Solar Drinking Bird

Sunday September 5, 2010


The Drinking Bird is a classic science toy that dips its head up and down into a glass of water. It’s filled with a liquid called methylene chloride, and the head is covered with red felt that gets wet when it drinks. But how does it work? Is it perpetual motion?


Let’s take a look at what’s going on with the bird, why it works, and how we’re going to modify it so it can run on its own without using any water at all!


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The bird needs a temperature difference between the head and tail. Since water needs heat in order to evaporate, the head cools as the water evaporates.  This temperature decrease lowers the pressure inside the head, pushing liquid up the inner tube. With more liquid (weight in the head), the bird tips over. The bird wets its own head to start this cycle again.


The trick to making this work is that when the bird is tipped over, the vapor from the bottom moves up the tube to equalize the pressure in both sides, or he’d stay put with his head in the cup.  Sadly, this isn’t perpetual motion because as soon as you take away the water, the cycle stops. It also stops if you enclose the bird in a jar so water can longer evaporate after awhile. Do you think this bird can work in a rainstorm? In Antarctica?


What’s so special about the liquid? Methylene chloride is made of carbon, hydrogen, and chlorine atoms. It’s barely liquid at room temperature, having a boiling point of 103.5° F, so it evaporates quite easily. It does have a high vapor pressure (6.7 psi), meaning that the molecules on the liquid surface leave (evaporate) and raise the pressure until the amount of molecules evaporating is equal to the amount being shoved back in the liquid (condensed) by its own pressure. (For comparison, water’s vapor pressure is only 0.4 psi).


Note that the vapor pressure will change with temperature changes. The vapor pressure goes up when the temperature goes up. Since the wet head is cooler than the tail, the vapor pressure at the top is less than at the bottom, which pushes the liquid up the tube.


It really does matter whether the bird is operating in Arizona or the Amazon.  The bird will dip more times per minute in a desert than a rain forest!


Let’s find out how to modify the bird so it’s entirely solar-powered… meaning that you don’t have to remember to keep the cup filled with water.  Here’s what you need:


  • drinking bird
  • silver or white spray paint
  • black spray paint
  • razor
  • mug of hot water
  • sunlight or incandescent light


 
Download Student Worksheet & Exercises


In this modification, you completely eliminated the water and converted the bird to solar, using the heat of the sun to power the bird. Now your bird bobs as long as you have sunlight!


How does that work? Since the bottom of the bird is now black, and black absorbs more energy and heats up the tail of the bird. Since the tail section is warmer, the pressure goes up and the liquid gets pushed up the tube. By covering the head with white (or silver) paint, you are reflecting most of the energy so it remains cool. Remember that white surfaces act like mirrors to IR light (which is what heat energy is).


Questions to Ask: Does it work better with hot or cold water? Does it work in an enclosed space, such as an inverted aquarium? On a rainy day or dry? In the fridge or heating pad?


Exercises Answer the questions below:


  1. Where does most of the energy on earth come from?
    1. Underground
    2. The sun
    3. The oceans
  2. What is one way that we use energy from the sun?
  3. What is the process by which the liquid is being heated inside the bird?
    1. Precipitation
    2. Pressure
    3. Evaporation
    4. Transpiration

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Hero Engine

Sunday September 5, 2010

There are lots of different kids of heat engines, from stirling engines to big jet turbines to the engine in your car. They all use clever ways to convert a temperature difference into motion.


Remember that the molecules in steam move around a lot faster than in an ice cube. So when we stick hot steam in a container, we can blow off the lid (used with pistons in a steam engine). or we can put a fan blade in hot steam, and since the molecules move around a lot, they start bouncing off the blade and cause it to rotate (as in a turbine). Or we can seal up hot steam in a container and punch a tiny hole out one end (to get a rocket).


One of the first heat engines was dreamed up by Hero of Alexandria called the aeolipile. The steam is enclosed in a vessel and allowed to jet out two (or more) pipes. Although we’re not sure if his invention ever made it off the drawing board, we do know how to make one for pure educational (and entertainment) purposes.  Are you ready to have fun?


