way to spin it at high speeds – you can stick a pencil through the center and spin it like a top, thread string through it and pull to rotate (just like the Mixing Colors Experiment), attach to a drill or mixer or electric screwdriver, or slap it on a motor shaft and engage the power. Which works best?

Exercises

What colors were you able to see when the disks were spinning?
How did the different patterns look when they were spun?
How did speed and direction affect what you saw?

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Liquid Prism

Wednesday February 3, 2010

In this experiment, water is our prism. A prism un-mixes light back into its original colors of red, green, and blue. You can make prisms out of glass, plastic, water, oil, or anything else you can think of that allows light to zip through.

What’s a prism? Think of a beam of light. It zooms fast on a straight path, until it hits something (like a water drop). As the light goes through the water drop, it changes speed (refraction). The speed change depends on the angle that the light hits the water, and what the drop is made of. (If it was a drop of mineral oil, the light would slow down a bit more.) Okay, so when white light passes through a prism (or water drop), changes speed, and turns colors. So why do we see a rainbow, not just one color coming out the other side?

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The secret is because the light is made up of different wavelengths, and each gets bent by different amounts when they hit a new material. So one wave changes speed to red, another to yellow, another to green, etc. when the beam hits the prism. And water drops are tiny prisms.

The light passing through a water drop gets refracted twice, not once. The first time is when it enters the water drop, the second when it bounces off the other side of the drop and reflects back through the water drop and out again (some of the light does make it out the other side of the drop, but most of it bounces back). When the light emerges from the water drop, it changes speed again, and presto! You have a rainbow.

Natural rainbows (the ones that you see after it rains) happen when water drops (tiny prisms) in the air are hit by sunlight from behind you at just the right angle (which is relatively a low angle, near the ground). The best rainbows can be seen when half of the sky is darkened with rainclouds and you’re in a clear patch with sun behind you. And guess what? You can even see a nighttime rainbow (called a moonbow), although they’re pretty rare, usually near full moon.

Here’s what you do:

Materials:

mirror
shallow baking dish
water
sunlight

Download Student Worksheet & Exercises

Set a clear tray of water in sunlight. Lean a mirror against an inside edge and adjust so that a rainbow appears on the wall. You can also use a light bulb shining through a slit in a flat cardboard piece as a light source.

Troubleshooting: This is one of the easiest experiments to do, and the most beautiful. The trouble is, you don’t know where the water shadow will show up, so make sure you point the mirror to the sky and play with the angle of the mirror until you find the wavering rainbow. Because the shadow is constantly moving, you can snap a few pictures when you’ve got it so you can look over the finer details later. If this project still eludes you, take a large sheet and use it instead of the tiny index card.

Exercises

What serves as the prism in this experiment?
What property can help make something a good prism material?
What are some other items that could be used as prisms?

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Kaleidoscopes

Wednesday February 3, 2010

In a simplest sense, a kaleidoscope is a tube lined with mirrors. Whether you leave the end opened or tape on a bag of beads is up to you, but the main idea is to provide enough of an optical illusion to wow your friends. Did you know that by changing the shape and size of the mirrors, you can make the illusion 3D?

If you use only two mirrors, you’ll get a solid background, but add a third mirror and tilt together into a triangle (as shown in the video) and you’ll get the entire field filled with the pattern. You can place transparent objects at the end (like marbles floating in water or mineral oil) or just leave it open and point at the night stars.

The first kaleidoscopes were constructed in 1816 by a scientist while studying polarization. They were quickly picked up as an amusement gadget by the public and have stayed with us ever since.

Materials:

three mirrors the same size
tape and scissors

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Download Student Worksheet & Exercises

Here’s what you do: Carefully tape together three identical mirrors, making a triangle-tube with the mirrors on the inside. (You can also use Mylar or silver wrapping paper taped to cardboard instead of mirrors.) Tape all rough edges well and peek through the opening as you walk around.

Variations: By changing the size and shape of the mirrors, you can change the dimensional effect you see. Just be sure to look at the mirror surface, not the opening. You can also make mirrors wider at the bottom and narrower at the top (easier with cardboard mirrors); use four or five mirrors instead of three; change the length of the mirrors; use curved mirrors instead of flat (find curved cardboard from an oatmeal box or carefully cut apart a soda can and tape Mylar or spray with chrome paint from the hardware store).

Exercises

What is a light source?
What is a light reflector?
Sketch an image of something interesting that you were able to see as the light reflected from the multiple surfaces of the kaleidoscope to your eyes:

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Mixing Colors

Wednesday February 3, 2010

There are three primary colors of light are red, green, and blue. The three primary colors of paint are red, yellow, and blue (I know it’s actually cyan, yellow, and magenta, which we’ll get to in more detail later, but for now just stick with me and think of the primary colors of paint as red-yellow-blue and I promise it will all make sense in the end).

Most kids understand how yellow paint and blue paint make green paint, but are totally stumped when red light and green light mix to make yellow light. The difference is that we’re mixing light, not paint.

Lots of science textbooks still have this experiment listed under how to mix light: “Stir together one of red water and one glass of green water (dyed with food coloring) to get a glass of yellow water.” Hmmm… the result I get is a yucky greenish-brown color. What happened?

The reason you can’t mix green and red water to get yellow is that you’re essentially still mixing paint, not light. But don’t take our word for it – test it out for yourself with this super-fast light experiment on mixing colors.

Materials:

pair of scissors
crayons
sharp wood pencil or wood skewer
index cards
drill (optional)

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Download Student Worksheet & Exercises

Here’s what you do: use a cup to outline circles on a sheet of stiff white paper (or manila folders). Stack several blank pages together and cut out multiple circles. Color the circles, push a sharp wooden pencil through a hole in the center, and spin! What color does yellow and blue make? Pink and purple? You can also make a button-spinner to really whirl it around by looping a length of string through two holes in the center of the disk circle.

Troubleshooting: These disks needs to spin rapidly in order to trick your eye into blending the colors. If you have a motor, batteries, and wires lying around, you can use them to spin the disks for you. Simply punch the motor’s shaft through the paper (colored-side up).

Turn the motor on by connecting the power and watch the colors mix! Other alternatives include using a drill, hand-held mixer/beaters (not a Kitchen Aid standard mixer!), electric screwdriver, etc.

Alternate Spinning Method: Want to do this project, but you don’t have enough speed or a motor? You can make a ‘button spinner’ to whirl these things around super-fast. (Did you know this is how the first circular saws were made?)

Attach your disk to a piece of stiff cardboard (index cards are too flimsy), punch out two holes near the center and thread a loop of string through and tie the ends together to make the old-fashioned “spinning disk”. Using a circling motion with your hands, you can twist up the string with the card in the middle and then pull horizontally outwards to untwist it and watch the cardboard whirl and whip around!!

Click here for the Mixing Cold Light experiment!

Exercises

What happens when blue and red are mixed on the spinner?
What happens when red and green are mixed on the spinner?
What colors would you mix to get orange?
What are the primary colors of light, and how do they differ from the primary colors we learn in art class?

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Diffraction

Wednesday February 3, 2010

Ever play with a prism? When sunlight strikes the prism, it gets split into a rainbow of colors. Prisms un-mix the light into its different wavelengths (which you see as different colors). Diffraction gratings are tiny prisms stacked together.

When light passes through a diffraction grating, it splits (diffracts) the light into several beams traveling at different directions. If you’ve ever seen the ‘iridescence’ of a soap bubble, an insect shell, or on a pearl, you’ve seen nature’s diffraction gratings.

Scientist use these things to split incoming light so they can figure out what fuels a distant star is burning. When hydrogen burns, it gives off light, but not in all the colors of the rainbow, only very specific colors in red and blue. It’s like hydrogen’s own personal fingerprint, or light signature.

Astronomers can split incoming light from a star using a spectrometer (you can build your own here) to figure out what the star is burning by matching up the different light signatures.

Materials:

feather
old CD or DVD

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Here’s what you do: Take a feather and put it over an eye. Stare at a light bulb or a lit candle. You should see two or three flames and a rainbow X. Shine a flashlight on a CD and watch for rainbows. (Hint – the tiny “hairs” on the feather are acting like tiny prisms… take your homemade microscope to look at more of the feather in greater detail and see the tiny prisms for yourself!

What happens when you aim a laser through a diffraction grating? Here’s what you do:

Materials:

laser pointer
diffraction grating (you can use an old CD also)

Download Student Worksheet & Excercises

Exercises

Which light source gave the most interesting results?
What happens when you aim a laser beam through the diffraction grating?
How is a CD different and the same as a diffraction grating?
Why does the feather work?

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Laser Maze

Wednesday February 3, 2010

By using lenses and mirrors, you can bounce, shift, reflect, shatter, and split a laser beam. Since the laser beam is so narrow and focused, you’ll be able to see several reflections before it fades away from scatter. Make sure you complete the Laser Basics experiment first before working with this experiment.

You’ll need to make your beam visible for this experiment to really work. There are several different ways you can do this:

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1. Take your laser with you into a steamy bathroom (which has mirrors!) after a hot shower. The tiny droplets of water in the steam will illuminate your beam. (Psst! Don’t get the laser wet!)

2. If you have carpet, shine your laser under the bed while stomping the floor with your hand. The small particles (dust bunnies?) float up so you can see the beam. Some parents aren’t going to like this idea, sooo….

3. Drop a chunk of dry ice (use gloves!) into a bowl of water and use the fog to illuminate the beam. The drawback to this is that you need to keep adding more dry ice as it sublimates (goes from solid to gas) and replacing the water (when it gets too cold to produce fog).

Materials:

large paper clips
brass fastener
index card
small mirrors (mosaic-type work well)

Download Student Worksheet & Exercises

Here’s what you do: Open up each paper clip into the “L” shape. Insert a brass fastener into one U-shape leg and punch it through the card. Hot glue (or tape) one square mirror to the other end of the L-bracket. Your mirror should be upright and able to rotate. Do this with each mirror. (You can alternatively mount each mirror to a one-inch wooden cube as shown in the video.)

Turn on the laser adjust the mirrors to aim the beam onto the next mirror, and the next! Turn down the lights first and use any one of the methods mentioned above to make your laser beam visible.

What’s happening? The mirrors are bouncing the laser beam to each other, and the effect shows up when you dim the lights and add fog or dust particles to help illuminate the beam. A laser beam is a highly focused beam of light, and you can direct that light and bounce it off mirrors!

Why can’t I see the beam normally? The reason you can’t see the laser beam without the help of a steamy room, dirty carpet, or fog machine is that your eyes are tuned for green light, not red (which is why you can see the beam from a green laser at night).

Exercises

The word LASER is actually an acronym. What does it stand for?
What type of laser did we use in our experiment?
Why can’t we see the laser beams without the help of steam, dirty carpet, etc.?

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Electric Eye

Wednesday February 3, 2010

This is a super-cool and ultra-simple circuit experiment that shows you how a CdS (cadmium sulfide cell) works. A CdS cell is a special kind of resistor called a photoresistor, which is sensitive to light.

A resistor limits the amount of current (electricity) that flows through it, and since this one is light-sensitive, it will allow different amounts of current through depends on how much light it "sees".

Photoresistors are very inexpensive light detectors, and you'll find them in cameras, street lights, clock radios, robotics, and more. We're going to play with one and find out how to detect light using a simple series circuit.

Materials:

AA battery case with batteries
one CdS cell
three alligator wires
LED (any color and type)

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Download Student Worksheet & Exercises

Turn this into a super-cool burglar alarm!

Exercises

How is a CdS cell like a switch? How is it not like a switch?
When is the LED the brightest?
How could you use this as a burglar alarm?

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Materials:

AA battery case with batteries
one CdS cell
three alligator wires
LED (any color and type)

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Download Student Worksheet & Exercises

Turn this into a super-cool burglar alarm!

Exercises

How is a CdS cell like a switch? How is it not like a switch?
When is the LED the brightest?
How could you use this as a burglar alarm?

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Black Light Treasure Hunt

Wednesday February 3, 2010

Ever notice how BRIGHT your white t-shirt looks in direct sun? That’s because mom washed with fluorescent laundry soap (no kidding!). The soap manufacturers put in dyes that glow white under a UV light, which make your clothes appear whiter than they really are.

Since light is a form of energy, in order for things to glow in the dark, you have to add energy first. So where does the energy come from? There are are few different ways to do this:

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Materials:

UV black fluorescent light (check shopping list to find out where to get one)
dark evening inside your house

Light bulbs use incandescence, meaning that the tungsten wire inside a light bulb gets so hot that it gives of light. Unfortunately, bulbs also give off a lot of heat, too. Incandescence happens when your electric stove glows cherry red-hot. Our sun gives off energy through incandescence also – a lot of it.

On the other end of things, cold light refers to the light from a glow stick, called luminescence. A chemical reaction (chemiluminescence) starts between two liquids, and the energy is released in the form of light. On the atomic scale, the energy from the reaction bumps the electron to a higher shell, and when it relaxes back down it emits a photon of light.

Phosphorescence light is the ‘glow-in-the-dark’ kind you have to ‘charge up’ with a light source. This delayed afterglow happens because the electron gets stuck in a higher energy state. Lots of toys and stick-on stars are coated with phosphorescent paints.

Triboluminescence is the spark you see when you smack two quartz crystals together in the dark. Other minerals spark when struck together, but you don’t have to be a rock hound to see this one in action – just take a Wint-O-Green lifesaver in a dark closet with a mirror and you’ll get your own spark show. The spark is basically light from friction.

Fluorescence is what you see on those dark amusement-park rides that have UV lights all around to make objects glow. The object (like a rock) will absorb the UV light and remit a completely different color. The light strikes the electron and bumps it up a level, and when the electron relaxed back down, emits a photon.

Download Student Worksheet & Exercises

Whew! There’s a lot to know about glow in the dark stuff, isn’t there? Let’s pull all this together and go on a Treasure Hunt. This hunt is best done just before bed, when it’s already dark outside. All you need is 20 minutes and a UV black light. Ready?

Here’s what you do: Shut off all the lights in the house and go around armed with your UV light, finding things that glow both inside and outside the house. I’ve found some surprises, including a batch of screaming yellow masking tape, eye-popping orange near the microwave (someone’s spillover from lunch?), and garishly green rocks just outside. Our teeth, laundry soap, and sneakers were way fun, too! What fluoresces in your house? Have fun!

What kind of stuff glows under a black light?

Loads of stuff! There are a bunch of everyday things that fluoresce (glow) when under a black light. Note – black lights emit UV light, some of which you can’t see (just like you can’t see infrared – the beam emitted from the remote control to the TV). By the way, that’s why “black lights” were named as such. The reason stuff glows is that fluorescent objects absorb the UV light and then spit it back almost instantaneously. Some of that energy gets lost during that process, and that changes the wavelength of the light, which makes this light visible and causes the material to appear to ‘glow’.

Here are some things that glow: white paper (although paper made pre-1950 doesn’t, which is how investigators tell the difference between originals and fakes), club soda or tonic water (it’s the quinine that glows blue), body fluids (yes, blood, urine, and more are all fluorescent), Vitamins (Vitamin A, B, B-12 (crush and dissolve in vinegar first), thiamine, niacin, and riboflavin are strongly fluorescent), chlorophyll (grind spinach in a small amount of alcohol (vodka) and pour it through a coffee filter to get the extract (keep the solids in the filter, not the liquid)), antifreeze, laundry detergents, tooth whiteners, postage stamps, driver’s license, jellyfish, and certain rocks (fluorite, calcite, gypsum, ruby, talc, opal, agate, quartz, amber) and the Hope Diamond (which is blue in regular light, but glows red).

When you purchase your UV fluorescent “black lights”, be sure to get the LONG WAVE version (short wave UV is the kind that causes permanent damage to living things – that’s how they kill the bacteria in water), and it appears that UV fluorescent lamps work better than the UV LEDs currently on the market, usually sold as “UV Flashlights”. We tried both, and the stuff shone brighter with the fluorescent lamps.

Exercises

Why are incandescent lights less energy-efficient than fluorescent lights?
What are the two types of fluorescent lights?
What kinds of things did you find that glow on your treasure hunt? Give at least five examples.

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Laser Burglar Alarm

Wednesday February 3, 2010

This is a beefier-version of the Electric Eye that will be able to turn on a buzzer instead of a LED by increasing the voltage in the circuit. This type of circuit is a light-actuated circuit. When a beam of light hits the sensor (the "eye"), a buzzer sounds. Use this to indicate when a door closes or drawer closes... your suspect will never know what got triggered.
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Materials:

Red laser (cheap dollar store kind works well)
9V Battery
Three alligator clip leads
Buzzer (3-6V)
CdS Cell

Download Student Worksheet & Exercises

Exercises

How is this circuit different from the Electric Eye experiment we did previously?
Name three other light sources that work to activate your circuit.

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Laser Light Show

Wednesday February 3, 2010

What happens when you shine a laser beam onto a spinning mirror? In the Laser Maze experiment, the mirrors stayed put. What happens if you took one of those mirrors and moved it really fast?

It turns out that a slightly off-set spinning mirror will make the laser dot on the wall spin in a circle. Or ellipse. Or oval. And the more mirrors you add, the more spiro-graph-looking your projected laser dot gets.

Why does it work? This experiment works because of imperfections: the mirrors are mounted off-center, the motors wobble, the shafts do not spin true, and a hundred other reasons why our mechanics and optics are not dead-on straight. And that’s exactly what we want – the wobbling mirrors and shaky motors make the pretty pictures on the wall! If everything were absolutely perfectly aligned, all you would see is a dot.

Here’s how to do this experiment:

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Materials:

AA battery pack with AA batteries
two 1.5-3V DC motors OR rip them off old toys or personal fans sold in the summertime
keychain laser pointer
clothespin
two round mirrors (mosaic mirrors from the craft store work great)
two alligator clip leads
gear that fits onto the motor and has a flat side to attach to the mirror
5-minute epoxy (don’t use hot glue – it’s not strong enough to hold the mirrors on at high motor speeds)

**Note – if this is your very first time wiring up an electrical circuit, I highly recommend doing this Easy Laser Light Show first. It uses a lot of the same parts, but it’s easier to build.**

Here’s what you do:

1. Insert the batteries into their case.

2. Use 5-minute epoxy to secure the gear onto the round mirror.

3. Press-fit the gear-mirror onto the shaft when the epoxy is dry.

4. Make the motor spin using the alligator clips and the battery case.

5. Turn down the lights and fire up the laser, aiming the beam onto the motor.

6. Shine the reflection somewhere easy to see, like the ceiling.

7. Once you’ve got this working, add a second mirror like you did in the laser maze.

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Advanced Two-Axis Laser Light Show

The second part of this experiment is for advanced students. What shapes can you make? Is it tough to hold it all in place? Then here’s how to create a portable laser light show:

Materials:

Red laser pointer
3VDC motors
2 gears or corks (you’ll need a solid way to attach the mirror to the motor shaft tip)
two 1” round mirrors (use mosaic mirrors)
2 DPDT switches with center off
20 alligator clip leads OR insulated wire if you already know how to solder
2 AA battery packs with 4 AA’s
Two 1K potentiometers
Zip-tie (from the hardware store)
½ ” or ¾ ” metal conduit hangers (size to fit your motors from the hardware store)
3 sets of ¼ ” x 2″ bolts, nuts, and washers
1 project container (at least 7” x 5”) with lid
Basic tools (scissors, hot glue gun, drill, wire strippers, pliers, screwdriver)

Click here to download the Schematic Wiring Diagram for the Advanced Laser Light Show.

Download Student Worksheet & Exercises

Exercises

How does the mirror turn a laser dot into an image?
What happens when you add a second motor? Third?

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Advanced Telescope Building

Wednesday February 3, 2010

So you’ve played with lenses, mirrors, and built an optical bench. Want to make a real telescope? In this experiment, you’ll build a Newtonian and a refractor telescope using your optical bench.

Materials:

optical bench
index card or white wall
two double-convex lenses
concave mirror
popsicle stick
mirror
paper clip
flash light
black garbage bag
scissors or razor
rubber band
wax paper
hot glue

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Download Student Worksheet & Exercises

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Crystal Radio

Wednesday February 3, 2010

In addition to laser experiments, I thought you’d like to learn how to pick up sound that’s traveling on a light wave. A crystal radio is among the simplest of radio receivers – there’s no battery or power source, and nearly no moving parts. The source of power comes directly from the radio waves (which is a low-power, low frequency light wave) themselves.

The crystal radio turns the radio signal directly into a signal that the human ear can detect. Your crystal radio detects in the AM band that have been traveling from stations (transmitters) thousands of miles away. You’ve got all the basics for picking up AM radio stations using simple equipment from an electronics store. I’ll show you how…

The radio is made up of a tuning coil (magnet wire wrapped around a toilet paper tube), a detector (germanium diode) and crystal earphones, and an antenna wire.

One of the biggest challenges with detecting low-power radio waves is that there is no amplifier on the radio to boost the signal strength. You’ll soon figure out that you need to find the quietest spot in your house away from any transmitters (and loud noises) that might interfere with the reception when you build one of these.

One of things you’ll have is to figure out the best antenna length to produce the clearest, strongest radio signal in your crystal radio. I’m going to walk you through making three different crystal radio designs.

You’ll need to find these items below.

Toilet paper tube
Magnet wire
Germanium diode: 1N34A
4.7k-ohm resistor
Alligator clip test leads
100’ stranded insulated wire (for the antenna: option 1 or option 2)
Scrap of cardboard
Brass fasteners (3-4)
Telephone handset or get a crystal earphone

Here’s what you do:

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Fun with UV

Tuesday February 2, 2010

UV (ultra-violet) light is invisible, which means you need more than your naked eyeball to do experiments with it. Our sun gives off light in the UV. Too much exposure to the sun and you’ll get a sunburn from the UV rays.

There are many different experiments you can do with UV detecting materials, such as color-changing UV beads and UV nail polish.

Here are a few fun activities you can do with your UV detecting materials:

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Materials:

UV beads
sunblock
sunglasses
sunlight
clear plastic bag

Testing Sunblock You can test how effective your sunblock is at stopping harmful rays by slapping a coat of the lotion (or SPF-rated lip balm) on the beads and leaving them out in the sun for a minute. Bring the bead indoors and wipe off… did it change color? If so, then UV rays made it through the sunblock to your bead, and chances are that your sunblock isn’t doing it’s job. Does it matter how thick of a coat you layer on?

You can alternatively place the beads inside a plastic bag and coat the outside of the bag with sunblock. And is the sunblock really waterproof? Meaning that they still are white after dunking the beads underwater while sunblocked…?!

Different Times of Day Stick the UV beads outside and take note how bright the colors are in the morning, noon, and afternoon. You’ll notice a big difference depending on the sun’s spot in the sky. Does it matter whether it’s sunny or cloudy?

Absorption and Filtration Test out different lenses and filters to see which block UV light. Lay a handful of beads on the sidewalk and set a pair of sunglasses in top (lenses sitting on the layer of beads). Did any UV light make it through? If it didn’t, your beads should stay white. What other things can you test? (Hint: how about inside your car?)

Download Student Worksheet & Exercises

Why does that work? UV sensitive materials have a pigment inside that changes color when exposed to UV light from either the sun or lights that emit in the 350nm – 300nm wavelength. (UVA is high-energy: 400-320nm, and UVB is low energy: 320-280nm). If you have fluorescent black lights, use them. (Do regular incandescent bulbs work? If not, you know they emit light outside the range of the beads!)

When light hits the pigment molecule, it absorbs the energy and actually expands asymmetrically (one end of the molecule expands more than the other). Different expansion amounts will give you a different color. Although it’s a bit more complicated that that, you now have the basic idea. Your beads will change colors thousands of times before they wear out, so enjoy these super-inexpensive UV detectors!

Exercises

What kinds of light sources didn’t work with the UV beads?
Did your sun block really block out the UV rays?
Which was the best protection against UV rays?

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Squished Soda Can

Sunday January 31, 2010

An average can of soda at room temperature measures 55 psi before you ever crack it open. (In comparison, most car tires run on 35 psi, so that gives you an idea how much pressure there is inside the can!)

If you heat a can of soda, you’ll run the pressure over 80 psi before the can ruptures, soaking the interior of your house with its sugary contents. Still, you will have learned something worthwhile: adding energy (heat) to a system (can of soda) causes a pressure increase. It also causes a volume increase (kaboom!).
How about trying a safer variation of this experiment using water, an open can, and implosion instead of explosion?

Materials – An empty soda can, water, a pan, a bowl, tongs, and a grown-up assistant.

NOTE: If you can get a hold of one, use a beer can – they tend to work better for this experiment. But you can also do this with a regular old soda can. And no, I am not suggesting that kids should be drinking alcohol! Go ask a parent to find you one – and check the recycling bin.

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Prepare an ice bath by putting about ½” of ice water in a shallow dish. With an adult, place a few tablespoons of water in an empty soda or beer can and place the can upright in a skillet on the stove. When the can emits a think trickle of steam, grab the can with tongs and quickly invert it into the ice dish. CRACK!

Troubleshooting: The trick to making this work is that the can needs to be full of hot steam, which is why you only want to use a tablespoon or two of water in the bottom of the can. It’s alright if a bit of water is still at the bottom of the can when you flip it into the ice bath. In fact, there should be some water remaining or you’ll superheat the steam and eventually melt the can. You want enough water in the ice bath to completely submerge the top of the can.

Always use tongs when handling the heated can and make sure you completely submerge the top of the can in the icy water. The water needs to seal the hole in the top of the can so the steam doesn’t escape. Be prepared for a good, loud CRACK! when you get it right.

Why does this work? By heating up the water in the can, you’re changing the state of water from a liquid to a has (called water vapor), which drives out the air, leaving the steam inside. When inverted and cooled, the steam condenses to a small volume of liquid water (much smaller than if it was just hot air). The molecules in water vapor are a lot further apart than when they are in a liquid state. Since the air inside the can has been replaced by the steam, when it cools quickly, it creates a lower air pressure region in the can, so the air pressure surrounding the outside of the can rapidly crushes the can.

If you look really carefully as it condenses, you’ll see cold water from the bowl zoom into the can, just like when you suck water through a straw. The vacuum created int he can by the condensing steam creates a lower pressure, which pushes water into the can itself. When you suck from a straw, you’re creating a lower air pressure region in your mouth so that the surrounding air pressure pushes liquid up the straw to equalize the pressure.

Remember, high pressure always pushes!

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Hidden Carbon Dioxide

Sunday January 10, 2010

If you’ve ever burped, you know that it’s a lot easier to do after chugging an entire soda. Now why is that?

Soda is loaded with gas bubbles — carbon dioxide (CO₂), to be specific. And at standard temperature (68^oF) and pressure (14.7 psi), carbon dioxide is a gas. However, if you burped in Antarctica in the wintertime, it would begin to freeze as soon as it left your lips. The freezing temperature of CO2 is -109^oF, and Antarctic winters can get down to -140^oF. You’ve actually seen this before, as dry ice (frozen burps!).

Carbon dioxide has no liquid state at low pressures (75 psi or lower), so it goes directly from a block of dry ice to a smoky gas (called sublimation). It’s also acidic and will turn cabbage juice indicator from blue to pink. CO₂ is colorless and odorless, just like water, but it can make your mouth taste sour and cause your nose to feel as if it’s swarming with wasps if you breathe in too much of it (though we won’t get anywhere near that concentration with our experiments).

The triple point of CO₂ (the point at which CO₂ would be a solid, a liquid, and a gas all at the same time) is around five times the pressure of the atmosphere (75 psi) and around -70^oF. (What would happen if you burped then?)

What sound does a fresh bottle of soda make when you first crack it open? PSSST! What is that sound? It’s the CO₂ (carbon dioxide) bubbles escaping. What is the gas you exhale with every breath? Carbon dioxide. Hmmm … it seems as if your soda is already pre-burped. Interesting.

We’ll actually be doing a few different experiments, but they all center around producing burps (carbon dioxide gas). The first experiment is more detective work in finding out where the CO₂ is hiding. With the materials we’ve listed (chalk, tile, limestone, marble, washing soda, baking soda, vinegar, lemon juice, etc. …) and a muffin tin, you can mix these together and find the bubbles that form, which are CO₂. (Not all will produce a reaction.) You can also try flour, baking powder, powdered sugar, and cornstarch in place of the baking soda. Try these substitutes for the vinegar: water, lemon juice, orange juice, and oil.

Materials:

baking soda
chalk
distilled white vinegar
washing soda
disposable cups and popsicle sticks

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Download Student Worksheet & Exercises

The next video (below) is a BONUS video for you – can you find the items around your house so you can make your own scale? (If you generate a lot of CO₂, you can simply use paper grocery bags suspended on both ends of a broom handle (disconnect the broom part first). Suspend the center of the broom handle from a length of string for pin-point accuracy.

The second part of this experiment (video below) compares the weight of air with the weight of carbon dioxide. Make sure your balance is free to move easily when the lightest touch (your breath) is applied to one of the scales. You can use grocery bags attached to the ends of a broom handle for a larger scale, or modify tiny cups with string and pencils (as shown in the video). Either one works, but you’ll want to be sure the bubbles are (mostly) popped before you pour. And pour carefully or you’ll slosh out the invisible CO₂ gas.

You can create the CO₂ gas in a variety of ways (the image at right shows dry ice submerged in water), including the standard vinegar and baking powder method. Here is another option: Open a 2-liter bottle of soda and quickly pour it into a big pitcher so that it foams up to the top of the container. Carefully pour the gas from the pitcher into the balance. What happens?

Fire extinguisher variation: You can create a fire extinguisher by “pouring” the CO₂ gas onto a lit candle to snuff it out.

Materials:

baking soda
distilled white vinegar
two disposable cups
large container
two water bottles or stacks of books
two long pencils or skewers
string

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Turning Water into Wine

Sunday January 10, 2010

Phenolphthalein is a weak, colorless acid that changes color when it touches acidic (turns orange) or basic (turns pink/fuchsia) substances. People used to take it as a laxative (not recommended today, as ingesting high amounts may cause cancer). Use gloves when handling this chemical, as your skin can absorb it on contact. I’ll show you how:

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Materials:

2 test tubes
sodium carbonate (washing soda)
phenolphthalien (liquid)
medicine dropper
water
test tube stoppers
gloves and goggles

Download Student Worksheet & Exercises

Sprinkle a tiny amount of sodium carbonate into the bottom of your test tube. Fill your test tube partway with water (the solution should still be clear). Add a few drops of phenolphthalein (which is clear inside the dropper), cap, and shake.

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Turning Water into Ink

Sunday January 10, 2010

You can use this as real ink by using it BEFORE you combine them together like this: dip a toothpick into the first solution (sodium ferrocyanide solution) and with the tip write onto a sheet of paper.

While the writing is drying, dip a piece of paper towel int other solution (ferric ammonium sulfate solution) and gently blot along where you wrote on the paper… and the color appears as blue ink. You can make your secret message disappear by wiping a paper towel dipped in a sodium carbonate solution.

You can also grow purple, gold, and red crystals with these chemicals… we’ll show you how!

Materials:

sodium ferrocyanide
ferric ammonium sulfate
2 test tubes
distilled water
goggles and gloves
water

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Download Student Worksheet & Exercises

CAUTION: Do not mix sodium ferrocyanide with any other chemical other than specified here, as it can produce hydrogen cyanide gas, which is lethal. Handle this chemical with care, wear gloves, and keep it locked away when not in use.

Measure out a tiny bit of sodium ferrocyanide into a test tube filled partway with water. You want to add enough of the crystals so that when you shake the solution (with the cap on), all of the crystals dissolve into the water and make a saturated solution.

Into a second test tube, dissolve another tiny bit of ferric ammonium sulfate in water, adding just enough to make a saturated solution. When you’re ready, pour one test tube into the other and note the change!

Bonus Experiment Idea! You can grow yellow-gold crystals by cooling off a cup of hot water. Here’s how: into a test tube, add 40 drops of hot water and 1 small spoon measure of sodium ferrocyanide. Suspend a small pebble attached to a thread into the test tube (this is your starter-seed for your crystals to attach to). If after a day or two your crystals aren’t growing, just reheat the solution and add a little bit more of the chemical. To grow purple crystals, use ferric ammonium sulfate instead of the sodium ferro-cyanide. You can also use 2 spoonfuls of cobalt chloride in a fresh test tube to grow red-colored crystals.

ANOTHER Bonus Experiment Idea!Mix 1/3 measure of ferric ammonium sulfate and 1/3 measure of sodium Ferro-cyanide in a glass 1/2 full of water. To another glass 1/2 full of water, add 5 drops of phenolphthalein solution. In an empty glass put 1 spoonful of sodium silicate powder and 2 spoonfuls of water. Pour the contents of these last two glasses into the first glass, stir and watch what happens.
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Hot Liquids and Cool Solids

Sunday January 10, 2010

Dissolving calcium chloride is highly exothermic, meaning that it gives off a lot of heat when mixed with water (the water can reach up to 140^oF, so watch your hands!). The energy released comes from the bond energy of the calcium chloride atoms, and is actually electromagnetic energy.

When you combine the calcium chloride and sodium carbonate solutions, you form the new chemicals sodium chloride (table salt) and calcium carbonate. Both of these new chemicals are solids and “fall out” of the solution, or precipitate. If you find that there is still liquid in the final solution, you didn’t have quite a saturation solution of one (or both) initial solutions.

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Materials:

calcium chloride (AKA: “ice melt” or “Dri-EZ”)
sodium carbonate (AKA: “washing soda”)
two disposable cups
two test tubes with caps
medicine dropper
distilled water
goggles and gloves

Download Student Worksheet & Exercises

Mix up a saturated solution of calcium chloride in one test tube and a saturated solution of sodium carbonate in the other. Here’s how to do this:

Sprinkle 1 teaspoon of calcium chloride into a disposable cup. Add in a few tablespoons of water and stir, dissolving as much of the solid into the water as possible. Add more calcium chloride until you see bits of it at the bottom that refuse to dissolve. Now pour only the liquid into your test tube; the liquid is your saturated solution. Do the same for the sodium carbonate.

Do the test tubes feel hot or cold? Pour one test tube into another.

Instant solid.

Calcium chloride is hygroscopic (absorbs moisture), exothermic (releases heat when melted or dissolved), and deliquescent (dissolves in the moisture it absorbs and retains it for a long time).

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Elephant Toothpaste

Sunday January 10, 2010

I mixed up two different liquids (potassium iodide and a very strong solution of hydrogen peroxide) to get a foamy result at a live workshop I did recently. See what you think!

Note: because of the toxic nature of this experiment, it’s best to leave this one to the experts.

Nurses will put hydrogen peroxide on a cut to kill germs. It’s also used in rocket fuel as an oxidizer. The hydrogen peroxide in your grocery store is a weak 3% solution. The hydrogen peroxide used here is 10X stronger than the grocery store variety. The KI (potassium iodide) is the catalyst in the experiment which speeds up the decomposition of the hydrogen peroxide. This is an exothermic reaction (gives off heat).

What is Fire?

Sunday January 10, 2010

What state of matter is fire? Is it a liquid? I get that question a LOT, so let me clarify. The ancient scientists (Greek, Chinese… you name it) thought fire was a fundamental element. Earth, Air Water, and Fire (sometimes Space was added, and the Chinese actually omitted Air and substituted Wood and Metal instead) were thought to be the basic building blocks of everything, and named it an element. And it’s not a bad start, especially if you don’t have a microscope or access to the internet.

Today’s definition of an element comes from peeking inside the nucleus of an atom and counting up the protons. In a flame, there are lots of different molecules from NO, NO₂, NO₃, CO, CO₂, O₂, C… to name a few. So fire can’t be an element, because it’s made up of other elements. So, what is it?

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Fire is a combination of different gases and hot plasma. It’s a complicated exothermic (gives off heat) chemical reaction that releases a lot of heat and light (you can feel and see the flame). You need three things for a flame: oxygen, fuel, and a spark. When you take away one of these three, you snuff the flame and stop the chemical reaction. You start with fuel (usually contains carbon), and add oxygen to get carbon dioxide, carbon monoxide, nitric oxide, and many other gases and leftover ash. Most flames are hot enough to heat the gas mixture to create tiny bits of plasma within the flame, so fire is actually involved in two states of matter.

In this experiment, we’re going to see how you can protect a surface from burning using water. Are you ready?

Materials:

Shallow baking dish
Tongs
Rubbing Isopropyl Alcohol (50-91%)
Water (omit if using 50-70% alcohol)
Dollar bill
Fire extinguisher
Adult help

Download Student Worksheet & Exercises

What’s going on? Alcohol burns with a slightly blue and orange flame (as shown in the video). The secret to keeping the dollar bill from burning is the water you mixed in with the alcohol. Water has a high heat capacity, which means that the water absorbs the energy from the flame and keep the bill from catching on fire. If you dipped the dollar bill in pure 100% alcohol, the temperature would rise high enough on the bill to burn. The reason we chose a bill instead of regular paper is that the dollar bill is a combination of linen and paper, making it much stronger and absorbent for this experiment.

You need both the water and the alcohol for this experiment. The water, as it absorbs the energy from the flame, heats up to its boiling point and then vaporizes, keeping the bill cool enough to not catch on fire. The alcohol is the fuel needed to keep the flame going. It’s a delicate balance between the two, but here are a couple of variations you can try out:

You can change the color of the flame by adding in a sprinkling of salt (for yellow), boric acid (for green), or epsom salt (for white).

You can also try mixing different ratios of water to alcohol, using 50%, 70% and 91% isopropyl alcohol. You can also try ethyl alcohol (which is an entirely different molecule) but will react about the same with this experiment. Note that if you decrease the water content too much, you’re going to lose your dollar bill.

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Decomposing Hydrogen Peroxide

Sunday January 10, 2010

This experiment below is for advanced students. If you’ve ever wondered why hydrogen peroxide comes in dark bottles, it’s because the liquid reacts with sunlight to decompose from H₂O₂ (hydrogen peroxide) into H₂O (water) and O₂ (oxygen). If you uncap the bottle and wait long enough, you’ll eventually get a container of water (although this takes a LOOONG time to get all of the H₂O₂ transformed.)

Here’s a way to speed up the process and decompose it right before your eyes. For younger kids, you can modify this advanced-level experiment so it doesn’t involve flames. Here’s what you do:

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Materials:

hydrogen peroxide
empty water bottle
balloon
charcoal piece

Want to do this experiment with a more dramatic flair? Try speeding it up as shown in the video below.

IMPORTANT: DO NOT DRINK ANYTHING FROM THIS LAB!!

Pour hydrogen peroxide into an empty plastic water bottle. Add a scoop of activated charcoal (you can also smash regular charcoal with a hammer to get it to fit – the smaller the bits, the better it will work, but make sure you do NOT use charcoal pre-soaked in lighter fluid). Cap your bottle with a helium-quality latex balloon and set aside. After several hours, you will have a balloon filled with oxygen.

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Taking the Salt out of the Ocean

Sunday January 10, 2010

This experiment is for advanced students.Have you ever taken a gulp of the ocean? Seawater can be extremely salty! There are large quantities of salt dissolved into the water as it rolled across the land and into the sea. Drinking ocean water will actually make you thirstier (think of eating a lot of pretzels). So what can you do if you’re deserted on an island with only your chemistry set?

Let me show you how to take the salt out of water with this easy setup.

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Materials:

salt
water
alcohol burner
flask with one-hole stopper
stand with wire mesh screen
two 90-degree glass pipes
flexible tubing
ring stand with clamp
lighter with adult help

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Can Fish Drown?

Sunday January 10, 2010

If you’ve ever owned a fish tank, you know that you need a filter with a pump. Other than cleaning out the fish poop, why else do you need a filter? (Hint: think about a glass of water next to your bed. Does it taste different the next day?)

There are tiny air bubbles trapped inside the water, and you can see this when you boil a pot of water on the stove. The experimental setup shown in the video illustrates how a completely sealed tube of water can be heated… and then bubbles come out one end BEFORE the water reaches a boiling point. The tiny bubbles smoosh together to form a larger bubble, showing you that air is dissolved in the water.

Materials:

test tube clamp
test tube
lighter (with adult help)
alcohol burner or votive candle
right-angle glass tube inserted into a single-hole stopper
regular tap water

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Download Student Worksheet & Exercises

The filter pump in your fish tank ‘aerates’ the water. The simple act of letting water dribble like a waterfall is usually enough to mix air back in. Which is why flowing rivers and streams are popular with fish – all that fresh air getting mixed in must feel good! The constant movement of the river replaces any air lost and the fish stay happy (and breathing). Does it make sense that fish can’t live in stagnant or boiled water?

You don’t need the fancy equipment show in this video to do this experiment… it just looks a lot cooler. You can do this experiment with a pot of water on your stove and watch for the tiny bubbles before the water reaches 212^oF.

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Turning Copper into Silver into Gold

Sunday January 10, 2010

No kidding! You’ll be able to show your friends this super-cool magic show chemistry trick with very little fuss (once you get the hang of it). This experiment is for advanced students. Before we start, here are a few notes about the setup to keep you safe and your nasal passages intact:

The chemicals required for this experiment are toxic! This is not an experiment to do with little kids or pets around, and you want to do the entire experiment outside or next to an open window for good ventilation, as the fumes from the sodium hydroxide/zinc solution should not be inhaled.

This experiment is not dangerous when you follow the steps I’ve outlined carefully. I’ll take you step by step and show you how to handle the chemicals, mix them properly, and dispose of the waste when you’re done.

Goggles and gloves are a MUST for this experiment, as the sodium hydroxide (in both liquid and solid form) is caustic and corrosive and will burn your skin on contact.

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Is it REAL gold?

No. But it’s very close in color, as is the ‘silver’. The basic idea behind the experiment is this: by cleaning the pennies in the first step, you clear off any oxide layers to expose the copper surface. When you dip it in the solution, a galvanization reaction starts (just like ‘galvanized nails’) covering the penny with a metallic silver zinc coating.

The torching process fuses the zinc and the copper together to make the gold colored brass coating. Be careful, though, as brass has a low melting temperature and if you leave it in the flame too long, you’ll burn off the brass coating.

Materials:

propane torch with adult help
shiny copper pennies
distilled white vinegar
Pyrex glass beaker
sodium hydroxide (solid)
zinc powder (dust)
alcohol burner
stand that fits over the alcohol burner
lighter with adult help
wire mesh screen
popsicle sticks
water
salt
disposable cup
gloves
goggles
tweezers or pliers

Download Student Worksheet & Exercises

The chemical reaction plates the copper on the penny with zinc (called galvanization). The zinc reacts with the hot sodium hydroxide solution to form soluble sodium zincate (Na₂ZnO₂), which is converted to metallic zinc when it hits the surface of the penny.

Heating the penny fuses the zinc and copper together to form an alloy called brass. The amounts of copper and zinc in brass can vary a lot, from 60-82% copper and 18-40% zinc.

DISPOSAL INSTRUCTIONS: If you simply wipe out the beaker with a paper towel and toss it in the trash, you run the risk of igniting your trash can because the combination of sodium hydroxide and zinc is very exothermic (lots of heat is generated).

Make sure to use plenty of water to remove the sodium hydroxide first before removing the metal. Sodium hydroxide will not harm the plumbing in the sink as it is also used as a drain cleaner (dissolves hair, etc.) but don’t get it on your hands! Vinegar will neutralize any residual sodium hydroxide.

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Fruit Battery

Sunday January 10, 2010

This experiment shows how a battery works using electrochemistry. The copper electrons are chemically reacting with the lemon juice, which is a weak acid, to form copper ions (cathode, or positive electrode) and bubbles of hydrogen.

These copper ions interact with the zinc electrode (negative electrode, or anode) to form zinc ions. The difference in electrical charge (potential) on these two plates causes a voltage.

Materials:

one zinc and copper strip
two alligator wires
digital multimeter
one fresh large lemon or other fruit

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Download Student Worksheet & Exercises

Roll and squish the lemon around in your hand so you break up the membranes inside, without breaking the skin or leaking any juice. If you’re using non-membrane foods, such as an apple or potato, you are all ready to go.

Insert the copper and zinc strips into the lemon, making sure they do not contact each other inside. Clip one test wire to each metal strip using alligator wires to connect to the digital multimeter. Read and record your results.

What happens when you gently squeeze the lemon? Does the voltage vary over time?

You can try potatoes, apples, or any other fruit or vegetable containing acid or other electrolytes. You can use a galvanized nail and a copper penny (preferably minted before 1982) for additional electrodes.

If you want to light a light bulb, try using a low-voltage LED in the 1.7V or lower hooked up to several lemons connected in series. For comparison, you’ll need about 557 lemons to light a standard flashlight bulb.

What’s going on?

The basic idea of electrochemistry is that charged atoms (ions) can be electrically directed from one place to the other. If we have a glass of water and dump in a handful of salt, the NaCl (salt) molecule dissociates into the ions Na+ and Cl-.

When we plunk in one positive electrode and one negative electrode and crank up the power, we find that opposites attract: Na+ zooms over to the negative electrode and Cl- zips over to the positive. The ions are attracted (directed) to the opposite electrode and there is current in the solution.

Electrochemistry studies chemical reactions that generate a voltage and vice versa (when a voltage drives a chemical reaction), called oxidation and reduction (redox) reactions. When electrons are transferred between molecules, it’s a redox process.

Fruit batteries use electrolytes (solution containing free ions, like salt water or lemon juice) to generate a voltage. Think of electrolytes as a material that dissolves in water to make a solution that conducts electricity. Fruit batteries also need electrodes made of conductive material, like metal. Metals are conductors not because electricity passes through them, but because they contain electrons that can move. Think of the metal wire like a hose full of water. The water can move through the hose. An insulator would be like a hose full of cement – no charge can move through it.

You need two different metals in this experiment that are close, but not touching inside the solution. If the two metals are the same, the chemical reaction doesn’t start and no ions flow and no voltage is generated – nothing happens.