THIS EXPERIMENT USES FIRE AND STEAM…GET ADULT HELP BEFORE YOU OPERATE THE ENGINE.

Here’s what you do:


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Materials:


  • soda can
  • fishing line
  • razor
  • stand
  • drill or large nail and hammer
  • adult help
  • candle


IMPORTANT NOTE: As the water boils, your can will spin. The hot steam shoots out the sides, so take care not to get burned. As the can spins, it may wobble and shake, especially if it’s off-center.  Be careful not to get shot with boiling water!!


What’s going on? When the water boils, the molecules inside are turning into hot steam and moving very quickly, bouncing off the can and out the pipes. Rockets and balloons use this same principle – the pressurized air shoots out the open end and the balloon (or rocket)  moves in the opposite direct.  Newton’s third law in motion! The two jets at an angle work together to spin the can.


  1. Do you think the size of the hole matters?
  2. Does it matter how many candles you use?
  3. What if you used four holes instead of two? Six? Twenty?
  4. Are beer cans better?

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Food Dye Currents

Sunday September 5, 2010

When something feels hot to you, the molecules in that something are moving very fast. When something feels cool to you, the molecules in that object aren’t moving quite so fast. Believe it or not, your body perceives how fast molecules are moving by how hot or cold something feels. Your body has a variety of antennae to detect energy. Your eyes perceive certain frequencies of electromagnetic waves as light. Your ears perceive certain frequencies of longitudinal waves as sound. Your skin, mouth and tongue can perceive thermal energy as hot or cold. What a magnificent energy sensing instrument you are!


Let’s find out how to watch the hot and cold currents in water. Here’s what you need to do:


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Materials:


  • two bottles of water
  • food coloring
  • bathtub or sink
  • index card or business card


 
You need:


Two empty bowls (or water bottles)
Food coloring
Hot water (Does not need to be boiling.)
Cold water


1. Put about the same amount of water into two bowls. One bowl should be filled with hot water from the tap. If you’re careful, you can put it in the microwave to heat it up but please don’t hurt yourself. The other bowl should have cold water in it. If you’re using water bottles, pour the hot and cold water into each bottle.


2. Let both bowls sit for a little bit (a minute or so) so that the water can come to rest.


3. Put food coloring in both bowls (or bottles) and watch carefully.


The food coloring should have spread around faster in the hot water bowl than in the cold water bowl. Can you see why? Remember that both bowls are filled with millions and millions of molecules. The food coloring is also bunches of molecules. Imagine that the molecules from the water and the molecules from the food coloring are crashing into one another like the beans on the plate. If one bowl has a higher temperature than the other, does one bowl have faster moving molecules? Yes, the higher temperature means a higher thermal energy. So the bowl with the warmer water has faster moving molecules which crash more and harder with the food coloring molecules, spreading them faster around the bowl.


If you’re using a bottle, you can do an extra step: For bottles, place a business card over the cold bottle and invert the cold bottle over the hot. Remove card.


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Making Clouds

Sunday September 5, 2010

Indoor Rain Clouds

Making indoor rain clouds demonstrates the idea of temperature, the measure of how hot or cold something is. Here’s how to do it:


Take two clear glasses that fit snugly together when stacked. (Cylindrical glasses with straight sides work well.)


Fill one glass half-full with ice water and the other half-full with very hot water (definitely an adult job – and take care not to shatter the glass with the hot water!). Be sure to leave enough air space for the clouds to form in the hot glass.


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Place the cold glass directly on top of the hot glass and wait several minutes. If the seal holds between the glasses, a rain cloud will form just below the bottom of the cold glass, and it actually rains inside the glass! (You can use a damp towel around the rim to help make a better seal if needed.)