Exercises

What kinds of fruit make the best batteries?
What happens if you put one electrode in one fruit and one electrode in another?
What happens if you stick multiple electrode pairs around a piece of fruit, and connect them in series (zinc to copper to zinc to copper to zinc…etc.) and measure the voltage at the start and end electrodes?

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Cobalt Colors

Sunday January 10, 2010

Cobalt chloride (CoCl₂) has a dramatic color change when combined with water, making it a great water indicator. A concentrated solution of cobalt chloride is red at room temperature, blue when heated, and pale-to-clear when frozen. The cobalt chloride we’re using is actually cobalt chloride hexahydrate, which means that each CoCl₂ molecule also has six water molecules (6H₂O) stuck to it.

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For this experiment you’ll need:

cobalt chloride
cotton swab
goggles
test tube with stopper
index card
distilled water
hair dryer

Download Student Worksheet & Exercises

Fill your test tube partway with water and add 1 teaspoon of cobalt chloride. Cap and shake until the solids dissolve. Continue to add cobalt chloride, 1 teaspoon at a time, until you cannot dissolve any more into your solution. (You have just made a saturated solution.)

Using your cotton swab like a paintbrush, dip into the solution (your “paint”) and write on the index card. Use a hair dryer to blow across the solution. (Be careful not to scorch the paper!) What happens? Stick it in the freezer. Now what happens? What if you blow dry it after it comes out of the freezer? What else can you come up with? What happens if you spritz it with water?

What’s Going On? The cobalt changes color when hydrated/dehydrated – think of it as an indicator for water. It should be red when you first mix it, but blue when hit with the hair dryer. It doesn’t react to acids and bases the way the anthocyanin (in red cabbage juice) or universal indicator does, but rather with humidity.

Bonus Experiment Idea! You can grow red crystals by cooling off a cup of hot water. Here’s how: into a test tube, add 40 drops of hot water and 2 small spoon measure of cobalt chloride. Suspend a small pebble attached to a thread into the test tube (this is your starter-seed for your crystals to attach to). If after a day or two your crystals aren’t growing, just reheat the solution and add a little bit more of the chemical.

ANOTHER Bonus Experiment Idea! By soaking a strip of tissue or crepe paper (it’s got to be thin) in the cobalt chloride solution, you can create your own weather forecaster! Simply let dry and when it turns blue, you’re in for blue skies and pink means it’s going to rain. (It’s basically a humidity gauge.)

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Electroplating

Sunday January 10, 2010

If you don’t have equipment lying around for this experiment, wait until you complete Unit 10 (Electricity) and then come back to complete this experiment. It’s definitely worth it!

Electroplating was first figured out by Michael Faraday. The copper dissolves and shoots over to the key and gets stuck as a thin layer onto the metal key. During this process, hydrogen bubbles up and is released as a gas. People use this technique to add material to undersized parts, for place a protective layer of material on objects, to add aesthetic qualities to an object.

Materials:

one shiny metal key
2 alligator clips
9V battery clip
copper sulfate (MSDS)
one copper strip or shiny copper penny
one empty pickle jar
9V battery

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Download Student Worksheet & Exercises

Place the copper sulfate in your jar and add a thin stream of water as you stir. Add enough water to make a saturated solution (dissolves most of the solids). Connect one alligator wire to the copper strip and the positive (red) wire from the clip lead. Connect the other alligator wire to the key and the negative (black) lead.

Place the copper strip and the key in the solution without touching each other. (If they touch, you’ll short your circuit and blow up your battery.) Let this sit for a few minutes… and notice what happens.

Clean up: Clean everything thoroughly after you are finished with the lab. After cleaning with soap and water, rinse thoroughly. Chemists use the rule of “three” in cleaning glassware and tools. Rinse three times, wash with soap, rinse three times.

Wipe off the electrodes. The solution and solids at the bottom of your cup cannot go in the trash. The liquid contains copper, a toxic heavy metal that needs proper disposal and safety precautions. Another chemical reaction needs to be performed to remove the heavy metal from the copper sulfate: Add a thumb sized piece of steel wool to the solution. The chemical reaction will pull out the copper out of the solution. The liquid can be washed down the drain. The solids cannot be washed down the drain, but they can be put in the trash. Use a little water to rinse the container free of the solids.

Place all chemicals, cleaned tools, and glassware in their respective storage places.

Dispose of all solid waste in the garbage. Liquids can be washed down the drain with running water. Let the water run awhile to ensure that they have been diluted and sent downstream.

Exercises

Look at your key. What color is it?
Where did the copper on your key come from?
What happened when you added a second battery?
Which circuit (series or parallel) did the reaction accelerate faster with?

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Iodine Rainbow

Sunday January 10, 2010

This is the experiment that your audience will remember from your chemistry magic show. Here’s what happens – you call up six ‘helpers’ and hand each a seemingly empty test tube. Into each test tube, pour a little of the main gold-colored solution, say a few magic words, and their test tubes turn clear, black, pink, gold, yellow, and white. With a flourish, ask them to all pour their solutions back into yours and the final solution turns from inky black to clear. Voila!

I first saw a similar experiment when I was a kid, and I remembered it all the way through college, where I asked my professor how I could duplicate the experiment on my own. I was told that the chemicals used in that particular experiment were way too dangerous, and no substitute experiment was possible, especially for the color reversal at the end. I was determined to figure out an alternative. After two weeks of nothing but chemistry and experiment testing, I finally nailed it – and the best part is, you have most of these chemicals at the grocery store. (And the best part is, I can share it with you as I’ve eliminated the nasty chemicals so you don’t have to worry about losing an eyeball or a finger.)

NOTE: This experiment requires adult help, as it uses chemicals that are toxic if randomly mixed together. Follow the instructions carefully, and do not mix random chemicals together.

Are you ready to mix up your own rainbow?

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Materials:

Iodine (non-clear, non-ammonia from the pharmacy)
Hydrogen peroxide (3% solution)
Vinegar (distilled white is best)
Cornstarch (tiny pinch) or one starch packing peanut
Water (distilled)
Sodium Thiosulfate
Sodium Carbonate (AKA: “washing soda“)
Phenolphthalein (keep this out of reach of kids) – this is optional
Disposable plastic cups (about eight)
Popsicle sticks
Gloves for your hands
Goggles for your face
Medicine droppers (at least four)

Download Student Worksheet & Exercises

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Chemical Matrix of Acids & Bases

Sunday January 10, 2010

If you love the idea of mixing up chemicals and dream of having your own mad science lab one day, this one is for you. You are going to mix up each solid with each liquid in a chemical matrix.

In a university class, one of the first things you learn in chemistry is the difference between physical and chemical changes. An example of a physical change happens when you change the shape of an object, like wadding up a piece of paper. If you light the paper wad on fire, you now have a chemical change. You are rearranging the atoms that used to be the molecules that made up the paper into other molecules, such as carbon monoxide, carbon dioxide, ash, and so forth.

How can you tell if you have a chemical change? If something changes color, gives off light (such as the light sticks used around Halloween), or absorbs heat (gets cold) or produces heat (gets warm), it’s a chemical change.

What about physical changes? Some examples of physical changes include tearing cloth, rolling dough, stretching rubber bands, eating a banana, or blowing bubbles.

About this experiment: Your solutions will turn red, orange, yellow, green, blue, purple, hot, cold, bubbling, foaming, rock hard, oozy, and slimy, and they’ll crystallize and gel — depending on what you put in and how much!

This is the one set of chemicals that you can mix together without worrying about any lethal gases. I do recommend doing this OUTSIDE, as the alcohol and peroxide vapors can irritate you. Always have goggles on and gloves on your hands, and a hose handy in case of spills. Although these chemicals are not harmful to your skin, they can cause your skin to dry out and itch. Wear gloves (latex or similar) and eye protection (safety goggles), and if you’re not sure about an experiment or chemical, just don’t do it. (Skip the peroxide and cold pack if you have small kids.)

Materials:
• sodium tetraborate (borax, a laundry whitener)
• sodium bicarbonate (baking soda)
• sodium carbonate (washing soda)
• calcium chloride (also known as “DriEz” or “Ice Melt”)
• ammonium nitrate (single-use disposable cold pack)
• isopropyl rubbing alcohol
• hydrogen peroxide
• acetic acid (distilled white vinegar)
• water
• liquid dish soap (add to water)
• muffin tin or disposable cups
• popsicle sticks for stirring and mixing
• tablecloths (one for the table, another for the floor)
• head of red cabbage (indicator)

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Download Student Worksheet & Exercises

Step 1: Cover your kitchen table with a plastic tablecloth (and possibly the floor). Place your chemicals on the table. A set of muffin cups make for an excellent chemistry experiment lab. (Alternatively, you can use empty plastic ice cube trays.) You will mix in these cups. Leave enough space in the cups for your chemicals to mix and bubble up — don’t fill them all the way when you do your experiments!

Step 2: Set out your liquid chemicals in easy-to-pour containers, such as water bottles (be sure to label them, as they all will look the same): alcohol, hydrogen peroxide, water, acetic acid, and dish soap (mixed with water). Set out small bowls (or zipper bags if you’re doing this with a crowd) of the powders with the tops of your water bottles as scoopers. The small scoopers regulate the amounts you need for a muffin-sized reaction. Label the powders, as they all look the same.

Step 3: Prepare the indicator by coarsely chopping the head of red cabbage and boiling the pieces for five minutes in a pot full of water. Carefully strain out all the pieces with a fine-mesh strainer; the reserved liquid is your indicator (it should be blue or purple).

When you add this indicator to different substances, you will see a color range: hot pink, tangerine orange, sunshine yellow, emerald green, ocean blue, velvet purple, and everything in between. Test out the indicator by adding drops of cabbage juice to something acidic, such as lemon juice, and see how different the color is when you add indicator to a base, such as baking soda mixed with water.

Have your indicator in a bottle by itself. An old soy sauce bottle with a built-in regulator that keeps the pouring to a drip is perfect. You can also use a bowl with a bulb syringe, but cross-contamination could be a problem. Or it could not be — depending on whether you want the kids to see the effects of cross-contamination during their experiments. (The indicator bowl will continually turn different colors throughout the experiment.)

Step 4: Start mixing it up! When I teach this class, I let them have at all the chemicals at once (even the indicator), and of course, this leads to a chaotic mix of everything. When the chaos settles down, and they start asking good questions, I reveal a second batch of chemicals they can use. (I have two identical sets of chemicals, knowing that the first set will get used up very quickly.)

Step 5: After the initial burst of enthusiasm, your kids will instinctively start asking better questions. They will want to know why their green goo is creeping onto the floor while someone else’s just bubbled up hot pink, seemingly mixed from the same stuff. Give them a chance to figure out a more systematic approach, and ask if they need help before you jump in to assist.

What’s happening with the indicator? An indicator is a compound that changes color when you dip it in different things, such as vinegar, alcohol, milk, or baking soda mixed with water. There are several extracts you can use from different substances. You’ll find that different indicators are affected differently by acids and bases. Some change color only with an acid, or only with a base. Turmeric, for example, is good only for bases. (You can prepare a turmeric indicator by mixing 1 teaspoon turmeric with 1 cup rubbing alcohol.)

Why does red cabbage work? Red cabbage juice has anthocyanin, which makes it an excellent indicator for these experiments. Anthocyanin is what gives leaves, stems, fruits, and flowers their colors. (Did you know that certain flowers, such as hydrangeas, are blue in acidic soil but turn pink when transplanted to a basic soil?) You’ll need to get the anthocyanin out of the cabbage and into a more useful form so you can use it as a liquid indicator.

Tip for Testing Chemical Reactions: Periodically hold your hand under the muffin cups to test the temperature. If it feels hot, it’s an exothermic reaction (giving off energy in the form of heat, light, explosions …). The chemical-bond energy is converted to thermal energy (heat) in these experiments. If it feels cold, you’ve made an endothermic reaction (absorbing energy, where the heat from the mixture converts to bond energy). Sometimes you’ll find that your mixture is so cold that it condenses the water outside the container (like water drops on the outside of an ice-cold glass of water on a hot day).

Variations for the Indicator: Red cabbage isn’t the only game in town. You can make an indicator out of many other substances, too. Here’s how to prepare different indicators:
• Cut the substance into smaller pieces. Boil the chopped substance for five minutes. Strain out the pieces and reserve the juice. Cap the juice (indicator) in a water bottle, and you’re ready to go.
• What different substances can you use? We’ve had the best luck with red cabbage, blueberries, red and green grapes, beets, cherries, and turmeric. You can make indicator paper strips using paper towels or coffee filters. Just soak the paper in the indicator, remove and let dry. When you’re ready to use one, dip it in partway so you can see the color change and compare it to the color it started out with.
• Use the indicator both before and after you mix up chemicals. You will be surprised and dazzled by the results!

Teaching Tips: You can make this lab more advanced by adding a postage scale (to measure the solids in exact measurements), small beakers and pipettes for the liquid measurements, and data sheets to record temperature, reactivity, and acid/base indicator levels. (Hint: Make the data sheet like a matrix, to be sure you get all the possible combinations.)

For the student: Your mission is to mix up solutions that:
• Generate heat (exothermic)
• Get ice-cold on their own (endothermic)
• Crystallize
• Are self-gelling
• Bubble up and spit
• Ooze creepy concoctions
• Are the most impressive (the ooohhhh-aaahhhhh factor).

For the parent: Your mission is to:
• Make sure everything in reach is covered with plastic tablecloths, drop cloths, or tarps
• Open all the windows and turn on the fans (or just do this experiment outside near the hose)
• Keep all small children and pets away
• Slap on a pair of rubber gloves
• Encourage the kids to try it and test it
• Remember that there are no such things as mistakes, only learning opportunities. (Don’t forget that we usually learn more from mistakes than we do when we’re successful!)

For the truly exceptional parent: Your mission is also to:
• Secretly get an identical second set of chemicals from the grocery store (see shopping list above) and hide them in a bin nearby
• Have all the chemicals out and ready for the kids to use
• Be sure the kids know your rules before you let them loose (no eating, running, or horseplay; all goggles must stay on; etc.)
• Have a bin full of water nearby for washing up
• Let the kids loose to experiment and play without expectation
• Play with the kids, get into the act (“Wow! It turned green! How did you do that?!” instead of “Well, I’m not going to clean THAT up.”)
• Expect kids to dump everything and mix it all together at the same time without much thought about what they are trying to accomplish
• When their supplies run out, pull out your second bin and smile
• Encourage the kids to try their ideas out
o When they ask, “Will this work?” you can reply
with confidence, “I don’t know — try it!”

Click here to view another version of this experiment: Acids & Bases.
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Iodine Clock Reaction

Sunday January 10, 2010

First discovered in 1886 by Hans Heinrich Landolt, the iodine clock reaction is one of the best classical chemical kinetics experiments. Here’s what to expect: Two clear solutions are mixed. At first there is no visible reaction, but after a short time, the liquid suddenly turns dark blue.

Usually, this reaction uses a solution of hydrogen peroxide with sulfuric acid, but you can substitute a weaker (and safer) acid that works just as well: acetic acid (distilled white vinegar). The second solution contains potassium iodide, sodium thiosulfate (crystals), and starch (we’re using a starch packing peanut, but you can also use plain old cornstarch). Combine one with the other to get the overall reaction, but note that there are actually two reactions happening simultaneously.

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Materials:

sodium thiosulfate
potassium iodide
two plastic test tubes
packing peanut
disposable droppers
hydrogen peroxide
distilled white vinegar
distilled water
four disposable cups
popsicle sticks
clock
measuring spoons and cups
goggles and gloves

Download Student Worksheet & Exercises

In the first (slow) reaction, the triiodide ion is produced:

H₂O₂ + 3 I^– + 2 H⁺ ? I₃^– + 2 H₂O

In the second (fast) reaction, triiodide is reconverted to iodide by the thiosulfate.

I₃^– + 2 S₂O₃^2- ? 3 I^– + S₄O₆^2-

After some time the solution always changes color to a very dark blue, almost black (the solution changes color due to the triiodide-starch complex).

Let’s get started! Rinse everything out very thoroughly with water three times, to ensure that nothing is contaminated before the experiment so you can get a clean start. You can use droppers or measuring spoons (dedicated just to chemistry, not used for cooking) to measure your chemicals. For droppers, make sure you’re using one dropper per chemical, and leave the dropper in the chemical when not in use to decrease the chances of cross-contamination.

Measure out 1 cup of distilled water and pour it into your first cup. Add ½ teaspoon sodium thiosulfate and stir until all the crystals are dissolved. Touch the cup to feel the temperature change. Is it hotter or colder?

Measure out 1 cup of distilled water into a new container. Drop in the starch packing peanut and stir it around until it dissolves. Packing peanuts can be made of cornstarch (as yours is, which is why it “melts” in water) or polystyrene (which melts in acetone, not water).

Into a third cup, measure out 1 cup of hydrogen peroxide.

Into the fourth cup, measure out 1 cup of distilled white vinegar.

Fill your plastic test tube with three parts starch (packing peanut) solution. Add two parts distilled vinegar and two parts potassium iodide. (Make sure you don’t cross-contaminate your chemicals — use clean measuring equipment each time.) Your solution should be clear.

Into another plastic test tube, measure out three parts starch solution. Add two parts hydrogen peroxide and two parts sodium thiosulfate solution. If the solution in the test tube is clear, you’re ready to move on to the next step.

Your next step is to pour one solution into the other and cap it, rocking it gently to mix the solution. While you’re doing this, have someone clock the time from when the two solutions touch to when you see a major change.

What’s going on? There are actually two reactions going on at the same time. When you combined the two solutions, the hydrogen peroxide (H₂O₂) combines with the iodide ions (I) to create triiodide (I₃) and water (H₂O). The sodium thiosulfate (S₂O₃²) grabs the triiodide to form iodine, which is clear. But the sodium thiosulfate eventually runs out, allowing the triiodide to accumulate (indicated by the solution changing color). The time you measure is actually the time it takes to produce slightly more iodide ions than the sodium thiosulfate can wipe out.

By accelerating the first reaction, you can shorten the time it takes the solution to change color. There are a few ways to do this: You can decrease the pH (increasing H+ concentration), or increase the iodide or hydrogen peroxide. To lengthen the time delay, add more sodium thiosulfate.

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Rusty Balloon

Friday January 1, 2010

Mars is coated with iron oxide, which not only covers the surface but is also present in the rocks made by the volcanoes on Mars.

Today you get to perform a chemistry experiment that investigates the different kinds of rust and shows that given the right conditions, anything containing iron will eventually break down and corrode. When iron rusts, it’s actually going through a chemical reaction: Steel (iron) + Water (oxygen) + Air (oxygen) = Rust
Materials

Four empty water bottles
Four balloons
Water
Steel wool
Vinegar
Water
Salt

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Download Student Worksheet & Exercises

This lab is best done over two consecutive days. Plan to set up the experiment on the first day, and finish up with the observations on the next.
Line up four empty bottles on the table.
Label your bottles so you know which is which: Water, Water + Salt, Vinegar, Vinegar + Salt
Fill two bottles with water.
Fill two with vinegar.
Add a tablespoon of salt to one of the water bottles.
Add one tablespoon of salt to one of the vinegar bottles.
Stuff a piece of steel wool into each bottle so it comes in contact with the liquid.
Stretch a balloon across the mouth of each bottle.
Let your experiment sit (overnight is best, but you can shorten this a bit if you’re in a hurry).
The trick to getting this one to work is in what you expect to happen. The balloon should get shoved inside the bottle (not expand and inflate!). Check back over the course of a few hours to a few days to watch your progress.
Fill in the data table.

What’s Going On?

Rust is a common name for iron oxide. When metals rust, scientists say that they oxidize, or corrode. Iron reacts with oxygen when water is present. The water can be liquid or the humidity in the air. Other types of rust happen when oxygen is not around, like the combination of iron and chloride. When rebar is used in underwater concrete pillars, the chloride from the salt in the ocean combines with the iron in the rebar and makes a green rust.

Mars has a solid core that is mostly iron and sulfur, and a soft pastel-like mantle of silicates (there are no tectonic plates). The crust has basalt and iron oxide. The iron is in the rocks and volcanoes of Mars, and Mars appears to be covered in rust.

When iron rusts, it’s actually going through a chemical reaction:
Steel (iron) + Water (oxygen) + Air (oxygen) = Rust

There are many different kinds of rust. Stainless steel has a protective coating called chromium (III) oxide so it doesn’t rust easily.

Aluminum, on the other hand, takes a long time to corrode because it’s already corroded — that is, as soon as aluminum is exposed to oxygen, it immediately forms a coating of aluminum oxide, which protects the remaining aluminum from further corrosion.

An easy way to remove rust from steel surfaces is to rub the steel with aluminum foil dipped in water. The aluminum transfers oxygen atoms from the iron to the aluminum, forming aluminum oxide, which is a metal polishing compound. And since the foil is softer than steel, it won’t scratch.

Exercises

Why did one balloon get larger than the rest?
Which had the highest pressure difference? Why?

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Flying Contraptions

Friday January 1, 2010

Mathematically speaking, this particular flying object shouldn't be able to fly. What do you think about that?

Why can this thing fly? It doesn’t even LOOK like a plane! When I teach at the university, this is the plane that mathematically isn’t supposed to be able to fly! There are endless variations to this project—you can change the number of loops and the size of loops, you can tape two of these together, or you can make a whole pyramid of them. Just be sure to have fun!

Find the Center of Pressure (CP) by doing the opposite: Using a blow-dryer set to low-heat so you don’t scorch your airplane, blast a jet of air up toward the ceiling. Put your airplane in the air jet and, using a pencil tip on the top side of your plane, find the point at which the airplane balances while in the airstream. Label this point “CP” for Center of Pressure. (Which one is closest to the nose?)

Besides paying attention to the CG and CP points, aeronautical engineers need to figure out the static and dynamic stability of an airplane, which is a complicated way of determining whether it will fly straight or oscillate out of control during flight. Think of a real airplane and pretend you’ve got one balanced on your finger. Where does it balance? Airplanes typically balance around the wings (the CG point). Ever wonder why the engines are at the front of small airplanes? The engine is the heaviest part of the plane, and engineers use this weight for balance, because the tail (elevator) is actually an upside-down wing that pushes the tail section down during flight.

When we use math to add up the forces (the pull of gravity would be the weight, for example), it works out that there isn’t enough lift generated by thrust to overcome the weight and drag. When I say, “mathematically speaking...” I mean that the numbers don’t work out quite right. When this happens in science for real scientists, it usually means that they don’t fully understand something yet. There are a number of ‘unsolved’ mysteries still in science.. maybe you’ll be able to help us figure them out?

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Star & Planet Trails

Sunday December 13, 2009

These are a set of videos made using planetarium software to help you see how the stars and planets move over the course of months and years. See what you think and tell us what you learned by writing your comments in the box below.

What’s odd about these star trails?

You can really feel the Earth rolling around under you as you watch these crazy star trails.
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Download Student Worksheet & Exercises

Do the planets follow the same arc across the night sky? You bet! All eight planets follow along the same arc that the sun follows, called the ecliptic. Here’s how the planets move across the sky:

Exercises:

If you have constellations on your class ceiling, chart them on a separate page marking the positions of the rocks with X’s.
Tonight, find two constellations that you will chart. Bring them with you tomorrow using the technique outlined above in Experiment.

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Build a REAL Scale Model of the Solar System

Sunday December 13, 2009

Ever wonder exactly how far away the planets really are? Here’s the reason they usually don’t how the planets and their orbits to scale – they would need a sheet of paper nearly a mile long!

To really get the hang of how big and far away celestial objects really are, find a long stretch of road that you can mark off with chalk. We’ve provided approximate (average) orbital distances and sizes for building your own scale model of the solar system.

When building this model, start by marking off the location of the sun (you can use chalk or place the objects we have suggested below as placeholders for the locations). Are you ready to find out what’s out there? Then let’s get started.

Materials:

measuring tape (the biggest one you have)
tape or chalk to mark off the locations
2 grains of sand or white sugar
12″ beach ball
3 peppercorns
golf or ping pong ball
shooter-size marble
2 regular-size marbles

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Download Student Worksheet & Exercises

All distances are measured from the center of the sun. (In some cases, you might just want to use the odometer in your car to help you measure the distance!

Sun (12″ beach ball) at the starting point.

Mercury (grain of sand) is 41 feet from the sun.

Venus (single peppercorn) is 77 feet from the sun.

Earth (single peppercorn) is 107 feet from the sun.

Mars (half a peppercorn) is 163 feet from the sun.

Jupiter (golf or ping pong ball) is 559 feet from the sun.

Saturn (shooter-size marble) is 1,025 feet from the sun.

Uranus (regular-size marble) is 2,062 feet from the sun.

Neptune (regular marble) is 3,232 feet from the sun.

Pluto (grain of sand) is 4,248 feet from the sun.

Nearest Star (Alpha Centauri) is 5500 miles from the sun.

Is Your Solar System Too Big?

If these distances are too large for you, simply shrink all objects to the size of the period at the end of this sentence and you’ll get your solar system to fit inside your house using these measurements below.

First, draw a tiny dot for the Sun. The diameter of the sun for this scale model is 0.1″, but we’re going to ignore this and all other planet diameters so we can fit this model within a 35′ scale.

We’re going to ignore the sizes of the planets and just focus on how far apart everything is. All distances listed below are measured from the sun. Start by marking off the position of the sun with the tip of a sharp pencil.

Here are the rest of the distances you need to mark off:

Mercury is 4 inches from the sun.

Venus is 7.75 inches from the sun.

Earth is 10 inches from the sun.

Mars is 1′ 4″ from the sun.

Jupiter is 4′ 8″ from the sun.

Saturn is 8′ 6.5″ from the sun.

Uranus is 17′ 2″ from the sun.

Neptune is 26′ 11″ from the sun.

Pluto is 35′ 5″ from the sun.

Our nearest star, Alpha Centauri, is approximately 46 miles from the sun.

Did You Notice…?

Are you mind-boggled yet? Did you notice how the solar system is really just ’empty space’? Our models shown here are too small to start bringing in the moons, but you can see why posters showing the planets are not drawn to scale. What are your thoughts on this experiment? Tell us in the comment area below!

For Advanced Students:

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If you really want to play with the different distances on your own, use this orbital calculator online to help convert the distances for you.

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Solar System Treasure Hunt

Sunday December 13, 2009

After you've participated in the Planetarium Star Show (either live or by listening to the MP3 download), treat your kids to a Solar System Treasure Hunt! You'll need some sort of treasure (I recommend astronomy books or a pair of my favorite binoculars, but you can also use 'Mars' candy bars or home made chocolate chip cookies (call them Galaxy Clusters) instead.

You can print out the clues and hide these around your house on a rainy day. Did you know that I made these clues up myself as a refresher course after the astronomy presentation? Enjoy!

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Astronomy Clues
Click here to download the PDF version or the Word DOC version.

Download Student Worksheet & Exercises

You can print out images of each planet and match them up with the clues indicated below. Post images of each of the planets along with the clue for the next one to really make this an out-of-this-world experience!

The Sun (CLUE #1): Hand this one to the kids to get started.

This object is hot, but not on fire.
Explore the dryer but don’t perspire!

Mercury (CLUE #2): Hide this clue below in the dryer.

This planet is closest, but not the hottest.
Check the sock drawer, and don’t be modest!

Venus (CLUE #3): Hide this clue below in the sock drawer.

This planet is so hot it can melt a cannonball,
Crush spaceships, rain acid, and is in tree tall.

Earth (CLUE #4): Hide this clue below in a tree (or plant).

Most of this planet is covered with water.
Visit the bathtub without making it hotter.

Mars (CLUE #5): Hide this clue below in the bathtub.

This planet is basically a rusty burp.
Discover the refrigerator and take a slurp.

Jupiter (CLUE #6): Hide this clue below next to the milk.

A planet so large it can hold the rest,
Explore our library with infinite zest!

Saturn (CLUE #7): Hide this clue below with a stack of books.

This planet had rings, but not made of gold.
Explore near the front door like an astronaut bold!

Uranus (CLUE #8): Hide this clue below on the front door.

Smacked so hard it now rolls on its side,
Find the window that is ever so wide.

Neptune (CLUE #9): Hide this clue below by sticking it on a window.

Check the sink for hurricane,
gigantic blue farts, and diamond rain.

Pluto (CLUE #10): Hide this clue below near the sink with the TREASURE!

Instead of one there were two, then four…
Visit the mailbox for the one that is no more.

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How to View the Sun Safely

Sunday December 13, 2009

You know you're not supposed to look at the sun, so how can you study it safely? I'm going to show you how to observe the sun safely using a very inexpensive filter. I actually keep one of these in the glove box of my car so I can keep track of certain interesting sunspots during the week!

The visible surface of the sun is called the photosphere, and is made mostly of plasma (remember the grape experiment?) that bubbles up hot and cold regions of gas. When an area cools down, it becomes darker (called sunspots). Solar flares (massive explosions on the surface), sunspots, and loops are all related the sun’s magnetic field. While scientists are still trying to figure this stuff out, here’s the latest of what they do know...

The sun is a large ball of really hot gas - which means there are lots of naked charged particles zipping around. And the sun also rotates, but the poles and the equator move and different speeds (don’t forget – it’s not a solid ball but more like a cloud of gas). When charged particles move, they make magnetic fields (that’s one of the basic laws of physics). And the different rotation rates allow the magnetic fields to ‘wind up’ and cause massive magnetic loops to eject from the surface, growing stronger and stronger until they wind up flipping the north and south poles of the sun (called ‘solar maximum’). The poles flip every eleven years.

There have been several satellites specially created to observe the sun, including Ulysses (launched 1990, studied solar wind and magnetic fields at the poles), Yohkoh (1991-2001, studied x-rays and gamma radiation from solar flares), SOHO (launched 1995, studies interior and surface), and TRACE (launched 1998, studies the corona and magnetic field).

Ok - so back to observing the sun form your own house. Here's what you need to do:

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Materials:

Baader filter film
set of eyeballs

Click here for an inexpensive Baader filter film. You can use these with your naked eye or over the OPEN END (not the eyepeice) of a telescope. See image below:

Want to see a BIG solar flare?
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Retrograde Motion

Sunday December 13, 2009

If you watch the moon, you’d notice that it rises in the east and sets in the west. This direction is called ‘prograde motion’. The stars, sun, and moon all follow the same prograde motion, meaning that they all move across the sky in the same direction.

However, at certain times of the orbit, certain planets move in ‘retrograde motion’, the opposite way. Mars, Venus, and Mercury all have retrograde motion that have been recorded for as long as we’ve had something to write with. While most of the time, they spend their time in the ‘prograde’ direction, you’ll find that sometimes they stop, go backwards, stop, then go forward again, all over the course of several days to weeks.

Here are videos I created that show you what this would look like if you tracked their position in the sky each night for an year or two.

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Mercury and Venus Retrograde Motion

This is a video that shows the retrograde motion of Venus and Mercury over the course of several years. Venus is the dot that stays centered throughout the video (Mercury is the one that swings around rapidly), and the bright dot is the sun. Note how sometimes the trace lines zigzag, and other times they loop. Mercury and Venus never get far from the sun from Earth’s point of view, which is why you’ll only see Mercury in the early dawn or early evening.

Retrograde Motion of Mars

You’ve probably heard of epicycles people used to use to help explain the retrograde motion of Mars. Have you ever wondered what the fuss was all about? Here’s a video that traces out the path Mars takes over the course of several years. Do you see our Moon zipping by? The planets, Sun, and Moon all travel along line called the ‘ecliptic’, as they all are in about the same plane.

Download Student Worksheet & Exercises

Exercises

During which of the months does Mars appear to move in retrograde?
Why does Mars appear to move backward?
Which planets have retrograde motion?

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Air Horns & Sonic BOOM!

Sunday November 29, 2009

Sound can change according to the speed at which it travels. Another word for sound speed is pitch. When the sound speed slows, the pitch lowers. With clarinet reeds, it’s high. Guitar strings can do both, as they are adjustable. If you look carefully, you can actually see the low pitch strings vibrate back and forth, but the high pitch strings move so quickly it’s hard to see. But you can detect the effects of both with your ears.

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The range of your ears is about 20 – 20,000 Hz (cycles per second). Bats and dogs can hear a lot higher than we can. The image (right) is a real picture of an aircraft as it breaks the sound barrier – meaning that the aircraft is passing the speed that sounds travels at (about 700 mph). The white cloud you see in the photo is related to the shock waves that are forming around the craft as it moves into supersonic speeds. You can think of a shock wave as big pressure front, which creates clouds. In this photo, the pressure from the shock waves is condensing the water vapor in the air.

There are lots of things on earth that break the sound barrier – bullets and bullwhips, for example. The loud crack from a whip is the tip zipping faster than the speed of sound.

So why do we hear a boom at all? Sonic booms are created by air pressure (think of how the water collects at the bow of a boat as it travels through the water). The vehicle pushes air molecules aside in such a way they are compressed to the point where shock waves are formed. These shock waves form two cones, at the nose and tail of the plane. The shock waves move outward and rearward in all directions and usually extend to the ground.

As the shock cones spread across the landscape along the flightpath, they create a continuous sonic boom. The sharp release of pressure, after the buildup by the shock wave, is heard as the sonic boom.

How to Make an Air Horn

Let’s learn how to make loud sonic waves… by making an air horn. Your air horn is a loud example of how sound waves travel through the air. To make an air horn, poke a hole large enough to insert a straw into the bottom end of a black Kodak film canister. (We used the pointy tip of a wooden skewer, but a drill can work also.) Before you insert the straw, poke a second hole in the side of the canister, about halfway up the side.

Here’s what you need:

7-9″ balloon
straw
film canister
drill and drill bits

Grab an un-inflated balloon and place it on your table. See how there are two layers of rubber (the top surface and the bottom surface)? Cut the neck off a balloon and slice it along one of the folded edges (still un-inflated!) so that it now lays in a flat, rubber sheet on your table.

Drape the balloon sheet over the open end of the film canister and snap the lid on top, making sure there’s a good seal (meaning that the balloon is stretched over the entire opening – no gaps). Insert the straw through the bottom end, and blow through the middle hole (in the side of the canister).

You’ll need to play with this a bit to get it right, but it’s worth it! The straw needs to *just* touch the balloon surface inside the canister and at the right angle, so take a deep breath and gently wiggle the straw around until you get a BIG sound. If you’re good enough, you should be able to get two or three harmonics!

Download Student Worksheet & Exercises

Troubleshooting: Instead of a rubber band vibrating to make sound, a rubber sheet (in the form of a cut-up balloon) vibrates, and the vibration (sound) shoots out the straw. This is one of the pickiest experiments – meaning that it will take practice for your child to make a sound using this device. The straw needs to barely touch the inside surface of the balloon at just the right angle in order for the balloon to vibrate. Make sure you’re blowing through the hole in the side, not through the straw (although you will be able to make sounds out of both attempts).

Here’s a quick video where you can hear the small sonic boom from a bull whip:

Since most of us don’t have bull whips, might I recommend a twisted wet towel? Just be sure to practice on a fence post, NOT a person!

Exercises

Why do we use a straw with this experiment?
Does the length of the straw matter? What will affect the pitch of this instrument?

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The Best Parent-Annoyer Ever

Sunday November 29, 2009

This is one of my absolute favorites, because it’s so unexpected and unusual… the setup looks quite harmless, but it makes a sound worse than scratching your nails on a chalkboard. If you can’t find the weird ingredient, just use water and you’ll get nearly the same result (it just takes more practice to get it right). Ready?

NOTE: DO NOT place these anywhere near your ear… keep them straight out in front of you.

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Here’s what you need:

water or violin rosin
string
disposable plastic cup
pokey-thing to make a hole in the cup

Download Student Worksheet & Exercises

Exercises

What does the rosin (or water) do in this experiment?
What is vibrating in this experiment?
What is the cup for?

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Seeing Sound Waves

Sunday November 29, 2009

This section is actually a collection of the experiments that build on each other. We’ll be playing with sound waves, and the older students will continue on after this experiment to build speakers.

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Here’s what you need:

a radio or some sort of music player
a balloon
a mixing bowl
water
your parent’s permission

Download Student Worksheet & Exercises

1. Turn on your music player and turn it up fairly loud. (Tell your parents that it’s for science!)

2. Take a look at your speaker. You should be able to see it vibrating. If there’s a song with a lot of bass, you should really be able to see it moving.

3. Put your hand on the speaker. Can you feel the vibrations?

4. ASK YOUR PARENTS if you can carefully put a half-filled bowl of water on top of your speaker. You should be able to see the water vibrate.

Remember that sound is nothing more than vibrating molecules. All speakers do is get molecules of air to vibrate, creating longitudinal waves. They push air. Your eardrums vibrate just like the speakers do when the longitudinal waves of sound energy hit your ears.

How to Feel the Beat

1. Inflate the balloon. Get it fairly large.

2. Turn the music on loud (the more bass the better).

3. Put both hands lightly on the balloon.

4. Walk around the room holding the balloon lightly between your hands.

5. Try to feel the balloon vibrating.

6. Does the balloon vibrate more for low sounds or high sounds?

7. If you have a synthesizer (piano keyboard) you may want to try turning it up a bit and playing one note at a time. You should notice that the balloon vibrates more or less as you go up and down the musical scale. At very high notes, your balloon may not vibrate at all. We’ll talk more about why this happens later.

What’s causing the balloon to vibrate? Energy. Energy causes objects to move a distance against a force. The sound energy coming from the speakers is causing the balloon to vibrate. Your ear drums move in a very similar way to the balloon. Your ear drum is a very thin membrane (like the balloon) that is moved by the energy of the sound. Your ear drum, however, is even more sensitive to sounds than the balloon which is why you can hear sounds when the balloon is not vibrating. If you ear drum doesn’t vibrate, you don’t hear the sound.

What to do this experiment but no speakers?

Here’s another version of the same idea – I’ll bet you did this experiment when you were a small baby! You need: a mixing bowl (one of those metal bowls), something to hit it with ( a wooden spoon works well), and water.

1. Take the mixing bowl and put it on the table.

2. Smack it with the wooden spoon.

3. Listen to the sound.

4. Put your ear next to the bowl and try to hear how long the sound continues.

5. Now hit the bowl again.

6. Touch the bowl with your hand a second or two after you hit it. You should hear the sound stop. This is called dampening.

7. Now, for fun, fill the bowl with water up to an inch or so from the top.

8. Smack the bowl again and look very carefully at where the bowl touches the water.

9. When you first hit the bowl, you should see very small waves in the water.

I want you to notice two things here. Sound is vibration. When the bowl is vibrating, it’s making a sound. When you stop it from vibrating, it stops making sound. Any sound you ever hear, comes from something that is vibrating. It may have vibrated once, like a balloon popping. Or it may be vibrating consistently, like a guitar string.

The other thing I want you to notice is that you can actually see the vibrations. If you put water in the bowl, the tiny waves that are formed when you first hit the bowl are caused by the vibrating sides of the bowl. Those same vibrations are causing the sound that you hear.

If your mom’s worried about making a mess with water (and it’s not bath night tonight) then try this alternate experiment: you’ll need a mixing bowl, wooden spoon, and rubber bands.

1. Stretch a few rubber bands around the box or the bowl. If possible, use different thicknesses of rubber bands.

2. Strum the rubber bands.

3. Feel free to adjust how stretched the bands are. The more stretched, the higher the note.

4. Try plucking a rubber band softly.

5. Now pluck it fairly hard. The hard pluck should be louder.

Again I’d like you to notice three things here. Just like the last experiment, you should see that the sound is coming from the vibration. As long as the rubber band vibrates, you hear a sound. If you stop the rubber band from vibrating, you will stop the sound. Sound is vibration.

The second thing I’d like you to notice is that the rubber bands make different pitched sounds. The thinner the rubber band, or the tighter it’s stretched, the faster it vibrates. Another way to say “vibrating faster” is to say higher frequency. In sound, the higher the frequency of vibration, the higher the pitch of the note. The lower the frequency, the lower the pitch of the note. The average human ear can hear sound at as high a frequency as 20,000 Hz, and as low as 20 Hz. Pianos, guitars, violins and other instruments have strings of various sizes so that they can vibrate at different frequencies and make different pitched sounds. When you talk or sing, you change the tension of your vocal cords to make different pitches.

One last thing to notice here is what happened when you plucked the rubber band hard or softly. The rubber band made a louder noise the harder you plucked it right? Remember again that sound is energy. When you plucked that rubber band hard, you put more energy into it than when you plucked it softly. You gave energy (moved the band a distance against a force) to the rubber band. When you released the rubber band, it moved the air against a force which created sound energy. For sound, the more energy it has, the louder it is. Remember when we talked about amplitude a few lessons back? Amplitude is the size of the wave. The more energy a wave has the bigger it is. When it comes to sound, the larger the wave (the more energy it has) the louder it is. So when you plucked the rubber band hard (gave it lots of energy), you made a louder sound.

I said this in the beginning but I’ll repeat it here, hoping that now it makes more sense. When something vibrates, it pushes particles against a force (creates energy). These pushed particles create longitudinal waves. If the longitudinal waves have the right frequency and enough energy (loudness), your ear drum antennas will pick it up and your brain will translate the energy into what we call sound.

Exercises

What is sound?
How does the rubber band make different sounds?
What difference does it make how hard or soft you pluck the rubber bands?

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Humming Balloon

Sunday November 29, 2009

You can easily make a humming (or screaming!) balloon by inserting a small hexnut into a balloon and inflating. You can also try pennies, washers, and anything else you have that is small and semi-round. We have scads of these things at birthday time, hiding small change in some and nuts in the others so the kids pop them to get their treasures. Some kids will figure out a way to test which balloons are which without popping… which is what we’re going to do right now.

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Here’s what you need:

hexnut
balloon
your lungs

Download Student Worksheet & Exercises

What to do: Place a hexnut OR a small coin in a large balloon. Inflate the balloon and tie it. Swirl the balloon rapidly to cause the hexnut or coin to roll inside the balloon. The coin will roll for a very long time on the smooth balloon surface. At high coin speeds, the frequency with which the coin circles the balloon may resonate with one of the balloon’s “natural frequencies,” and the balloon may hum loudly.

Exercises

How does sound travel?
What is pitch?
How is frequency related to pitch?

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Good Old Telephone

Sunday November 29, 2009

This is the experiment that all kids know about… if you haven’t done this one already, put it on your list of fun things to do. (See the tips & tricks at the bottom for further ideas!)

We’re going to break this into two steps – the first part of the experiment will show us why we need the cups and can’t just hook a string up to our ear. Are you ready?

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You need:

Table
Spoon (or whatever is handy)
Partner

1. Sit at a table.

2. Have your partner sit at the other end of the table.

3. Have your partner very lightly scratch the table with the spoon.

4. Listen to see if you can hear it.

5. While your partner is scratching, put your ear on the table. Do you hear a difference in the sound?

6. Switch roles so your partner gets a chance to try.

Did you notice how you could hear the soft spoon-scratching sound (I love a good alliteration) quite clearly when your head was on the table? The sound waves moved quickly through the table so they lost little of the loudness and quality of the original sound. When sound travels through the air, the sound energy gets dispersed (spread out) much more than through the table, so the sound does not travel as far nor as clearly. This next one is an oldie but a goodie!

A Couple Cups of Conversation

1. Using the scissors or a nail poke a hole in the middle of the bottom of both cups. Get an adult to help you with this. Since this isn’t biology, no bleeding allowed!

2. Thread an end of the string through the hole in the bottom of the cup and tie a big knot in it to keep it from sliding through the hole.

3. Do the same thing with the other cup so that when you are done you have a cup attached to both ends of the string.

4. Take one of the cups for yourself and hand the other cup to your partner. Walk apart from one another until the string is fairly taut.

5. Have your partner hold the cup up to his or her ear while you whisper into your cup.

6. Can your partner hear you? If not, see if you can stretch the string a little more.

7. Switch roles and try again.

The string being a solid and having tightly packed molecules allows the sound wave to move quickly and clearly through it. You can talk very quietly in one cup and yet your partner can still hear you fairly well.

Tips & Tricks

You can try different types of cups (foam, plastic, metal (like tin foil), paper…) and also change the sizes of the cups – is bigger or smaller better? You can also change the connection between the cups – have you tried yarn, wool, string, nylon fishing line, rope, clothesline, or a braided combination? You can also stick a slinky in place of the string of ‘space phones’.

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Seeing Sound Waves using Light

Sunday November 29, 2009

After you’ve completed this experiment, you can try making your own sound-to-light transformer as shown below. Using the properties of sound waves, we’ll be able to actually see sound waves when we aim a flashlight at a drum head and pick up the waves on a nearby wall.

Here’s what you need:

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empty soup can
balloon
small mirror
tape
scissors
hot glue gun
laser or flashlight

You will be adjusting the length of string of a pendulum until you get a pendulum that has a frequency of .5 Hz, 1 Hz and 2 Hz. Remember, a Hz is one vibration (or in this case swing) per second. So .5 Hz would be half a swing per second (swing one way but not back to the start). 1 Hz would be one full swing per second. Lastly, 2 Hz would be two swings per second. A swing is the same as a vibration so the pendulum must move away from where you dropped it and then swing back to where it began for it to be one full swing/vibration.

The following information is for students in our upper level part of the science program:

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“Advanced students: Download your Seeing Sound Waves using Light

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What is Frequency?

Sunday November 29, 2009

In this experiment you will be adjusting the length of string of a pendulum until you get a pendulum that has a frequency of .5 Hz, 1 Hz and 2 Hz. Remember, a Hz is one vibration (or in this case swing) per second. So .5 Hz would be half a swing per second (swing one way but not back to the start). 1 Hz would be one full swing per second. Lastly, 2 Hz would be two swings per second. A swing is the same as a vibration so the pendulum must move away from where you dropped it and then swing back to where it began for it to be one full swing/vibration.

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You’ll need:

3 Foot Long String
A Weight that can be tied to the end of the string
A Timer or Stopwatch
Masking Tape
A Table or Chair
A Partner is helpful

“Advanced students: Download your What is Frequency?”