Materials:


  • glass of ice water
  • glass of hot water (see video)
  • towel
  • adult help


  Download Student Worksheet & Exercises


Bottling Clouds

On a stormy, rainy afternoon, try bottling clouds — using the refrigerator! Here’s what you do: Place an empty, clean 2-liter soda bottle in the fridge overnight. Take it out and get an adult to light a match, letting it burn for a few seconds, then drop it into the bottle. Immediately cap the bottle and watch what happens (you should see smoke first, then clouds forming inside). Squeeze the sides of the bottle. The clouds should disappear. When you release the bottle, the clouds should reappear. Materials:


  • 2L soda bottle
  • rubbing alcohol
  • bicycle pump
  • car tire valve (drill a 1/2 inch hole through a 2L soda bottle cap and pull the valve gently through with pliers)


Advanced Idea: You can substitute rubbing alcohol and a bicycle pump for the matches to make a more solid-looking cloud.  Swirl a bit of rubbing alcohol around inside the bottle, just enough to coat the insides, and then pour it out.  Cap your bottle with a rubber stopper fitted with a needle valve (so the valve is poking out of the bottle), and apply your pump.  Increase the pressure inside the bottle (keep a firm hand on the stopper or you’ll wind up firing it at someone) with a few strokes and pull out the stopper quickly.  You should see a cloud form inside.


What’s going on? Invisible water vapor is all around us, all the time, but they normally don’t stick together. When you squeezed the sides of the bottle, you increased the pressure and squeezed the molecules  together.  Releasing the bottle decreases the pressure, which causes the temperature to drop. When it cools inside, the water molecules stick to the smoke molecules, making a visible cloud inside your bottle.


Did you know that most drops of water actually form around a dust particle?  Up in the sky, clouds come together when water vapor condenses into liquid water drops or ice crystals. The clouds form when warm air rises and the pressure is reduced (as you go up in altitude). The clouds form at the spot where the temperature drops below the dew point.


The alcohol works better than the water because it evaporates faster than water does, which means it moves from liquid to vapor more easily (and vividly) than regular old water.


Questions to ask:


  • How many times can you repeat this?
  • Does it matter what size the bottle is?
  • What if you don’t chill the bottle?
  • What if you freeze the bottle instead?

Exercises


  1. Which combination made it rain the best? Why did this work?
  2. Draw your experimental diagram, labeling the different components:
  3. Add in labels for the different phases of matter. Can you identify all three states of matter in your experiment?

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Peanut Energy

Sunday September 5, 2010

This experiment is for advanced students. Did you know that eating a single peanut will power your brain for 30 minutes? The energy in a peanut also produces a large amount of energy when burned in a flame, which can be used to boil water and measure energy.


Peanuts are part of the bean family, and actually grows underground (not from trees like almonds or walnuts).  In addition to your lunchtime sandwich, peanuts are also used in woman’s cosmetics, certain plastics, paint dyes, and also when making nitroglycerin.


What makes up a peanut?  Inside you’ll find a lot of fats (most of them unsaturated) and  antioxidants (as much as found in berries).  And more than half of all the peanuts Americans eat are produced in Alabama. We’re going to learn how to release the energy inside a peanut and how to measure it.


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Materials:


  • raw peanuts
  • chemistry stand with glass test tube and holder (watch video)
  • flameproof surface (large ceramic tile or cookie sheet)
  • paper clip
  • alcohol burner or candle with adult help
  • fire extinguisher


Download Student Worksheet & Exercises


What’s Going On? There’s chemical energy stored inside a peanut, which gets transformed into heat energy when you ignite it. This heat flows to raise the water temperature, which you can measure with a thermometer.  You should find that your peanut contains 1500-2100 calories of energy!  Now don’t panic…  this isn’t the same as the number of calories you’re allowed to eat in a day.  The average person aims to eat around 2,000 Calories (with a capital “C”).  1 Calorie = 1,000 calories.  So each peanut contains 1.5-2.1 Calories of energy (the kind you eat in a day). Do you see the difference?