1. Tie your weight (the official name of the weight on the end is bob. Personally I’ve always preferred the name Shirley, but Bob it is.) to the end of the 3 foot string. If you’ve done the gravity lesson in the Mechanics set of lessons you’ll remember that the weight of the bob doesn’t matter. Gravity accelerates all things equally, so your pendulum will swing at the same speed no matter what the weight of the bob.

2. Tape the string to a table or chair or door jam. Make sure it can swing freely at about 3 feet of length.

3. I would recommend starting with 1 Hz. It tends to be the easiest to find. Then try .5 Hz and then 2 Hz.

4. The easiest way I’ve found to do this is to start the pendulum swinging and at the same time start the timer. Count how many swings you get in ten seconds.

5. Now, adjust the string. Make it longer or shorter and try again. When you get 10 swings in 10 seconds you got it! That’s one swing per second. You should be able to get quite close to one swing per second which is 1 Hz.

6. Now try to get .5 Hz. In this case you will get 5 swings in ten seconds when you find it. (A little hint, the string is pretty long here.)

7. Now speed things up a bit and see if you can get 2 Hz. Be prepared to count quick. That’s 2 swings a second or 20 swings in 10 seconds! (Another little hint, the string is quite short for this one.)

Did you get all three different frequency pendulums? It takes a while but my classes found it rather fun. You’ve created three different frequencies. 2 Hz being the fastest frequency. That was pretty fast right? Can you imagine something going at 10 Hz? 100 Hz? 1,000,000 Hz? I told you things were moving at outrageous speeds!

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Ear Tricks

Sunday November 29, 2009

Think of your ears as ‘sound antennas’. There’s a reason you have TWO of these – and that’s what this experiment is all about. You can use any noise maker (an electronic timer with a high pitched beep works very well), a partner, a blindfold (not necessary but more fun if you have one handy), and earplugs (or use your fingers to close the little flap over your ear – don’t stick your fingers IN your ears!).

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Here’s what you need:

noisemaker
partner
you
blindforld
earplugs

Download Student Worksheet & Exercises

1. Sit or stand in the middle of a room.

2. Close your eyes or put on the blind fold.

3. Have your partner walk to another part of the room as quietly as possible.

4. Have your partner make the noisemaker make a noise.

5. With your eyes still closed, point to where you think the sound came from.

6. Try it several times and then let your partner have a turn.

How well did you do? Probably pretty well. Your ears are very good at determining where sounds are coming from. The reason your ears are so good at detecting the direction of a sound is due to the fact that sound hits one ear slightly before it hits the other ear. You brain does an amazing bit of quick math to make its best guess as to where the sound is coming from and how far away it is. Let’s do a little more with this.

1. Sit or stand in the middle of a room.

2. Close your eyes or put on the blindfold.

3. Have your partner walk to another part of the room as quietly as possible.

4. Have you partner move the sound maker around the room like before, but this time make sure your partner makes the sound directly in front of you, behind you and over your head as well.

5. With your eyes still closed, point to where you think the sound came from.

6. Try it several times and then let your partner have a turn.

Did you get fooled this time? This works sometimes, but not always. What I hope happened was when the noisemaker was above your head, directly in front of you or directly behind you, you had trouble determining where the sound was coming from. Can you guess why this might have happened? Your ears are placed directly across from one another. If a noise happens directly in front of you, it hits your both ears at the exact same time. Your brain has no clues as to where the sound is coming from if the sound hits both ears at the same time so it makes its best guess. In this case, its best guess may be wrong. Let’s try one more thing here.

1. Sit or stand in the middle of a room.

2. Close your eyes or put on the blindfold.

3. Put an ear plug in one of your ears. If you don’t have one, use your finger to cover your ear. Be very careful not to put your finger into your ear. Just use your finger to cover the hole in your ear.

4. Have your partner walk to another part of the room as quietly as possible.

5. Have your partner make the noisemaker make a noise. This will work best if the noise is not too loud.

6. With your eyes still closed, point to where you think the sound came from.

7. Try it several times and then let your partner try to find the sound.

How did you do with just one ear? Did you get fooled a little more often this time? Your brain has fewer clues to work with so it does the best it can with what it has.

Exercises

How do your two ears work together to determine the location of a sound?
Does it matter what frequency (how high or low) the sound is? Are some frequencies easier to detect than others with only one ear?

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Transverse and Longitudinal Waves

Sunday November 29, 2009

Since we can’t see soundwaves as they move through the air, we’re going to simulate one with rope and a friend. This will let you see how a vibration can create a wave. You’ll need at least 10 feet of rope (if you have 25 or 50 feet it’s more fun), a piece of tape (colored if you have it), a slinky, and a partner. Are you ready?

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1. Give one end of the rope to your partner.

2. Stretch the rope out so that it is a bit slack.

3. Now move your hand up and down. Feel free to do it several times in a row. Your partner should keep his or her hands as still as possible.

4. Watch the waves move from your hand to the other end of the rope.

5. Now let your partner create waves.

6. If you wish, you can try to time your vibrations and create waves with specific frequencies. A frequency of one Hertz is fairly easy to do (one rope shake per second). Can you create rope waves of higher frequencies? You may find that your arm gets tired pretty quickly!

Your hand is the vibrating particle. As your hand vibrated up and down, you moved the particles of the rope up and down. As those particles of rope vibrated, they vibrated the particles next to them. As they vibrated, they vibrated the particles next to them and so on and so forth. So the wave moved from your hand across the room. Did your hands move across the room. Nope, but the wave you created with your vibrating hand did.

This is the way energy travels. Why is the rope wave energy? Because the particles moved a distance against a force. Work was done on the particles. In fact, when you shook the rope, your energy from your body moved across the room with the wave and was transferred (moved to) your partner. Your partner’s hands could feel the energy you put into the rope in the first place. The work you did on the rope was transferred by the rope wave and did work on your partners hand. You have moved energy across the room!

Now… let’s add another element to this experiment…

Transverse Waves

1. Put a piece of (colored if possible) tape in about the middle of the rope.

2. Tie your rope to something or let your friend hold on to one end of it.

3. Now pull the rope so that it is a bit slack but not quite touching the floor.

4. Vibrate your arm. Move your arm up and down once and watch what happens.

5. Now, vibrate your arm a bunch of times (not too fast) and see the results. Notice the action of the tape in the middle of the rope.

What you’ve done is create a transverse wave. With a transverse wave, if the particle (in this case your hand) moves up and down, the wave will move to the left and/or right of the particle. The word perpendicular means that if one thing is up and down, the other thing is left and right. A transverse wave is a wave where the particle moves perpendicular to the medium. The medium is the material that’s in the wave. The medium in this case is the rope.

For example, in a water wave, the medium is the water. Your hand moved up and down, but the wave created by your hand moved across the room, not up. The wave moved perpendicular to the motion of your hand. Did you take a look at the tape? The tape represents a particle in the wave. Notice that it too, was going up and down. It was not moving along the wave. In any wave the particles vibrate, they do not move along the wave.

Longitudinal Waves

Now that you’ve seen a transverse wave, let’s take a look at a longitudinal wave. Here’s what you do:

1. Put a piece of tape on one slinky wire in the middle or so of the slinky.

2. Let your friend hold on to one end of the slinky or anchor the slinky to a chair or table.

3. Now stretch the slinky out, but not too far.

4. Quickly push the slinky toward your friend, or the table, and then pull it back to its original position. Did you see the wave?

5. Now do it again, back and forth several times and watch where the slinky is bunched up and where it’s spread out.

6. Notice the tape. What is it doing?

Here you made a longitudinal wave. A longitudinal wave is where the particle moves parallel to the medium. In other words, your hand vibrated in the same direction (parallel to the direction) the wave was moving in. Your vibrating hand created a wave that was moving in the same direction as the hand was moving in. Did you take a look at the tape? The tape was moving back and forth in the same direction the wave was going.

Do you see the difference between a transverse wave and a longitudinal wave? In a transverse waves the particles vibrate in a different direction (perpendicular) to the wave. In a longitudinal wave the particles vibrate in the same direction (parallel) to the wave.

What’s the Difference between Amplitude and Wavelength?

Here’s an easy way to get a feel for amplitude:

1. Put a piece of tape in about the middle of the rope.

2. Tie your rope to something or let your friend hold on to one end of it.

3. Now pull the rope so that it is a bit slack but not quite touching the floor.

4. Your friend should hold their hands as still as possible.

5. Vibrate your hand but only move it up and down about a foot or so. Have your partner pay attention to how that feels when the wave hits him or her.

6. Now, vibrate your hand but now move it up and down 2 or 3 feet. How does that feel to your partner?

7. Have your partner do the vibrating now and see what you feel.

You created two different amplitude waves. The first wave had a smaller amplitude than the second wave. What you and your partner should have felt was more energy the second time. The wave should have hit your hand with more energy when the wave had more amplitude.

Here’s a great way to visualize wavelength:

1. Tie your rope to something or let your friend hold on to it.

2. Now pull the rope so that it is a bit slack but not quite touching the floor.

3. Your friend should hold their hands as still as possible.

4. Now begin vibrating your hand fairly slowly. In this case, it works better if you move your hand in a circle.

5. Try to make a wavelength with the rope. In other words it will look like you’re playing jump rope.

6. Now try a one and a half wavelengths.

7. Can you get two or more wavelengths? You’ve really got to get your hand moving to get it.

In this image, the left wave is ONE wavelength, the middle is 1.5 wavelegnths, and the right is TWO wavelengths. See the difference?

Did you notice how the frequency of your hand determined the wavelength of the rope? The faster your hand, moved the more wavelengths you could get.
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Building Speakers

Sunday November 29, 2009

Alexander Graham Bell developed the telegraph, microphone, and telephone back in the late 1800s. We'll be talking about electromagnetism in a later unit, but we're going to cover a few basics here so you can understand how loudspeakers transform an electrical signal into sound.

This experiment is for advanced students.We'll be making different kinds of speakers using household materials (like plastic cups, foam plates, and business cards!), but before we begin, we need to make sure you really understand a few basic principles. Here's what you need to know to get started:

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For this experiment to really make sense, you'll need to complete the Telephone and the Seeing Sound Waves Experiments first. This will cover the basic mechanics of sound vibrations and waves.

Let's talk about the telegraph. A telegraph is a small electromagnet that you can switch on and off. The electromagnet is a simple little thing made by wrapping insulated wire around a nail. An electromagnet is a magnet you can turn on and off with electricity, and it only works when you plug it into a battery.

Anytime you run electricity through a wire, you also get a magnetic field. You can amplify this effect by having lots of wire in a small space (hence wrapping the wire around a nail) to concentrate the magnetic effect. The opposite is true also - if you rub a permanent magnet along the length of the electromagnet, you'll get an electric current flowing through the wire. Magnetic fields cause electric fields, and electric fields cause magnetic fields. Got it?

A microphone has a small electromagnet next to a permanent magnet, separated by a thin space. The coil is allowed to move a bit (because it's lighter than the permanent magnet). When you speak into a microphone, your voice sends sound waves that vibrate the coil, and each time the coil moves, it causes an electrical signal to flow through the wires, which gets picked up by your recording system.

A loudspeaker works the opposite way. An electrical signal (like music) zings through the coil (which is also allowed to move and attached to your speaker cone), which is attracted or repulsed by the permanent magnet. The coil vibrates, taking the cone with it. The cone vibrates the air around it and sends sounds waves to reach your ear.

If you placed your hand over the speaker as it was booming out sound, you felt something against your hand, right? That's the sound waves being generated by the speaker cone. Each time the speaker cone moves around, it create a vibration in the air that you can detect with your ears. For deep notes, the cone moves the most, and a lot of air gets shoved at once, so you hear a low note. Which is why you can blow out your speakers if your base is cranked up too much. Does that make sense?

Here's a video to help make sense of all these ideas. One of our scientists, Al, is going to demonstrate how to use a signal generator to drive a speaker at different frequencies. We even brought in specialist (with very good hearing!) to detect the full range of sound and used a special microphone during recording, so you should hear the same thing we did during the testing.

Download Student Worksheet & Exercises

How to Build a Speaker

Here's what you need:

Plates or cups made of foam, paper or plastic
Sheet of copy paper
3 business cards
Magnet wire AWG 28, 30 or 32
2-4 neodymium or similar (rare earth) magnets
Index cards or stiff paper
Plastic disposable cup
Tape
Hot glue gun
Scissors
1 audio plug or other cable that fits into your stereo / mp3 player
2 alligator clip wires

Now you're ready to make your speakers. Note that these speakers are made from cheap materials and are for demonstration purposes only... they do not have an amplifier, so you'll need to place your ear close to the speaker to detect the sound. DO NOT connect these speakers up to your iPOD or other expensive stereo equipment, as these speakers are very low resistance (less than 2 ohms) and can damage your sound equipment if you're not careful. The best source of music for these speakers is an old boom box with a place to plug in your headphones. We'll show you everything in this video:

Sound waves can affect liquids also! Here’s what happens if you run sound waves through a non-newtonian cornstarch solution:

Exercises

Does it matter how strong the magnets are?
What else can you use besides a foam plate?
Which works better: a larger or smaller magnet wire coil?
How can you detect magnetic fields?
How does an electromagnet work?
How does your speaker work?
Is a speaker the same as a microphone?
Does the shape and size of the plate matter? What if you use a plastic cup?

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Catapults

Saturday November 7, 2009

When you drop a ball, it falls 16 feet the first second you release it. If you throw the ball horizontally, it will also fall 16 feet in the first second, even though it is moving horizontally… it moves both away from you and down toward the ground. Think about a bullet shot horizontally. It travels a lot faster than you can throw (about 2,000 feet each second). But it will still fall 16 feet during that first second. Gravity pulls on all objects (like the ball and the bullet) the same way, no matter how fast they go.

What if you shoot the bullet faster and faster? Gravity will still pull it down 16 feet during the first second, but remember that the surface of the Earth is round. Can you imagine how fast we’d need to shoot the bullet so that when the bullet falls 16 feet in one second, the Earth curves away from the bullet at the same rate of 16 feet each second?

Answer: that bullet needs to travel nearly 5 miles per second. (This is also how satellites stay in orbit – going just fast enough to keep from falling inward and not too fast that they fly out of orbit.)

Catapults are a nifty way to fire things both vertically and horizontally, so you can get a better feel for how objects fly through the air. Notice when you launch how the balls always fall at the same rate – about 16 feet in the first second. What about the energy involved?

When you fire a ball through the air, it moves both vertically and horizontally (up and out). When you toss it upwards, you store the (moving) kinetic energy as potential energy, which transfers back to kinetic when it comes whizzing back down. If you throw it only outwards, the energy is completely lost due to friction.

The higher you pitch a ball upwards, the more energy you store in it. Instead of breaking our arms trying to toss balls into the air, let's make a simple machine that will do it for us. This catapult uses elastic kinetic energy stored in the rubber band to launch the ball skyward.

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Here's what you need:

9 tongue-depressor size popsicle sticks
four rubber bands
one plastic spoon
ping pong ball or wadded up ball of aluminum foil (or something lightweight to toss, like a marshmallow)
hot glue gun with glue sticks

Download Student Worksheet & Exercises

What’s going on? We’re utilizing the “springy-ness” in the popsicle stick to fling the ball around the room. By moving the fulcrum as far from the ball launch pad as possible (on the catapult), you get a greater distance to press down and release the projectile. (The fulcrum is the spot where a lever moves one way or the other – for example, the horizontal bar on which a seesaw “sees” and “saws”.)

Troubleshooting: These simple catapults are quick and easy versions of the real thing, using a fulcrum instead of a spring so kids don’t knock their teeth out. After making the first model, encourage kids to make their own “improvements” by handing them additional popsicle sticks, spoons, and glue sticks (for the hot glue guns).

If they get stuck, you can show them how to vary their models: glue a second (or third, fourth, or fifth) spoon onto the first spoon for multi-ammunition throws, increase the number of popsicle sticks in the fulcrum from 7 to 13 (or more?), and/or use additional sticks to lengthen the lever arm. Use ping pong balls as ammo and build a fort from sheets, pillows, and the backside of the couch.

Want to make a more advanced catapult?

This catapult requires a little more time, materials, and effort than the catapult design above, but it's totally worth it. This device is what most folks think of when you say 'catapult'. I've shown you how to make a small model - how large can you make yours?

This project lends itself well to taking data and graphing your results: you and your child can jot down the distance traveled along with time aloft with further calculations for high school students for velocity and acceleration. My university students would also calculate statistics, percent error, and more. My students also mapped out the material properties of the 'cantilevered beam' as well as model the popsicle stick as a spring (to determine the spring constant (k) for your calculations from Hooke's Law). You can take this project as far as you want, depending on the interest and ability of kids.

Materials:

plastic spoon
14 popsicle sticks
3 rubber bands
wooden clothespin
straw
wood skewer or dowel
scissors
hot glue gun

Try different ball weights (ping pong, foil crumpled into a ball, whiffle balls, marshmallows, etc) and chart out the results: make a data table that shows what ball you tried and how far it went. You can also use a stopwatch to time how long your ball was in the air.

You can also graph your results: make a chart where you plot each data point on a graph that has distance on the vertical axis and time on the horizontal axis.

Advanced Teaching Tips: For high school and college-level physics classes, you can easily incorporate these launchers into your calculations for projectile motion. Offer students different ball weights (ping pong, foil crumpled into a ball, and whiffle balls work well) and chart out the results.

Exercises Answer the questions below:

How is gravity related to kinetic energy?
1. Gravity creates kinetic energy in all systems.
2. Gravity explains how potential energy is created.
3. Gravity pulls an object and helps its potential energy convert into kinetic energy.
4. None of the above
If you could use your catapult to launch your ball of foil into orbit, how high would it have to go?
1. Above the atmosphere
2. High enough to slingshot around the moon
3. High enough so that when it falls, the earth curves away from it
4. High enough so that it is suspended in empty space
Where is potential energy the greatest on the catapult?

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Potato Cannon

Saturday November 7, 2009

This experiment is for Advanced Students.There are several different ways of throwing objects. This is the only potato cannon we’ve found that does NOT use explosives, so you can be assured your kid will still have their face attached at the end of the day. (We’ll do more when we get to chemistry, so don’t worry!)

These nifty devices give off a satisfying *POP!!* when they fire and your backyard will look like an invasion of aliens from the French Fry planet when you’re done. Have your kids use a set of goggles and do all your experimenting outside.

Here’s what you need:

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potatoes
an acrylic tube (clear is best so you can see what’s happening inside!)
wooden dowel
washer (this is your ‘hand-saver’)

Where is the potential energy the greatest? How much energy did your spud have at this point? Hmmm… let’s see if we can get a few actual numbers with this experiment. In order to calculate potential energy at the highest point of travel, you’ll need to figure out how high it went.

Here are instructions for making your own height-gauge:

Once you get your height gauge working right, you’ll need to track your data. Start a log sheet in your journal and jot down the height for each launch. Let’s practice a sample calculation:

If you measured an angle of 30 degrees, and your spud landed 20 feet away, we can assume that the spud when highest right in the middle of its flight, which is halfway (10 feet). Use basic trigonometry to find the height 45 degrees up at a horizontal distance ten feet away to get:

height = h = (10′) * (tan 30) = 5.8 feet
(Convert this to meters by: (5.8 feet) * (12 inches/foot) / (39.97 inches/meter) = 1.8 meters)

I measured the mass of my spud to be 25 grams (which is 0.025 kg).

Now, let’s calculate the potential energy:

PE = mgh = (0.025 kg) * (1.8 meters) * (10 m/s²) = 0.44 Joules

How fast was the spud going before it smacked into the ground? Set PE = KE to solve for velocity:

mgh = 0.5 mv² gives v = (2gh)^1/2

Plug in your numbers to get:

v = [(2) * (10) * (1.8)]² = 6 m/s (or about 20 feet per second). Cool!

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P-Shooters

Saturday November 7, 2009

This is a simple, fun, and sneaky way of throwing tiny objects. It’s from one of our spy-kit projects. Just remember, keep it under-cover. Here’s what you need:

a cheap mechanical pencil
two rubber bands
a razor with adult help

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Advanced students: Download your P-Shooter Lab here.

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Bobsleds

Saturday November 7, 2009

Bobsleds use the low-friction surface of ice to coast downhill at ridiculous speeds. You start at the top of a high hill (with loads of potential energy) then slide down a icy hill til you transform all that potential energy into kinetic energy. It’s one of the most efficient ways of energy transformation on planet Earth. Ready to give it a try?

This is one of those quick-yet-highly-satisfying activities which utilizes ordinary materials and turns it into something highly unusual… for example, taking aluminum foil and marbles and making it into a racecar.

While you can make a tube out of gift wrap tubes, it’s much more fun to use clear plastic tubes (such as the ones that protect the long overhead fluorescent lights). Find the longest ones you can at your local hardware store. In a pinch, you can slit the gift wrap tubes in half lengthwise and tape either the lengths together for a longer run or side-by-side for multiple tracks for races. (Poke a skewer through the rolls horizontally to make a quick-release gate.)

Here’s what you need:

aluminum foil
marbles (at least four the same size)
long tube (gift wrapping tube or the clear protective tube that covers fluorescent lighting is great)

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If you’re finding that the marbles fall out before the bobsled reaches the bottom of the slide, you need to either crimp the foil more closely around the marbles or decrease your hill height.

Check to be sure the marbles are free to turn in their “slots” before launching into the tube – if you’ve crimped them in too tightly, they won’t move at all. If you oil the bearings with a little olive oil or machine oil, your tube will also get covered with oil and later become sticky and grimy… but they sure go faster those first few times!

Download Student Worksheet & Exercises

Exercises Answer the questions below:

Potential energy is energy that is related to:
1. Equilibrium
2. Kinetic energy
3. Its system
4. Its elevation
If an object’s energy is mostly being used to keep that object in motion, we can say it has what type of energy?
1. Kinetic energy
2. Potential energy
3. Heat energy
4. Radiation energy
True or False: Energy is able to remain in one form that is usable over and over again.
1. True
2. False

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Roller Coasters

Saturday November 7, 2009

We're going to build monster roller coasters in your house using just a couple of simple materials. You might have heard how energy cannot be created or destroyed, but it can be transferred or transformed (if you haven't that's okay - you'll pick it up while doing this activity).

Roller coasters are a prime example of energy transfer: You start at the top of a big hill at low speeds (high gravitational potential energy), then race down a slope at break-neck speed (potential transforming into kinetic) until you bottom out and enter a loop (highest kinetic energy, lowest potential energy). At the top of the loop, your speed slows (increasing your potential energy), but then you speed up again and you zoom near the bottom exit of the loop (increasing your kinetic energy), and you're off again!

Here's what you need:

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marbles
masking tape
3/4" pipe foam insulation (NOT neoprene and NOT the kind with built-in adhesive tape)

To make the roller coasters, you'll need foam pipe insulation, which is sold by the six-foot increments at the hardware store. You'll be slicing them in half lengthwise, so each piece makes twelve feet of track. It comes in all sizes, so bring your marbles when you select the size. The ¾” size fits most marbles, but if you’re using ball bearings or shooter marbles, try those out at the store. (At the very least you’ll get smiles and interest from the hardware store sales people.) Cut most of the track lengthwise (the hard way) with scissors. You’ll find it is already sliced on one side, so this makes your task easier. Leave a few pieces uncut to become “tunnels” for later roller coasters.

Read for some 'vintage Aurora' video? This is one of the very first videos ever made by Supercharged Science:

Download Student Worksheet & Exercises

Tips & Tricks

Loops Swing the track around in a complete circle and attach the outside of the track to chairs, table legs, and hard floors with tape to secure in place. Loops take a bit of speed to make it through, so have your partner hold it while you test it out before taping. Start with smaller loops and increase in size to match your entrance velocity into the loop. Loops can be used to slow a marble down if speed is a problem.

Camel-Backs Make a hill out of track in an upside-down U-shape. Good for show, especially if you get the hill height just right so the marble comes off the track slightly, then back on without missing a beat.

Whirly-Birds Take a loop and make it horizontal. Great around poles and posts, but just keep the bank angle steep enough and the marble speed fast enough so it doesn’t fly off track.

Corkscrew Start with a basic loop, then spread apart the entrance and exit points. The further apart they get, the more fun it becomes. Corkscrews usually require more speed than loops of the same size.

Jump Track A major show-off feature that requires very rigid entrance and exit points on the track. Use a lot of tape and incline the entrance (end of the track) slightly while declining the exit (beginning of new track piece).

Pretzel The cream of the crop in maneuvers. Make a very loose knot that resembles a pretzel. Bank angles and speed are the most critical, with rigid track positioning a close second. If you’re having trouble, make the pretzel smaller and try again. You can bank the track at any angle because the foam is so soft. Use lots of tape and a firm surface (bookcases, chairs, etc).

Troubleshooting Marbles will fly everywhere, so make sure you have a lot of extras! If your marble is not following your track, look very carefully for the point of departure – where it flies off.

-Does the track change position with the weight of the marble, making it fly off course? Make the track more rigid by taping it to a surface.
-Is the marble jumping over the track wall? Increase your bank angle (the amount of twist the track makes along its length).
-Does your marble just fall out of the loop? Increase your marble speed by starting at a higher position. When all else fails and your marble still won’t stay on the track, make it a tunnel section by taping another piece on top the main track. Spiral-wrap the tape along the length of both pieces to secure them together.

HOT TIPS for ULTRA-COOL PARENTS: This lab is an excellent opportunity for kids to practice their resilience, because we guarantee this experiment will not work the first several times they try it. While you can certainly help the kids out, it’s important that you help them figure it out on their own. You can do this by asking questions instead of rushing in to solve their problems. For instance, when the marble flies off the track, you can step back and say:

“Hmmm… did the marble go to fast or too slow?”

“Where did it fly off?”

“Wow – I’ll bet you didn’t expect that to happen. Now what are you going to try?”

Become their biggest fan by cheering them on, encouraging them to make mistakes, and try something new (even if they aren’t sure if it will work out).

Check out this cool roller coaster from one of our students!

Exercises

What type of energy does a marble have while flying down the track of a roller coaster?
What type of energy does the marble have when you are holding it at the top of the track?
At the top of a camel back hill, which is higher for the marble, kinetic or potential energy?
At the top of an inverted loop, which energy is higher, kinetic or potential energy?

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Mystery Toy

Saturday November 7, 2009

Note: Do the pendulum experiment first, and when you’re done with the heavy nut from that activity, just use it in this experiment.

You can easily create one of these mystery toys out of an old baking powder can, a heavy rock, two paper clips, and a rubber band (at least 3″ x 1/4″). It will keep small kids and cats busy for hours.

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Here’s what you get:

can with a lid
heavy rock or large nut
two paper clips
rubber band

You’ll need two holds punched through your container – one in the lid and the bottom. Thread your rubber band through the heavy washer and tie it off (this is important!). Poke the ends of the rubber band through one of the holes and catch it on the other side with a paper clip. (Just push a paper clip partway through so the rubber band doesn’t slip back through the hole.) Do this for both sides, and make sure that your rubber band is a pulled mildly-tight inside the can. You want the hexnut to dangle in the center of the can without touching the sides of the container.

Download Student Worksheet & Exercises

Now for the fun part… gently roll the can on a smooth floor away from you. The can should roll, slow down, stop, and return to you! If it doesn’t, check the rubber band tightness inside the can.

The hexnut is a weight that twists up the rubber band as the can rolls around it. The kinetic energy (the rolling motion of the can) transforms into potential (elastic) energy stored in the rubber band the free side twists around. The can stops (this is the point of highest potential energy) and returns to you (potential energy is being transformed into kinetic). The farther the toy is rolled the more elastic potential energy it stores.

Exercises

Explain in your own words two types of energy transfer:
True or false: All energy in a system is lost to heat.
1. True
2. False

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Whackapow!

Saturday November 7, 2009

In this experiment, you’re looking for two different things: first you’ll be dropping objects and making craters in a bowl of flour to see how energy is transformed from potential to kinetic, but you’ll also note that no matter how carefully you do the experiment, you’ll never get the same exact impact location twice.

To get started, you’ll need to gather your materials for this experiment. Here’s what you need:

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several balls of different weights no bigger then the size of a baseball (golf ball, racket ball, ping pong ball, marble etc. are good choices)
fill a good size container or mixing bowl with flour or corn starch (or any kind of light powder)
If you’re measuring your results, you’ll also need a tape measure (or yard stick) and a spring scale (or kitchen scale).

Are you ready?

1. Fill the container about 2 inches or so deep with the flour.

2. Weigh one of the balls (If you can, weigh it in grams).

3. Hold the ball about 3 feet (one meter) above the container with the flour.

4. Drop the ball.

5. Whackapow! Now take a look at how deep the ball went and how far the flour spread. (If all your balls are the same size but different weights it’s worth it to measure the size of the splash and the depth the ball went. If they are not, don’t worry about it. The different sizes will effect the splash and depth erratically.

6. Try it with different balls. Be sure to record the mass of each ball and calculate the potential energy for each ball.

Each one of the balls you dropped had a certain amount of potential energy that depended on the mass of the ball and the height it was dropped from. As the ball dropped the potential energy changed to kinetic energy until, “whackapow”, the kinetic energy of the ball collided with and scattered the flour. The kinetic energy of the ball transferred kinetic energy and heat energy to the flour.

For Advanced Students:

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Calculate the gravitational potential energy of the ball. Take the mass of the ball, multiply it by 10 m/s²and multiply that by 1 meter. For example, if your ball had a mass of 70 grams (you need to convert that to kilograms so divide it by 1000 so that would be .07 grams) your calculation would be

PE=.07 x 10 x 1 = .7 Joules of potential energy.

So, how much kinetic energy did the ball in the example have the moment it impacted the flour? Well, if all the potential energy of the ball transfers to kinetic energy, the ball has .7 Joules of kinetic energy.

Create a table in your science journal or use ours. (You’ll need Microsoft Excel to use this file.)

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Ball Bounce

Saturday November 7, 2009

When you toss down a ball, gravity pulls on the ball as it falls (creating kinetic energy) until it smacks the pavement, converting it back to potential energy as it bounces up again. This cycles between kinetic and potential energy as long as the ball continues to bounce.

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But note that when you drop the ball, it doesn’t rise up to the same height again. If the ball did return to the same height, this means you recovered all the kinetic energy into potential energy and you have a 100% efficient machine at work. But that’s not what happens, is it? Where did the rest of the energy go? Some of the energy was lost as heat and sound. (Did you hear something when the ball hit the floor?)

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Elastic Potential Energy

Saturday November 7, 2009

There are many different kinds of potential energy. We’ve already worked with gravitational potential energy, so let’s take a look at elastic potential energy.

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Materials: a rubber band

A simple way to demonstrate elastic energy is to stretch a rubber band without releasing it. The stretch in the rubber band is your potential energy. When you let go of the rubber band, you are releasing the potential energy, and when you aim it toward a wall, it’s converted into motion (kinetic energy).

Here’s another fun example: the rubber band can also show how every is converted from one form to another. If you place the rubber band against a part of you that is sensitive to temperature changes (like a cheek or upper lip), you can sense when the band heats up. Simply stretch and release the rubber band over and over, testing the temperature as you go. Does it feel warmer in certain spots, or in just one location?

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Go Go GO!!

Saturday November 7, 2009

This is a nit-picky experiment that focuses on the energy transfer of rolling cars. You’ll be placing objects and moving them about to gather information about the potential and kinetic energy.

We’ll also be taking data and recording the results as well as doing a few math calculations, so if math isn’t your thing, feel free to skip it.

Here’s what you need:

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a few toy cars (or anything that rolls like a skate)
a board, book or car track
measuring tape

The setup is simple. Here’s what you do:

1. Set up the track (board or book so that there’s a nice slant to the floor).

2. Put a car on the track.

3. Let the car go.

4. Mark or measure how far it went.

Download Student Worksheet & Exercises

As you lifted the car onto the track you gave the car potential energy. As the car went down the track and reached the floor the car lost potential energy and gained kinetic energy. When the car hit the floor it no longer had any potential energy only kinetic.

If the car was 100% energy efficient, the car would keep going forever. It would never have any energy transferred to useless energy. Your cars didn’t go forever did they? Nope, they stopped and some stopped before others. The ones that went farther were more energy efficient. Less of their energy was transferred to useless energy than the cars that went less far.

Where did the energy go? To heat energy, created by the friction of the wheels, and to sound energy. Was energy lost? NOOOO, it was only changed. If you could capture the heat energy and the sound energy and add it to the the kinetic energy, the sum would be equal to the original amount of energy the car had when it was sitting on top of the ramp.

For K-8 grades, click here to download a data sheet.

For Advanced Students, click here for the data log sheet. You’ll need Microsoft Excel to use this file.

Exercises

Where is the potential energy greatest?
Where is the kinetic energy greatest?
Where is potential energy lowest?
Where is kinetic energy lowest?
Where is KE increasing, and PE is decreasing?
Where is PE increasing and KE decreasing?

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Pendulums

Saturday November 7, 2009

This is a very simple yet powerful demonstration that shows how potential energy and kinetic energy transfer from one to the other and back again, over and over. Once you wrap your head around this concept, you'll be well on your way to designing world-class roller coasters.

For these experiments, find your materials:

some string
a bit of tape
a washer or a weight of some kind
set of magnets (at least 6, but more is better)

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Here's what you do:

1. Make the string into a 2 foot or so length.

2. Tie the string to the washer, or weight.

3. Tape the other end of the string to a table.

4. Lift the weight and let go, causing the weight to swing back and forth at the end of the pendulum.

Download Student Worksheet & Exercises

Watch the pendulum for a bit and describe what it’s doing as far as energy goes. Some questions to think about include:

Where is the potential energy greatest?
Where is the kinetic energy greatest?
Where is potential energy lowest?
Where is kinetic energy lowest?
Where is KE increasing, and PE is decreasing?
Where is PE increasing and KE decreasing?
Where did the energy come from in the first place?

Remember, potential energy is highest where the weight is the highest.

Kinetic energy is highest were the weight is moving the fastest. So potential energy is highest at the ends of the swings. Here’s a coincidence, that’s also where kinetic energy is the lowest since the weight is moving the least.

Where’s potential energy the lowest? At the middle or lowest part of the swing. Another coincidence, this is where kinetic energy is the highest! Now, wait a minute...coincidence or physics? It’s physics right?

In fact, it’s conservation of energy. No energy is created or destroyed, so as PE gets lower KE must get higher. As KE gets higher PE must get lower. It’s the law...the law of conservation of energy! Lastly, where did the energy come from in the first place? It came from you. You added energy (increased PE) when you lifted the weight.

(By the way, you did work on the weight by lifting it the distance you lifted it. You put a certain amount of Joules of energy into the pendulum system. Where did you get that energy? From your morning Wheaties!)

Chaos Pendulum

For this next experiment, we'll be using magnets to add energy into the system by having a magnetic pendulum interact with magnets carefully spaced around the pendulum. Watch the video to learn how to set this one up. You'll need a set of magnets (at least one of them is a ring magnet so you can easily thread a string through it), tape, string, and a table or chair. Are you ready?

Exercises

Why can we never make a machine that powers itself over and over again?
1. Energy is mostly lost to heat.
2. Energy is completely used up.
3. Energy is unlimited, but is absorbed by neighboring air molecules.
4. None of these
In the pendulum, as kinetic energy increases, potential energy ______________.
1. Increases
2. Decreases
As potential energy decreases, kinetic energy _________________.
1. Increases
2. Decreases

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Disappearing Foam Cup

Friday October 23, 2009

This is looks like a chemical reaction but it’s not – it’s really just a physical change. It’s a really neat trick you can do for your friends or in a magic show. Here’s how it works:

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Download Student Worksheet & Exercises

You can use styrofoam beads, packing peanuts, styrofoam packing materials, or even a styrofoam cup and place it in your glass jar containing acetone. Styrofoam is made up of polystyrene foam, which is mostly air (that’s why foam is so lightweight). When you add the foam cup to the acetone, you’re removing the air in the foam which makes it look like you’re dissolving this huge amount of cups (you can go through a whole stack with only a cup of acetone).

Why does this work? You are removing the structure that supports the shape of the foam, and are left with only the foam molecules at the bottom of the container (it will look like a blob). Think about a camping tent: when you take away the poles, what happens to the tent? It loses its support structure and collapses down. The same thing is happening to the foam when you place it in the acetone – you are removing the structure that holds the shape. Acetone is found in most nail polish removers.
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Homemade Pulleys

Saturday October 17, 2009

These homemade pulleys work great as long as they glide freely over the coat hanger wire (meaning that if you give them a spin, they keep spinning for a few more seconds). You can adjust the amount of friction in the pulley by adjusting the where the metal wire bends after it emerges from the pulley.

[am4show have='p8;p9;p14;p41;p88;p92;' guest_error='Guest error message' user_error='User error message' ] All you need is a wire coathanger, a thread spool, and a pair of vice grips... and the video below.

Download Student Worksheet

Cut a wire coat-hanger at the lower points (at the base of the triangular shape) and use the hook section to make your pulley. Thread both straight ends through a thread spool, crossing in the middle, and bend wire downwards to secure spool in place. Be sure the spool turns freely. Use hook for easy attachment. (These pulleys work well for the return-pulley system experiment in this section.)
If you still have trouble, you can purchase pulleys from the hardware store, or more inexpensively, from a farm supply store. (We get ours from the chicken coup section – no kidding!) If you really want to go hog-wild with pulleys, get a bunch and clip them onto climbing-rated carabineer. [/am4show]

Return-Mechanism Pulley System

Saturday October 17, 2009

Silly as our application for this experiment may sound, we use this system to keep pens handy near the shopping list on the fridge. It’s saved us from many pen-searches over the years!

We install these at various places around the house (by the telephone, fridge, front door, anywhere that you usually need a pen at the last minute), and have even seen them at the counters of local video-rental stores.

[am4show have='p8;p9;p14;p41;p88;p92;' guest_error='Guest error message' user_error='User error message' ]

Download Student Worksheet

Troubleshooting: It’s important to note that the weight needs to slide freely both up and down the length of the cord (which is why fishing line is a great choice – the surface of the line is very low friction). Another important tip: the weights you use must weigh more than the object at the end of the string plus the force of friction in the lines (and the pulley). Hollow, metal objects work great like nuts (for bolts).

You’ll need to practice to find just the right balance point: where the pen flies up to its resting position when you let go of the pen.

This is a great addition to any tree house or playground structure! Hang a loop of rope from a tree branch (don't forget to thread the pulleys onto the rope before you tie the knot! Connect one pulley to the basket handle made from a circle of short rope. Tie a length of rope to the basket handle, then up through one tree pulley, down through the basket pulley, and up through the second tree pulley. Thread a 6" length of PVC pipe onto the end and tie the rope back onto itself to form a handle.

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Block & Tackle

Saturday October 17, 2009

Simple machines make our lives easier. They make it easier to lift, move and build things. Chances are that you use simple machines more than you think. If you have ever screwed in a light bulb, put the lid on a jam jar, put keys on a keychain, pierced food with a fork, walked up a ramp, or propped open a door, you've made good use of simple machines. A block and tackle setup is also a simple machine.

Block and tackle refers to pulleys and rope (in that order). One kid can drag ten adults across the room with this simple setup – we've done this class lots of times with kids and parents, and it really works! Be careful with this experiment - you'll want to keep your fingers away from the rope and don't pull too hard (kids really get carried away with this one!)

If you haven't already, make sure you try out the broomstick version of this activity first.

[am4show have='p8;p9;p14;p41;p88;p92;' guest_error='Guest error message' user_error='User error message' ] Materials:

Rope
pulleys
chain link fence (or a broom)
three people

Cut off about 12" of rope and circle a loop around a strong support, like a chain link fence. Before you tie a knot, thread three pulleys onto the rope… and now tie it off.

Make another circle of rope and add three more pulleys onto it. Loop the rope over the handle of a mop or broom. Thread the rest of the nylon rope through zigzag fashion first through one pulley on the fence, then through a pulley on the mop, then to an open pulley back on the fence, then another free pulley on the mop, etc… Knot the end of the rope to the mop. You should have one free end of rope left.

Attach a kid to the free end of the rope by adding a handle. You can thread a rope through a 6" piece of PVC pipe and tie the rope back on itself. Attach adults to the mop, holding it straight out in front of their chest. The adults' job is to resist the pull they will feel as the kid pulls with his end of the rope.

Download Student Worksheet [/am4show]

Pull Two Friends with One Hand

Saturday October 17, 2009

We're going to be using pulleys to pull two (or more) kids with one hand. You will be using something called ‘Mechanical Advantage’, which is like using your brains instead of brute strength. When you thread the rope around the broom handles, you use 'mechanical advantage' to leverage your strength and pull more than you normally could handle.

How can you possibly pull with more strength than you have? Easy - you trade ‘force’ for ‘distance’ - you can pull ten people with one hand, but you have to pull ten feet of rope for every one foot they travel.

Here's what you do: [am4show have='p8;p9;p14;p41;p88;p92;' guest_error='Guest error message' user_error='User error message' ]

nylon rope (at least 50')
two strong dowels (like the handle from a broomstick)
friends and you

Download Student Worksheet

Have two people face each other and each hold a smooth pipe or strong dowel (like a mop or broom) horizontally straight out in front of their chest. Tie a length of strong nylon rope (slippery rope works best to minimize friction) near the end of the mop.

Drape the rope over the second handle (broom), loop around the bottom, then back to the top of the broom. You're going to zigzag the rope back and forth between the mop and broom until you have four strings on each handle.

Attach a third person to the free end of the rope. Make a quick handle for a third person: Thread a 6" length of PVC pipe onto the end and tie the rope back onto itself to form a handle.

The two people hold the dowels will not be able to resist the pull you give when pulling on the end of the rope! Be careful with this one - there's a lot of force going through your rope, and that's usually the first thing to break. If everyone pulls gently, you don't have to worry.

Troubleshooting Tip: If you’re finding there’s just too much friction between the rope and the broomstick (meaning that the rope doesn’t slide smoothly over the broom handles, then click here to learn how to upgrade to pulleys. [/am4show]

Simple Pulley Experiments

Saturday October 17, 2009

Are you curious about pulleys? This set of experiments will give you a good taste of what pulleys are, how to thread them up, and how you can use them to lift heavy things.

We'll also learn how to take data with our setup and set the stage for doing the ultra-cool Pulley Lift experiments.

Are you ready? [am4show have='p8;p9;p14;p41;p75;p85;p88;p92;' guest_error='Guest error message' user_error='User error message' ] For this experiment, you will need:

One pulley (from the hardware store... get small ones that spin as freely as possible. You’ll need three single pulleys or if you can find one get a double pulley to make our later experiment easier.)
About four feet of string
2 paper cups
many little masses (about 50 marbles, pennies, washers etc.)
Yardstick or measuring tape
A scale (optional)
2 paper clips
Nail or some sort of sharp pokey thing
Table

Download Student Worksheet & Exercises

“Advanced students: Download your Simple Pulley Experiments

1. Take a look at the video to see how to make your “mass carriers”. Use the nail to poke a hole in both sides of the cup. Be careful to poke the cup...not your finger! Thread about 4 inches of string or a pipe cleaner through both holes. Make sure the string is a little loose. Make two of these mass carriers. One is going to be your load (what you lift) and the other is going to be your effort (the force that does the lifting).

2. Dangle the pulley from the table (check out the picture).

3. Bend your two paper clips into hooks.

4. Take about three feet of string and tie your paper clip hooks to both ends.

5. Thread your string through the pulley and let the ends dangle.

6. Put 40 masses (coins or whatever you’re using) into one of the mass carriers. Attach it to one of the strings and put it on the floor. This is your load.

7. Attach the other mass carrier to the other end of the string (which should be dangling a foot or less from the pulley). This is your effort.

8. Drop masses into the effort cup. Continue dropping until the effort can lift the load.

9. Once your effort lifts the load, you can collect some data. First allow the effort to lift the load about one foot (30 cm) into the air. This is best done if you manually pull the effort until the load is one foot off the ground. Measure how far the effort has to move to lift the load one foot.

10. When you have that measurement, you can either count the number of masses in the load and the effort cup or if you have a scale, you can get the mass of the load and the effort.

11. Write your data into your pulley data table in your science journal.

Double Pulley Experiment

You need:

Same stuff you needed in Experiment 1, except that now you need two pulleys.

1. Attach the string to the hook that’s on the bottom of your top pulley.

2. Thread the string through the bottom pulley.

3. Thread the string up and through the top pulley.

4. Attach the string to the effort.

5. Attach the load to the bottom pulley.

6. Once you get it all together, do the same thing as before. Put 40 masses in the load and put masses in the effort until it can lift the load.

7. When you get the load to lift, collect the data. How far does the effort have to move now in order to lift the load one foot (30 cm)? How many masses (or how much mass, if you have a scale) did it take to lift the load?

8. Enter your data into your pulley table in your science journal.

Triple Pulley Experiment

You Need

Same stuff as before If you have a double pulley or three pulleys you can give this a shot. If not, don’t worry about this experiment.

Do the same thing you did in experiments 1 and 2 but just use 3 pulleys. It’s pretty tricky to rig up 3 pulleys so look carefully at the pictures. The top pulley in the picture is a double pulley.

1. Attach the string to the bottom pulley. The bottom pulley is the single pulley. item8

2. Thread the string up and through one of the pulleys in the top pulley. The top pulley is the double pulley.

3. Take the string and thread it through the bottom pulley.

4. Now keep going around and thread it again through the other pulley in the top (double) pulley.

5. Almost there. Attach the load to the bottom pulley.

6. Last, attach the effort to the string.

7. Phew, that’s it. Now play with it!

Take a look at the table and compare your data. If you have decent pulleys, you should get some nice results. For one pulley, you should have found that the amount of mass it takes to lift the load is about the same as the amount of mass of the load. Also, the distance the load moves is about the same as the distance the effort moves.