But wait… did all the energy from the peanut go straight to the water, or did it leak somewhere else, too?  The heat actually warmed up the nearby air, too, but we weren’t able to measure that. If you were a food scientist, you’d use a nifty little device known as a bomb calorimeter to measure calorie content.  It’s basically a well-insulated, well-sealed device that catches nearly all the energy and flows it to the water, so you get a much more accurate temperature reading. (Using a bomb calorimeter, you’d get 6.1-6.8 Calories of energy from one peanut!)


How do you calculate the calories from a peanut?

Let’s take an example measurement.  Suppose you measured a temperature increase from 20 °C to 100 °C for 10 grams of water, and boiled off 2 grams.  We need to break this problem down into two parts – the first part deals with the temperature increase, and the second deals with the water escaping as vapor.


The first basic heat equation is this:


Q = m c T


Q is the heat flow (in calories)
m is the mass of the water (in grams)
c is the specific heat of water (which is 1 degree per calorie per gram)
and T is the temperature change (in degrees)


So our equation becomes: Q = 10 * 1 * 80 = 800 calories.


If you measured that we boiled off 2 grams of water, your equation would look like this for heat energy:


Q = L m


L is the latent heat of vaporization of water (L= 540 calories per gram)
m is the mass of the water (in grams)


So our equation becomes: Q = 540 * 2 = 1080 calories.


The total energy needed is the sum of these two:


Q = 800 calories + 1080 calories = 1880 calories.


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Boiling Room Temperature Water

Sunday September 5, 2010

The triple point is where a molecule can be in all three states of matter at the exact same time, all in equilibrium. Imagine having a glass of liquid water happily together with both ice cubes and steam bubbles inside, forever! The ice would never melt, the liquid water would remain the same temperature, and the steam would bubble up. In order to do this, you have to get the pressure and temperature just right, and it’s different for every molecule.


The triple point of mercury happens at -38oF and 0.000000029 psi. For carbon dioxide, it’s 75psi and -70oF. So this isn’t something you can do with a modified bike pump and a refrigerator.


However, the triple point of water is 32oF and 0.089psi. The only place we’ve found this happening naturally (without any lab equipment) is on the surface of Mars.


Because of these numbers, we can get water to boil here on Earth while it stays at room temperature by changing the pressure using everyday materials. (If you have a vacuum pump, you can have the water boil at the freezing point of 32oF.)


Here’s what you need to do:


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Materials:


  • plastic syringe (no needle)
  • room temperature water


Bonus Idea: Do this experiment first with water, then with carbonated water.


Why does that work? How did you get the pressure to decrease? Easy – when you pulled on the plunger and increased the volume inside the syringe. Since your finger covered the hole, no additional air was allowed in when you did this (which is why it was probably a little tough to do), so the number of molecules inside the syringe stayed the same, but the space they had to wiggle around got a lot bigger, meaning that the pressure decreased.


The air inside the syringe isn’t just plain old air… it has water vapor inside, too. And that’s not all – the water from your sink isn’t just plain old water, it has air bubbles mixed in with it. When you brought down the pressure (by pulling the plunger), you are forcing the air bubbles to come out of the water, which makes it boil. When you shove the plunger back in and increase the pressure, you’ll find that the air bubbles mix back into the water and disappears.


Did you try the soda water yet? Soda has carbon dioxide already mixed in for you, which is under pressure. You can release this pressure by opening the bottle (you’ll hear a PSSST!), which is the carbon dioxide bubbles coming out of the soda. Go ahead and try that now before reading further…


When you place the soda water into the syringe and decrease the pressure, the carbon dioxide comes out quickly Try tapping the syringe to make all the tiny bubbles combine into one larger bubble. When you increase the pressure (push the plunger back in), some of the bubbles will redissolve back into the soda.


If you’ve ever had a glass of hot water suddenly erupt in an explosion of bubbles, you’ve experienced superheated water (water that’s above it’s normal boiling point) that hasn’t been able to form bubbles yet. By adding a tea bag or simply just jiggling it around is usually enough to cause the bubbles to start, which often splatters HOT HOT water everywhere. (This isn’t something you want to try without adult help.)