All you’re really doing with one pulley, is changing the direction of the force. The effort force is down but the load moves up.

Now, however, take a look at two pulleys. The mass needed to lift the load is now about half the force of the load itself! The distance changed too. Now the distance you needed to move the effort, is about twice the distance that the load moves. When you do a little math, you notice that, as always, work in equals work out (it won’t be exactly but it should be pretty close if your pulleys have low friction).

What happened with three pulleys? You needed about 1/3 the mass and 3 times the distance right? With a long enough rope, and enough pulleys you can lift anything! Just like with the lever, the pulley, like all simple machines, does a force and distance switcheroo.

The more distance the string has to move through the pulleys, the less force is needed to lift the object. The work in, is equal to the work out (allowing for loss of work due to friction) but the force needed is much less.

Exercises Answer the questions below:

What is the load and effort of a pulley? Draw a pulley and label it.
What is the best way to say what a simple machine helps us do?
1. Do work without changing force applied
2. Change the direction or strength of a force
3. Lift heavy shipping containers
4. None of these
Name one other type simple machine and an example:

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Inclined Plane

Saturday October 17, 2009

What’s an inclined plane? Jar lids, spiral staircases, light bulbs, and key rings. These are all examples of inclined planes that wind around themselves. Some inclined planes are used to lower and raise things (like a jack or ramp), but they can also used to hold objects together (like jar lids or light bulb threads).

Here’s a quick experiment you can do to show yourself how something straight, like a ramp, is really the same as a spiral staircase.

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Here’s what you need to find:

sheet of paper
short dowel or cardboard tube from a coat hanger
tape
ruler

Find a short dowel or use a cardboard tube from a coat-hanger. Roll a sheet of paper around the tube beginning at the short side and roll toward the triangle point, keeping the base even as it rolls (in the video, I just rolled it, so only use the dowel if you have trouble keeping it rolled evenly.)

Notice that the inclined plane (hypotenuse) spirals up as a tread as you roll. Remind you of screw threads? Those are inclined planes. If you have trouble figuring out how to do this experiment, just watch the video clip below:

Download Student Worksheet & Exercises

Inclined planes are simple machines. It’s how people used to lift heavy things (like the top stones for a pyramid).

Here’s another twist on the inclined plane: a wedge is a double inclined plane (top and bottom surfaces are inclined planes). You have lots of wedges at home: forks, knives, and nails just name a few.

When you stick a fork in food, it splits the food apart. You can make a simple wedge from a block of wood and drive it under a heavy block (like a tree stump or large book) with a kid on top.

Exercises

What is one way to describe energy?
1. The amount of atoms moving around at any given moment
2. Electrons flowing from one area to another
3. The ability to do work
4. The square root of the speed of an electron
Work is when something moves when:
1. Force is applied
2. Energy is used
3. Electrons are lost or gained
4. A group of atoms vibrate
Name two simple machines:
Name one example of a simple machine:

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First, Second, and Third Class Levers

Saturday October 17, 2009

Parts of the Lever

Levers, being simple machines, have only three simple parts. The load, the effort, and the fulcrum. Let’s start with the load. The load is basically what it is you’re trying to lift. The books in the last experiment where the load. Now for the effort. That’s you. In the last experiment, you were putting the force on the lever to lift the load. You were the effort. The effort is any kind of force used to lift the load. Last for the fulcrum. It is the pivot that the lever turns on. The fulcrum, as we’ll play with a bit more later, is the key to the effectiveness of the lever.

There are three types of levers. Their names are first-class, second-class and third-class. I love it when it’s that simple. Kind of like Dr. Seuss’s Thing One and Thing Two. The only difference between the three different levers is where the effort, load and fulcrum are.

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Are you ready for some ‘vintage Aurora’ video? We thought you’d want to check out one of the first videos she ever made (in her basement with the auto-focus stuck in the ON position). Enjoy!

Download Student Worksheet & Exercises

“Advanced students: Download your First, Second, and Third Class Levers”

First-Class Lever

A first-class lever is a lever in which the fulcrum is located in between the effort and the load. This is the lever that you think of whenever you think of levers. The lever you made in Experiment 1 is a first-class lever. Examples of first-class levers are the see-saw, a hammer (when it’s used to pull nails), scissors (take a look, it’s really a double lever!), and pliers (same as the scissors, a double lever).

First Class Lever Experiment

For this experiment, you’ll need:

A nice strong piece of wood. 3 to 8 feet long would be great if you have it.
A brick, a thick book or a smaller piece of wood (for the fulcrum)
Books, gallons of water or anything heavy that’s not fragile

Be careful with this. Don’t use something that’s so heavy someone will get hurt. Also, be sure not to use something so heavy that you break the wooden lever. Last but not least, be sure to keep your head and face away from the lever. I’ve seen folks push down on the lever and then let go. The lever comes up fast and can pop you pretty hard.

1. Put your fulcrum on the ground.

2. Put your lever on the fulcrum. Try to get your fulcrum close to the middle of the lever.

3. Put some weight on one end of the lever.

4. Now push down on the other side of the lever. Try to remember how hard (how much force) you needed to use to lift the heavy object.

5. Move the fulcrum under the lever so that it is closer to the heavy object.

6. Push down on the other side of the lever again. Can you tell the difference in the amount of force?

7. Move the fulcrum closer still to the heavy object. Feel a difference now?

8. Feel free to experiment with this. Move the fulcrum farther away and closer to the object. What conclusions can you draw?

What you may have found, was that the closer the fulcrum is to the heavy object, the less force you needed to push with to get the object to move. Later we will look at this in greater detail, but first let me tell you about the other types of levers.

Second-Class Lever

The second-class lever is a little strange. In a second-class lever, the load is between the fulcrum and the effort. A good example of this is a wheel-barrow. The wheel is the fulcrum, the load sits in the wheel-barrow bucket and the effort is you. Some more examples would be a door (the hinge is the fulcrum), a stapler, and a nut-cracker.

Second-class Lever Experiment

You need:

A nice strong piece of wood. 3 to 8 feet long would be great if you have it.
A brick, a thick book or a smaller piece of wood (for the fulcrum)
Books, gallons of water or anything heavy that’s not fragile

Again, be careful with this. Don’t use something that’s so heavy someone will get hurt. Also, be sure not to use something so heavy that you break the wooden lever. Last but not least, be sure to keep your head and face away from the lever. I’ve seen folks push down on the lever and then let go. The lever comes up fast and can pop you pretty hard.

1. Put your fulcrum, the book or the brick, whatever you’re using on a nice flat spot.

2. Put the end of your lever on the fulcrum.

3. Put the books or gallon jugs or whatever you’re using for a load, in the middle of the lever.

4. Now, put yourself (the effort) on the opposite end of the lever from the fulcrum.

5. Lift

6. Experiment with the load. Move it towards the fulcrum and lift. Then move it toward the effort and lift. Where is it harder(takes more force) to lift the load, near the fulcrum or far? Where does the load lift the greatest distance, near the fulcrum or far?

Third-Class Lever

This fellow is the oddest of all. The third-class lever has the effort between the load and the fulcrum. Imagine Experiment 1 but this time the fulcrum is at one end of the board, the books are on the other end and you’re in the middle. Kind of a strange way to lift books huh? A few examples of this are tweezers, fishing rods (your elbow or wrist is the fulcrum), your jaw (the teeth crush the load which would be your hamburger), and your arm (the muscle connects between your elbow (fulcrum) and your load( the rest of your arm or whatever you’re lifting)). Your skeletal and muscular system is, in fact, a series of levers!

Third-class Lever Experiment

You need:

A nice strong piece of wood. 3 to 8 feet long would be great if you have it.
A brick, a thick book or a smaller piece of wood (for the fulcrum)
Books, gallons of water or anything heavy that’s not fragile

1. Put your fulcrum on the ground in a nice flat place.

2. Put your lever on the fulcrum so that the fulcrum is at the very end of the lever.

3. Put your load on the lever at the end farthest from the fulcrum.

4. Now, put yourself (the effort) in the middle of the lever.

5. Lift. You may need someone to hold down the lever on the fulcrum

6. Experiment with the effort (you). Move towards the fulcrum and lift the load Then move toward the load and lift. Where is it harder(takes more force) to lift the load, near the fulcrum or far? Where does the load lift the greatest distance, near the fulcrum or far?

We’ve had a lot of fun levering this and levering that but now we have to get to the point of all this simple machine stuff. Work equals force times distance, right? Well, what have you been doing all this time with these levers? You’ve been moving something (the load) a distance against a force (gravity). You’ve been doing work. You’ve been exerting energy. See how it all ties in nicely?

In experiments 1,2 and 3, I wanted you to notice how much force you exerted and how much the load moved. You may have noticed that when the force was small (it was very easy to lift) the load moved a very small distance. On the other hand, when the force was large (hard to lift), the load moved a greater distance. Let me point your attention to one more thing and then we’ll play with this.

When the force used to lift the load was small, you moved the lever a large distance. When the force used to lift the load was great you moved the lever a small distance. Remember, work=force x distance. There is work done on both sides of the lever. The effort (you in this case) pushes the lever a distance against a force…work is done. The load also moves a distance against a force so there too…work is done.

Now, here’s the key to this that I hope you can see in the next experiment. Work in is equal to work out. The work you do on one side of the lever (work in), is equal to the work that happens to the load (work out). Let’s do a quick bit of math for an example. Phillip wants to move a 10 kg (22 lb.)box. He uses a lever and notices that when he lifts the box .1meter (4 inches) he has to push the lever down 1 meter with a force of 1 kg. Now let’s do some math. (Officially we should convert kilograms (a unit of mass) to Newtons (a unit of force) so that we can work in Joules which is a unit of work. However, we’ll do it this way so you can see the relationship more easily.)

Phillip’s work (the work in) = 1 kg x 1 m = 1

Work on the bowling ball (the work out) = 10 kg x .1 m = 1

Work in equals work out! Later in this energy unit, you’ll learn about energy efficiency. At that point, you’ll see that you never get all the energy you want from the energy you put in. Some energy is lost to sound and some to heat. A lever is incredibly efficient but you may still see, in your measurements, that the energy in is greater than the energy you get out.

For Advanced Students:

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Speaking of your measurements…let’s make some. Open up your science journal and record the type of lever, weight, and location information for your different trial runs. Take a look at your data – can you figure out how much weight you’d need to lift your parents?

Let’s see if we can figure this out. For a 10′ long beam with the fulcrum in the exact center, you can lift as much as you weigh. For example, if you weigh 100 pounds, you can lift some sitting on the other end, as long as they weigh 100 pounds or less. If you slide the beam and move the fulcrum so that the longer end is on your side, you can lift more than you weigh.

So if there’s 7 feet of beam on Alice’s side and only 3 feet on Bob’s end, you can easily figure this out with a little math (and principles of torque). Here’s what you do:

(Alice’s Weight) * (Distance from Alice to the Fulcrum) = (Alice’s Lifting Ability) * (Distance from Bob to the Fulcrum)

If Alice weighs 100 pounds and when standing on the 7-foot end of the see-saw, she barely can lift Bob, let’s find out how much Bob weighs.

(100 pounds) (7 feet) = (Alice’s Lifting Ability) * (3 feet)

700 / 3 = Alice’s Lifting Ability, and since she can just barely lift Bob…

Bob weighs 233 pounds!

Now can you figure out how much lever arm distance you need to lift your parents? If Mom and Dad together weigh 300 pounds, and you have a 10′ long beam and you weigh 100 pounds, let’s find the fulcrum distance you’d need to lift them. Let’s put your algebra to use here:

Let’s make ‘x’ the distance from you to the fulcrum. This makes the distance from your parents to the fulcrum 10′ – x. (If you’re 4 feet from the fulcrum, that means your parents are 6′, right?)

(100 pounds) (x) = (300 pounds) (10′ – x)

100 x = 3000 – 300 x

400 x = 3000

x = 3000 / 400

Solve for x and you’ll find that the distance from you to the fulcrum is 7.5 feet!

Exercises Answer the questions below:

What is the best definition for a simple machine?
1. A machine with less than three parts
2. A machine with a simple name
3. A machine that changes the direction or amount of a force
4. A machine that helps you do work quickly
What are the three parts of a lever? Circle all that apply:
1. Fulcrum
2. Weight
3. Load
4. Effort
Name two examples of levers that you could find in your house:
What are the types of levers called?
1. Three tiers
2. First, second, and third class
3. Poor, rich, and middle
4. Forty-five and ninety-nine percenters
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Roller Skate Belts

Saturday October 17, 2009

This isn't strictly a 'levers' experiment, but it's still a cool demonstration about simple machines, specifically how pulleys are connected with belts.

Take a rubber band and a roller skate (not in-line skates, but the old-fashioned kind with a wheel at each corner.) Lock the wheels on one side together by wrapping the rubber band around one wheel then the other. Turn one wheel and watch the other spin.

Now crisscross the rubber band belt by removing one side of the rubber band from a wheel, giving it a half twist, and replacing it back on the wheel. Now when you turn one wheel, the other should spin the opposite direction. Here's a quick video on what to expect:

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Download Student Worksheet [/am4show]

Hydraulic Pneumatic Earth Mover

Saturday October 17, 2009

When people mention the word “hydraulics”, they could be talking about pumps, turbines, hydropower, erosion, or river channel flow. The term “hydraulics” means using fluid power, and deals with machines and devices that use liquids to move, lift, drive, and shove things around.

Liquids behave in certain ways: they are incompressible, meaning that you can’t pack the liquid into a tighter space than it already is occupying.

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If you’ve ever filled a tube partway with water and moved it around, you’ve probably noticed that the water level will remain the same on either side of the tube.

However, if you add pressure to one end of the tube (by blowing into the tube), the water level will rise on the opposite side. If you decrease the pressure (by blowing across the top of one side), the water level will drop on the other side.

In physics, this is defined through Pascal’s law, which tells us how the pressure applied to one surface can be transmitted to the other surface. As liquids can’t be squished, whatever happens on one surface affects what occurs on the other. Examples of this effect include siphons, water towers, and dams. Scuba divers know that as they dive 30 feet underwater, the pressure doubles. This effect is also show in hydraulics – and more importantly, in the project we’re about to do!

But first, let’s understand what’s happening with liquids and pressure:

Here’s an example: If you fill a glass full to the brim with water, you reach a point where for every drop you add on top, one drop will fall out. You simply can’t squish any more water molecules into the glass without losing at least the same amount. Excavators, jacks, and the brake lines in your car use hydraulics to lift huge amounts of weight, and the liquid used to transfer the force is usually oil at 10,000 psi.

Air, however, is compressible. When car tires are inflated, the hose shoves more and more air inside the tire, increasing the pressure (amount of air molecules in the tire). The more air you stuff into the tire, the higher the pressure rises. When machines use air to lift, move, spin, or drill, it’s called “pneumatics”. Air tools use compressed air or pure gases for pneumatic power, usually pressurized to 80-100 psi.

Different systems require either hydraulics or pneumatics. The advantage to using hydraulics lies in the fact that liquids are not compressible. Hydraulic systems minimize the “springy-ness” in a system because the liquid doesn’t absorb the energy being transferred, and the working fluids can handle much heavier loads than compressible gases. However, oil is flammable, very messy, and requires electricity to power the machines, making pneumatics the best choice for smaller applications, including air tools (to absorb excessive forces without injuring the user).

We’re going to build our own hydraulic-pneumatic machine. Here’s what you need to do:

Materials:

plastic cup
20 tongue-depressor-size popsicle sticks
6 syringes (anything in the 3-10mL size range will work)
6 brass fasteners
5’ of flexible tubing (diameter sized to fit over the nose of your syringes)
four wheels (use film canister lids, yogurt container lids, milk jug lids, etc.)
4 rubber bands
two naked (unwrapped) straws
skewers that fit inside your straws
hot glue gun (with glue sticks)
sharp scissors or razor (get adult help)
drill with small drill bits (you’ll be drilling a hole large enough to fit the stem of a brass fastener)

earthmover

Let’s play with these different ideas right now and really “feel” the difference between hydraulics and pneumatics. Connect two syringes with a piece of flexible tubing. Cut the tubing into three equal-sized pieces and use one to experiment with. Shove the plunger on one syringe to the “empty”, and leave the other in the “filled” position before connecting the tubing. What happens when you push or lift one of the plungers? Is it quick to respond, or is there “slop” in the system?

Now remove both plungers and, leaving the tubing attached, fill the system with water to the brim on both ends (this is a good bath-time activity!). Keep the open ends of the syringes at the same level as you fill them. What happens if you lower one of the syringes? What happens when you raise it back up? Is there now air in your system?

Fill your syringe-tube system up with water again, keeping the plungers at the same height as you work. Insert one of the plungers into one of the syringes and play with the levels of the syringes again, lifting one and lowering the other. Now what happens, or doesn’t happen?

Why does that work? Because both syringes are open to the atmosphere, they both have equal amounts of air pressure pushing down on the surface of the water. When you raise one syringe higher than the other, you have increased the elevation head of higher syringe, which works to equalize the water levels in the two syringes (thus shoving water out of the lower syringe). Elevation head is due to the fluid’s weight (gravitational force) acting on the fluid and is related to the potential energy of the raised syringe (which increased with elevation).

Now connect your plungers into a fully hydraulic system: Push the plunger all the way down to expel the water from one of the syringes (water should leak all over the place from the open syringe). Now add the second plunger to the open syringe and push the plunger down halfway. What happens? You have just made a hydraulic system!

Are you ready to build it into a three-axis machine? Then click the play button below:

Download Student Worksheet

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The SeeSaw

Saturday October 17, 2009

We’re going to use everyday objects to build a simple machine and learn how to take data. Sadly, most college students have trouble with these simple steps, so we’re getting you a head start here. The most complex science experiments all have these same steps that we’re about to do… just on a grander (and more expensive) scale. We’re going to break each piece down so you can really wrap your head around each step. Are you ready to put your new ideas to the test?

This experiment is for Advanced Students.

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You need:

A wooden ruler or a paint stick for the lever
Many pennies, quarters, or washers (many little somethings of the same mass)
A spool, eraser, pencil (anything that can be your fulcrum)
A ruler (to be your um….ruler)
Paper cups
Optional: A scale that can measure small amounts of mass (a kitchen scale is good)

Download Student Worksheet & Exercises

1. Tape one paper cup to each end of lever. (This allows for an easy way to hold the pennies on the lever.)

2. Set your fulcrum on the table and put your lever (ruler or paint stick) on top of it. Try to get the ruler to balance on the fulcrum.

3. Put five pennies on one side of your lever.

4. Now, put pennies, one at a time on the other side of your lever, this is your effort. Keep adding pennies until you get your lever to come close to balancing. Try to keep your fulcrum in the same place on your lever. You may even want to tape it there.

5. Count the pennies on the effort side and count the pennies on the load side. If you have a scale, you can weigh them as well. With the fulcrum in the middle you should see that the pennies/mass on both sides of the lever are close to equal.

6. This part’s a little tricky. Measure how high the lever was moved. On the load side, measure how far the lever moved up and on the effort side measure how far the lever moved down. Be sure to do the measuring at the very ends of the lever.

7. Write your results in your science journal as shown in the video.

8. Remove the pennies and do it all over again, this time move the fulcrum one inch (two centimeters) closer to the load side.

9. Continue moving the fulcrum closer to the load until it gets too tough to do. You’ll probably be able to get it an inch or two (two to four centimeters) from the load.

10. If you didn’t use a scale feel free to stop here. Don’t worry about the “work in” and “work out” parts of the table. Take a look at your table and check out your results. Can you draw any conclusions about the distance the load moved, the distance the effort moved, and the amount of force required to move it?

11. If you used a scale to get the masses you can find out how much work you did. Remember that work=force x distance. The table will tell you how to find work for the effort side (work in) and for the load side (work out). You can multiply what you have or if you’d like to convert to Joules, which is a unit of work, feel free to convert your distance measurements to meters and your mass measurements to Newtons. Then you can multiply meters times Newtons and get Joules which is a unit of work.

1 inch = .025 meters

1 cm = .01 meter

1 ounce =0.278 Newtons

1 gram = 0.0098 Newtons

By taking a look at your data and by all the other work we did this lesson, you can see the beautiful switcheroo of simple machines. Simple machines sacrifice distance for force. With the lever, the farther you had to push the lever, the less force had to be used to move the load.

The work done by the effort is the same as the work done on the load. By doing a little force/distance switcheroo, moving the load requires much less force to do the work. In other words, it’s much easier. Anything that makes work easier gets a thumbs up by me! Hooray for simple machines!

Exercises

What is work?
1. Force against an object
2. Force over distance
3. 9 hours and sweat
4. Energy applied to an object
What is the unit we use to measure energy?
1. Newton
2. Watt
3. Joule
4. Horsepower
Describe a first class lever using one example.

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What’s a Joule?

Saturday October 17, 2009

This experiment is for Advanced Students. We’re going to really get a good feel for energy and power as it shows up in real life. For this experiment, you need:

Something that weighs about 100 grams or 4 ounces, or just grab an apple.
A meter or yard stick

This might seem sort of silly but it’s a good way to get the feeling for what a Joule is and what work is.
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Download Student Worksheet & Exercises

1. Grab your 100 gram object, put it on a table.

2. Now lift it off the table straight up until you lift it one meter (one yard).

3. Lift it up and down 20 times.

A 100 gram object takes about one Newton of force to lift. Since it took one Newton of force to lift that object, how much work did we do? Remember work = force x distance so in this case work = 1 Newton x 20 meters or work = 20 Joules.

You may ask “but didn’t we move it 40 meters, 20 meters up and 20 down?” That’s true, but work is moving something against a force. When you moved the object down you were moving the object with a force, the force of gravity. Only in lifting it up, are you actually moving it against a force and doing work. Four Joules are about 1 calories so we did 5 calories of work.

“Wow, I can lift an apple 20 times and burn 5 calories! Helloooo weight loss!” Well…not so fast there Richard Simmons. When we talk about calories in nutrition we are really talking about kilo calories. In other words, every calorie in that potato chip is really 1000 calories in physics. So as far as diet and exercise goes, lifting that apple actually only burned .005 calories of energy,…rats.

It is interesting to think of calories as the unit of energy for humans or as the fuel we use. The average human uses about 2000 calories (food calories that is, 2,000,000 actual calories) a day of energy. Running, jumping, sleeping, eating all uses calories/energy. Running 15 minutes uses 225 calories. Playing soccer for 15 minutes uses 140 calories. (Remember those are food calories, multiply by 1000 to get physics calories). This web site has a nice chart for more information: Calories used in exercise.

Everything we eat refuels that energy tank. All food has calories in it and our body takes those calories and converts them to calories/energy for us to use. How did the food get the energy in it? From the sun! The sun’s energy gives energy to the plants and when the animals eat the plants they get the energy from the sun as well.

So, if you eat a carrot or a burger you are getting energy from the sun! Eating broccoli gives you about 50 calories. Eating a hamburger gives you about 450 calories! We use energy to do things and we get energy from food. The problem comes when we eat more energy than we can use. When we do that, our body converts the energy to fat, our body’s reserve fuel tank. If you use more energy then you’ve taken in, then your body converts fat to energy. That’s why exercise and diet can help reduce your weight.