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Stairstep Candles

Sunday September 5, 2010

Fire is a chemical reaction (combustion) involving hot gases and plasma. The three things you need for a flame are oxygen, fuel, and a spark. When the fuel (gaseous wax) and oxygen (from the air) combine in a flame, one of the gases produced is carbon dioxide.


Most people think of carbon dioxide as dry ice, and are fascinated to watch the solid chunk sublimate from solid straight to gas, skipping the liquid state altogether. You’ve seen the curls of dry ice vapor curl down and cover the floor in a thick, wispy fog. Is carbon dioxide always more dense than air, or can we get it to float?


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The answer is… yes! Here’s an experiment that will walk you through how to create a hot, invisible cloud of carbon dioxide and detect where that cloud is.


Materials:


  • three candles
  • adult help
  • blocks or stones
  • LARGE jar that fits over all three candles (watch video)


Download Student Worksheet & Exercises


Carbon dioxide changes volume when you heat or cool it. When you heat the CO2, the volume expands, lowering the density to less than that of air. When the CO2 cools, the cloud contracts (gets smaller), and the density increases as it falls to the floor.


Remember density is mass per unit volume. So it’s an inverse relationship – when volume goes up, density goes down. In this experiment, when the temperature goes up, the volume goes up, and the density goes down.
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Soaking Up Rays

Sunday September 5, 2010

Heat is transferred by radiation through electromagnetic waves. Remember, when we talked about waves and energy? Well, heat can be transferred by electromagnetic waves. Energy is vibrating particles that can move by waves over distances right? Well, if those vibrating particles hit something and cause those particles to vibrate (causing them to move faster/increasing their temperature) then heat is being transferred by waves. The type of electromagnetic waves that transfer heat are infra-red waves. The Sun transfers heat to the Earth through radiation.


If you hold your hand near (not touching) an incandescent light bulb until you can feel heat on your hand, you’ll be able to understand how light can travel like a wave. This type of heat transfer is called radiation.


Now don’t panic. This is not a bad kind of radiation like you get from x-rays. It’s infra-red radiation. Heat was transferred from the light bulb to your hand. The energy from the light bulb resonated the molecules in your hand. (Remember resonance?) Since the molecules in your hand are now moving faster, they have increased in temperature. Heat has been transferred! In fact, an incandescent light bulb gives off more energy in heat then it does in light. They are not very energy efficient.


Now, if it’s a hot sunny day outside, are you better off wearing a black or white shirt if you want to stay cool? This experiment will help you figure this out:


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You need:


  • 2 ice cubes, about the same size.
  • A white piece of paper
  • A black piece of paper
  • A sunny day


 


Download Student Worksheet & Exercises


1. Put the two pieces of paper on a sunny part of the sidewalk.


2. Put the ice cubes in the middle of the pieces of paper.


3. Wait.


What you should eventually see, is that the ice cube on the black sheet of paper melts faster then the ice cube on the white sheet. Dark colors absorb more infra-red radiation then light colors. Heat is transferred by radiation easier to something dark colored then it is to something light colored and so the black paper increased in temperature more then the white paper.


So, to answer the shirt question, a white shirt reflects more infra-red radiation so you’ll stay cooler. White walls, white cars, white seats, white shorts, white houses, etc. all act like mirrors for infra-red (IR) radiation. Which is why you can aim your TV remote at a white wall and still turn on the TV. Simply pretend the wall is a mirror (so you can get the angle right) and bounce the beam off the wall before it gets to your TV. It looks like magic!


Click over to this experiment to learn how to make Liquid Crystals.


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Liquid Crystals

Sunday September 5, 2010

If you’ve completed the Soaking Up Rays experiment, you might still be a bit baffled as to why there’s a difference between black and white. Here’s a great way to actually “see” radiation by using liquid crystal thermal sheets.


You’ll need to find a liquid crystal sheet that has a temperature range near body temperature (so it changes color when you warm it with your hands.)