Let’s take the concept of work a little bit farther. If Bruno carries a 15 pound bowling ball up a 2 meter (6 foot) flight of stairs, how much work does he do on the bowling ball? It takes 66 Newtons of force to lift a 15 pound bowling ball 1 meter. Remember work = force x distance.

So, work = 66 Newtons x 2 meters. In this case, Bruno does 132 Joules of work on that bowling ball. That’s interesting, but what if we wanted to know how hard poor Bruno works? If he took a half hour to go up those stairs he didn’t work very hard, but if he did it in 1 second, well then Bruno’s sweating!

That’s the concept of power. Power is to energy like miles per hour is to driving. It is a measure of how much energy is used in a given span of time. Mathematically it’s Power = work/time. Power is commonly measured in Watts or Horsepower. Let’s do a little math and see how hard Bruno works.

In both cases mentioned above Bruno, does 132 Joules of work, but in the first case he does the work in 30 minutes (1800 seconds) and in the last case he does it in 1 second. Let’s first figure out Bruno’s power in Watts. A Watt is 1 Joule/second so:

For the half hour Bruno’s Power = 132 Joules/1800 seconds = .07 Watts

For the second Bruno’s Power = 132 joules/1 second = 132 Watts

You can see that the faster you exert energy the more power you use. Another term for power is horsepower. You may have heard the term horsepower in car ads. The more powerful car can exert more energy faster, getting the car moving faster. A Dodge Viper has 450 horsepower which can accelerate a 3,300 pound car from 0 to 60 mph in 4.1 seconds…WOW!

One horsepower is 745 Watts or one Watt is .001 horsepower. So converting Watts to horsepower poor Bruno exerts:

.07 x .001 = .00007 horsepower over the half hour

132 x .001 = .132 horsepower over the second (not exactly a Dodge Viper!)

Exercises

If something has a weight of 2 Newtons and is moved half a meter, how many Joules of energy are used? Show your work.
What is the source of all this energy we’re working with here?
It doesn’t count as work when you move the apple back down. Why not?

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Measuring Power

Saturday October 17, 2009

We’re going to practice measuring and calculating real life stuff (because science isn’t just in a textbook, is it?) When I taught engineering classes, most students had never analyzed real bridges or tools before – they only worked from the textbook. So let’s jump out of the words and into action, shall we? This experiment is for Advanced Students.

Before we start, make sure you’ve worked your way through this experiment first!

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For this experiment, you need:

Meter or yard stick
A stopwatch or timer
Object

Here’s what you do:

Download Student Worksheet & Exercises

1. Grab your 100 gram object, put it on a table.

2. Now lift it off the table straight up until you lift it one meter (one yard).

3. Start the timer and at the same time start lifting the object up and down 20 times.

4. Stop the timer when you’re done with the 20 lifts.

So, do you have the power of the Dodge Viper? Hmmm, probably not but let’s take a look.

First of all figure out how much work you did. Work = force x distance so take the force you used and multiply that by the distance you moved it. In this case, you can multiply 1 Newton x 20 meters and get 20 Joules of work.

Now figure out how much power you used. Power is work divided by time so take your work (20 Joules) and divide it by how much time it took you to do that work.

For example, if you lifted the block 20 times (doing 20 Joules of work) in 5 seconds, you did 20 Joules/5 seconds = 4 Watts of power. To convert Watts to horsepower we multiply by .001 so in this example, you did 4 x .001 = .004 horsepower. Not exactly vroom vroom!

Exercises

What is work?
1. Force divided by distance
2. Force times distance
3. Energy required for power
4. Kinetic and potential energy
What is power?
1. Work divided by time
2. Work multiplied by time
3. Energy used in an exercise
4. Calories over time
How do we measure work? Name one unit.
How do we measure power? Name one unit.

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Trebuchet

Saturday October 17, 2009

This experiment is for Advanced Students. For ages, people have been hurling rocks, sticks, and other objects through the air. The trebuchet came around during the Middle Ages as a way to break through the massive defenses of castles and cities. It’s basically a gigantic sling that uses a lever arm to quickly speed up the rocks before letting go. A trebuchet is typically more accurate than a catapult, and won’t knock your kid’s teeth out while they try to load it.

Trebuchets are really levers in action. You’ll find a fulcrum carefully positioned so that a small motion near the weight transforms into a huge swinging motion near the sling. Some mis-named trebuchets are really ‘torsion engines’, and you can tell the difference because the torsion engine uses the energy stored in twisted rope or twine (or animal sinew) to launch objects, whereas true trebuchets use heavy counterweights.

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This is a serious wood-construction project. If you have access to scrap wood and basic tools (and glue!), you have everything you need to build this project. You will need to find heavy objects (like rocks or marbles) for the weights.

We want kids to discover that science isn’t in the special parts that come with a kit, but rather in the imagination and skill of the kid building it. We strive to avoid parts that are specially made just for a kit, molded plastic pieces, etc. and instead use parts that any kid could buy from the store. This means that kids can feel free to change things around, use their own ideas to add improvements and whatever else their imagination can come up with. So on this note, let’s get started.

WARNING: This project requires the use of various hand tools. These tools should only be used with adult supervision, and should not be used by children under 12 years of age.

Tools you’ll need:

Hammer
Electric drill with ¼” bit
Hot glue gun & glue sticks
Measuring tape or ruler
Hand saw & clamp (or miter box)
Scissors
Screwdriver (flathead) or wood chisel

Materials:

7 pieces of ½” x ½” x 24″ pieces of wood stock
2 pieces of ¾” x 24″ wood
1 piece of 3″ x 24″ wood
18″ Wooden dowel
Screw eye
Nails
String
Clear tube
Rubber mesh

Note: wood pieces may be slightly larger or smaller than specified. Just use your best judgment when sizing.

From ½” x ½” x 24″ pieces of wood stock cut:

3 pieces 5″ long
2 pieces 9″ long
3 pieces 3-1/2″ long
4 pieces 5-1/2″ long

From the dowel cut:

2 pieces 7″ long
1 piece 4″ long

From the 3″ x 24″ flat piece of wood cut:

2 pieces 3″ long (one of these has a 1″ square notch in it)
2 pieces 5″ long
1 piece 4-1/2″ long

AND…

String should be cut into 2 pieces 14-16″ long
The pouch is cut from the rubber mesh and is 5″ x 1-1/2″

Advanced Students: Download your Student Worksheet Lab here!

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Electrolysis

Saturday October 10, 2009

This experiment is just for advanced students. If you guessed that this has to do with electricity and chemistry, you’re right! But you might wonder how they work together. Back in 1800, William Nicholson and Johann Ritter were the first ones to split water into hydrogen and oxygen using electrolysis. (Soon afterward, Ritter went on to figure out electroplating.) They added energy in the form of an electric current into a cup of water and captured the bubbles forming into two separate cups, one for hydrogen and other for oxygen.

This experiment is not an easy one, so feel free to skip it if you need to. You don’t need to do this to get the concepts of this lesson but it’s such a neat and classical experiment (my students love it) so you can give it a try if you want to. The reason I like this is because what you are really doing in this experiment is ripping molecules apart and then later crashing them back together.

Have fun and please follow the directions carefully. This could be dangerous if you’re not careful. The image shown here is using graphite from two pencils sharpened on both ends, but the instructions below use wire. Feel free to try both to see which types of electrodes provide the best results.

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You will need:

2 test tubes or thin glass or plastic something closed at one end. I do not recommend anything wider than a half inch in diameter.
2 two wires, one needs to be copper, at least 12 inches long. Both wires need to have bare ends.
1 cup
sodium sulfate OR salt
Water
One 9 volt battery
Long match or a long thin piece of wood (like a popsicle stick) and a match
Rubber bands
Masking tape

Download Student Worksheet & Exercises
1. Fill the cup with water.

2. Put a tablespoon of salt or sodium sulfate into the water and stir it up. (The salt allows the electricity to flow better through the water.)

2. Put one wire into the test tube and rubber band it to the test tube so that it won’t come out (see picture).

3. Use the masking tape to attach both wires to the battery. Make sure the wire that is in the test tube is connected to the negative (-) pole of the battery and that the other is connected to the positive (+) pole. Don’t let the bare parts of the different wires touch. They could get very hot if they do.

4. Fill the test tube to the brim with the salt water.

5. This is the tricky part. Put your finger over the test tube, turn it over and put the test tube, open side down, into the cup of water. (See picture.)

6. Now put the other wire into the water. Be careful not to let the bare parts of the wires touch.

7. You should see bubbles rising into the test tube. If you don’t see bubbles, check the other wire. If bubbles are coming from the other wire either switch the wires on the battery connections or put the wire that is bubbling into the test tube and remove the other. If you see no bubbles check the connections on the battery.

8. When the test tube is half full of gas (half empty of salt water depending on how you look at it) light the long match or the wooden stick. Then take the test tube out of the water and let the water drain out. Holding the test tube with the open end down, wait for five seconds and put the burning stick deep into the test tube (the flame will probably go out but that’s okay). You should hear an instant pop and see a flash of light. If you don’t, light the stick again and try it another time. For some reason, it rarely works the first time but usually does the second or third.

A water molecule, as you saw before, is two hydrogen atoms and one oxygen atom. The electricity encouraged the oxygen to react with the copper wire leaving the hydrogen atoms with no oxygen atom to hang onto. The bubbles you saw were caused by the newly released hydrogen atoms floating through the test tube in the form of hydrogen gas. Eventually that test tube was part way filled with nothing but pure hydrogen gas.

But how do you know which bubbles are which? You can tell the difference between the two by the way they ignite (don’t’ worry – you’re only making a tiny bit of each one, so this experiment is completely safe to do with a grown up).

It takes energy to split a water molecule. (On the flip side, when you combine oxygen and hydrogen together, it makes water and a puff of energy. That’s what a fuel cell does.) Back to splitting the water molecule - as the electricity zips through your wires, the water molecule breaks apart into smaller pieces: hydrogen ions (positively charged hydrogen) and oxygen ions (negatively charged oxygen). Remember that a battery has a plus and a minus charge to it, and that positive and negative attract each other.

So, the positive hydrogen ions zip over to the negative terminal and form tiny bubbles right on the wire. Same thing happens on the positive battery wire. After a bit of time, the ions form a larger gas bubble. If you stick a cup over each wire, you can capture the bubbles and when you’re ready, ignite each to verify which is which.

If the match burns brighter, the gas is oxygen. If you hear a POP!, the gas is hydrogen. Oxygen itself is not flammable, so you need a fuel in addition to the oxygen for a flame. In one case, the fuel is hydrogen, and hence you hear a pop as it ignites. In the other case, the fuel is the match itself, and the flame glows brighter with the addition of more oxygen.

When you put the match to it, the energy of the heat causes the hydrogen to react with the oxygen in the air and “POP”, hydrogen and oxygen combine to form what? That’s right, more water. You have destroyed and created water! (It’s a very small amount of water so you probably won’t see much change in the test tube.)

The chemical equations going on during this electrolysis process look like this:

A reduction reaction is happening at the negatively charged cathode. Electrons from the cathode are sticking to the hydrogen cations to form hydrogen gas:

2 H⁺_(aq) + 2e^- --> H_2(g)

2 H₂O_(l) + 2e^- --> H_2(g) + 2 OH^-_(aq)

The oxidation reaction is occurring at the positively charged anode as oxygen is being generated:

2 H₂O_(l) --> O_2(g) + 4 H⁺_(aq) + 4e^-

4 OH^-_(aq) --> O_2(g) + 2 H₂O_(l) + 4 e-

Overall reaction:

2 H₂O_(l) --> 2 H_2(g) + O_2(g)

Note that this reaction creates twice the amount of hydrogen than oxygen molecules. If the temperature and pressure for both are the same, you can expect to get twice the volume of hydrogen to oxygen gas (This relationship between pressure, temperature, and volume is the Ideal Gas Law principle.)

This is the idea behind vehicles that run on sunlight and water. They use a solar panel (instead of a 9V battery) to break apart the hydrogen and oxygen and store them in separate tanks, then run them both back together through a fuel cell, which captures the energy (released when the hydrogen and oxygen recombine into water) and turns the car's motor. Cool, isn't it?

Note: We're going to focus on Alternative Energy in Unit 12 and create all sorts of various energy sources including how to make your own solar battery, heat engine, solar & fuel cell vehicles (as described above), and more!

Exercises

Why are bubbles forming?
Did bubbles form at both wires, or only one? What kind of bubbles are they?
What would happen if you did this experiment with plain water? Would it work? Why or why not?
Which terminal (positive or negative) produced the hydrogen gas?
Did the reaction create more hydrogen or more oxygen?

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Moon Sand

Sunday October 4, 2009

A non-Newtonian fluid is a substance that changes viscosity, such as ketchup. Ever notice how ketchup sticks to the bottom of the bottle one minute and comes sliding out the next?

Think of viscosity as the resistance stuff has to being smeared around. Water is “thin” (low viscosity); honey is “thick” (high viscosity). You are about to make a substance that is both (low and high viscosity), depending on what ratio you mix up. Feel free to mix up a larger batch then indicated in the video – we’ve heard from families that have mixed up an entire kiddie pool of this stuff!

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cornstarch (about 2 cups)
water (about 1 cup)
sand (about 2 cups)

Your first step is to create a 2:1 ratio of cornstarch to water (2 cups cornstarch to 1 cup water). (This is your non-Newtonian fluid.) Grab it with your fist and it will turn rock-solid and crumble; open your hand and it will flow right between your fingers. It’s both a solid and a liquid (it changes viscosity depending on its environment, which is your hand right now). By adding sand to this concoction, you can make moon sand.

Download Student Worksheet & Exercises

Moon sand is basically clay with a beach twist. If you’ve ever tried making a sand castle, you know the disappointment of having the structure crumble after hours of work. Moon sand adds the best properties of clay to the sand for a moldable, sandy texture that’s easy to work with — and it’s dirt cheap to mix up your weight in moon sand.

Your task is to find the perfect ratio of the three ingredients to make this weird substance. If you have too much water, you’ll get a substance that is both a liquid and a solid (as you did before with the non-Newtonian fluid). Too much solid, and it crumbles.

Troubleshooting: The smaller the grain of sand you have, the easier it is to form intricate shapes. If you find white sand, it’ll make better colors when you add food dye to the mixture. Use a large enough bowl and try to keep one hand clean so you can add more (of whatever you need) as you go along. The ideal mixture is approximately 2 cups sand, 2 cups cornstarch, and 1 cup water, give or take a bit. Notice how adding just a small amount of water turns it into a liquid, and adding a tiny bit more cornstarch (or sand) makes it crumble as if it were solid? Take your time to get this mixture just right. (We’ve filled up an entire plastic kiddie pool with this stuff!)
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Microwaving Soap

Friday October 2, 2009

When you warm up leftovers, have you ever wondered why the microwave heats the food and not the plate? (Well, some plates, anyway.) It has to do with the way microwaves work.

Microwaves generate high energy electromagnetic waves that when aimed at water molecules, makes these molecules get super-excited and start bouncing around a lot.

We see this happen when we heat water in a pot on the stove. When you add energy to the pot (by turning on the stove), the water molecules start vibrating and moving around faster and faster the more heat you add. Eventually, when the pot of water boils, the top layer of molecules are so excited they vibrate free and float up as steam.

When you add more energy to the water molecule, either by using your stove top or your nearest microwave, you cause those water molecules to vibrate faster. We detect these faster vibrations by measuring an increase in the temperature of the water molecules (or in the food containing water). Which is why it’s dangerous to heat anything not containing water in your microwave, as there’s nowhere for that energy to go, since the electromagnetic radiation is tuned to excite water molecules.

To explain this to younger kids (who might confuse radio waves with sounds waves) you might try this:

There’s light everywhere, some of which you can see (like rainbows) and others that you can’t see (like the infrared beam coming from your TV remote, or the UV rays from the sun that give you a sunburn). The microwave shoots invisible light beams at your food that are tuned to heat up the water molecule.

The microwave radiation emitted by the microwave oven can also excite other polarized molecules in addition to the water molecule, which is why some plates also get hot. The soap in this experiment below will show you how a bar of Ivory soap contains air, and that air contains water vapor which will get heated by the microwave radiation and expand. Are you ready?

Here’s what you need:

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bar of Ivory soap
microwave (not a new or expensive one)
plate (optional)

The following experiment is a quick example of this principle using a naked bar of Ivory soap. The trick is to use Ivory, which contains an unusually high amount of air. Since air contains water moisture, Ivory also has water hidden inside the bar of soap. The microwave will excite the water molecules and your kids will never look at the soap the same way again.

Download Student Worksheet & Exercises

Toss a naked bar of Ivory soap onto a glass or ceramic plate and stick it into the microwave (don’t use a new or expensive microwave!) on HIGH for 2-3 minutes. Watch intently and remove when it reaches a “maximum”. Be careful when you touch it after taking it out of the microwave oven – it may still hold steam inside. You can still use the soap and the microwave after this experiment!

Note: Scientists refer to ‘light’ as the visible part of the electromagnetic spectrum, where radio and microwaves are lower energy and frequency than light (and the height of the wave can be the size of a football field). Gamma rays and x-rays are higher energy and frequency than light (these tend to pass through mirrors rather than bounce off them. More on that in Unit 9.)

Exercises

What is it in your food (and the soap) that is actually heated by the microwave?
How does a microwave heat things?
Touch the soap after it has been allowed to cool for a few minutes and record your observations.

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Rock Candy Crystals

Friday October 2, 2009

Crystals are formed when atoms line up in patterns and solidify. There are crystals everywhere — in the form of salt, sugar, sand, diamonds, quartz, and many more!

To make crystals, you need to make a very special kind of solution called a supersaturated solid solution. Here’s what that means: if you add salt by the spoonful to a cup of water, you’ll reach a point where the salt doesn’t disappear (dissolve) anymore and forms a lump at the bottom of the glass.

The point at which it begins to form a lump is just past the point of saturation. If you heat up the saltwater, the lump disappears. You can now add more and more salt, until it can’t take any more (you’ll see another lump starting to form at the bottom). This is now a supersaturated solid solution. Mix in a bit of water to make the lump disappear. Your solution is ready for making crystals. But how?

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Here’s what you need:

pencil or wooden skewer
string
glass jar (cleaned out pickle, jam or may jars work great)
8 cups of sugar
3 cups water
paper clip
adult help and a stove
food coloring is optional but fun!

If you add something for the crystals to cling to, like a rock or a stick, crystals can grow. If you “seed” the object (coat it with the stuff you formed the solution with, such as salt or sugar), they will start forming faster. If you have too much salt (or other solid) mixed in, your solution will crystallize all at the same time and you’ll get a huge rock that you can’t pull out of the jar. If you have too little salt, then you’ll wait forever for crystals to grow. Finding the right amount takes time and patience.

Download Student Worksheet & Exercises

1. If you plan on eating the sugar crystal when you’re done you probably want to boil water with the jar and the paper clip in it to get rid of any nasties. Be careful, and don’t touch them while they are hot.

2. Tie one end of the string to the pencil and the opposite end to the paper clip. (You can alternatively use a skewer instead of a piece of string to make it look more like the picture above, but you’ll need to figure out a way to suspend the skewer in the jar without touching the sides or bottom of the jar.)

3. Wet the string a bit and roll it in some sugar. This will help give the sugar crystals a place to start.

4. Place the pencil across the top of the jar. Make sure the clip is at the bottom of the jar and that the string hangs straight down into the jar. Try not to let the sting touch the side of the jar.

5. Heat 3 cups of water to a boil

6. Dissolve 8 cups of sugar in the boiling water (again be careful!). Stir as you add. You should be able to get all the sugar to dissolve. You can add more sugar until you start to see undissolved bits at the bottom of the pan. If this happens, just add a bit of water until they disappear.

7. Feel free to add some food coloring to the water.

8. Pour the sugar water into the jar. Put the whole thing aside in a quiet place for 2 days to a week. You may want to cover the jar with a paper towel to keep dust from getting in.

You should see crystals start to grow in about 2 days. They should get bigger and bigger over the few days. Once you’re happy with how big your crystals get, you can eat them! It’s nothing but sugar! (Be sure to brush your teeth!) This one (left) us about 6 months old.

There you go! Next time you hold a pencil, throw a ball, or put on a shoe try to keep in mind that what you’re doing is using an object that is made of tiny strange atoms all held tightly together by their bonds.

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Penny Crystal Structure

Friday October 2, 2009

The atoms in a solid, as we mentioned before, are usually held close to one another and tightly together. Imagine a bunch of folks all stuck to one another with glue. Each person can wiggle and jiggle but they can’t really move anywhere.

Atoms in a solid are the same way. Each atom can wiggle and jiggle but they are stuck together. In science, we say that the molecules have strong bonds between them. Bonds are a way of describing how atoms and molecules are stuck together.

There’s nothing physical that actually holds them together (like a tiny rope or something). Like the Earth and Moon are stuck together by gravity forces, atoms and molecules are held together by nuclear and electromagnetic forces. Since the atoms and molecules come so close together they will often form crystals.

Try this experiment and then we will talk more about this:
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Here’s what you need:

50 pennies
ruler

Download worksheet and exercises

Lay about 20-50 pennies on the table so that they are all sitting flat on the table. Now, use the ruler (or your hand) to push the pennies toward one another so that you have one big glob of pennies on the table all touching one another. Don’t push so hard that they pile on top of one another. Just get one nice big flat blob of pennies.

Pretty simple huh? However, take a look at the pennies, do you notice anything? You may notice that the pennies form patterns. How could that happen? You just shoved them together you didn’t lay them out in any order. Taa daa! That’s what often happens when solids form.

The molecules are pulled so close to one another that they will form patterns, also known as matrices. These patterns are very dependent on the shape of the molecule so different molecules have a tendency to form different shaped crystals. Salt has a tendency to be “cubey”. Go take a look… and you’ll find that they are like little blocks!

Water has a tendency to from triangle or hexagon shapes which is why snowflakes have six sides. Your pennies also form a hexagon shape. Solids don’t always form crystals but they are more common than you might think. A solid that’s not in a crystalline form is called amorphous. Before you put your pennies away I want you to notice one more thing.

Here’s what you do:

1. Take your pennies and lay them flat on the table.

2. Push them together so they all touch without overlapping.

3. Place your ruler on the right hand side of your penny blob so that it’s touching the bottom half of your pennies.

4. Slowly push the ruler to the left and watch the pennies.

You may have noticed that the penny “crystal” split in quite a straight line. This is called cleavage. Since crystals form patterns the way they do they will tend to break in pretty much the same way you saw your pennies break.

Break an ice cube and take a look. You may see many straight sections. This is because the ice molecules “cleave” according to how they formed. The reason you can write with a pencil is due to this concept. The pencil is formed of graphite crystal. The graphite crystal cleaves fairly easily and allows you to write down your amazing physics discoveries!

(The image here is a graphite crystal.) [/am4show]

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