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The liquid crystal sheet is temperature-sensitive. When the sheet received heat from the bulb, the temperature goes up and changes color. The plastic sheets remain black except for the temperature range in which they display a series of colors that reflect the actual temperature of the crystal.


Materials:



1. Color half of the back side of the thermal paper (the side that doesn’t change color) with the highlighter (or cover half of it with foil).


2. Hold it in a position where you can easily see the color-changing side while keeping the light source on the back side.


3. Which side changes color? Is there a difference between the silver and black halves?


You’ll notice that the black half almost immediately changes color, while the silver side stays black.  The silver coating reflects the heat, keeping it cool. The black side absorbs the heat and raises its temperature.


Why do liquid crystals change color with temperature? Your liquid crystal sheet is not just one sheet, but a stack of several sheets that are slightly offset from each other. The distance between each layer changes as the sheet warms up – the hotter the temperature, the closer the stacks twist together. The color they emit depends on the distance between the sheets.


The molecules that make up the sheets are long and thin, like hot dogs. When the sheets are cooler, these molecules move around less and don’t twist up as much, which corresponds to reflecting back a redder light.  When the temperature rises, the molecules move around more and twist together, and they reflect a bluer light. When the liquid crystal sheet is black, all the light is absorbed (no light gets reflected).


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Simple Microscope & Telescope

Wednesday September 1, 2010

Did you know you can create a compound microscope and a refractor telescope using the same materials? It’s all in how you use them to bend the light. These two experiments cover the fundamental basics of how two double-convex lenses can be used to make objects appear larger when right up close or farther away.


Things like lenses and mirrors can bend and bounce light to make interesting things, like compound microscopes and reflector telescopes. Telescopes magnify the appearance of some distant objects in the sky, including the moon and the planets. The number of stars that can be seen through telescopes is dramatically greater than can be seen by the unaided eye.


Materials


  • A window
  • Dollar bill
  • Penny
  • Two hand-held magnifying lenses
  • Ruler

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Download Student Worksheet & Exercises


  1. Place a penny on the table.
  2. Hold one magnifier above the penny and look through it.
  3. Bring the second magnifying lens above the first so now you’re looking through both. Move the second lens closer and/or further from the penny until the penny comes into sharp focus. You’ve just made a compound microscope.
  4. Who’s inside the building on an older penny?
  5. Try finding the spider/owl on the dollar bill. (Hint: It’s in a corner next to the “1”.)
  6. Keeping the distance between the magnifiers about the same, slowly lift up the magnifiers until you’re now looking through both to a window.
  7. Adjust the distance until your image comes into sharp (and upside-down) focus. You’ve just made a refractor telescope, just like Galileo used 400 years ago.
  8. Find eight different items to look at through your magnifiers. Make four of them up-close so you use the magnifiers as a microscope, and four of them far-away objects so you use the magnifiers like a telescope. Complete the data table.

What’s Going On?

What I like best about this activity is how easily we can break down the basic ideas of something that seems much more complex and intimidating, like a telescope or microscope, in a way that kids really understand.


When a beam of light hits a different substance (like a window pane or a lens), the speed at which the light travels changes. (Sound waves do this, too!) In some cases, this change 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 (186,282 miles per second). This is 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. 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?


Why does the pencil appear bent? Is it always bent? Does the temperature of the water affect how bent the pencil looks? What if you put two pencils in there?


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.


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


Exercises


  1. Can light change speeds?
  2. Can you see ALL light with your eyes?
  3. Give three examples of a light source.
  4. What’s the difference between a microscope and a telescope?
  5. Why is the telescope image upside-down?

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Microwhat?

Saturday July 31, 2010

Welcome to our unit on microscopes! We’re going to learn how to use our microscope to make things appear larger so we can study them more easily. Think about all the things that are too small to study just with your naked eyeballs: how many can you name?


Let’s start from the inside out – before you haul out your own microscope, we’re going to have a look at what it can do. I’ve already prepared a set of slides for you below.  Take out a sheet of paper and jot down your guesses – here’s how you do it:


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What is it?

Take a peek and see if you can figure out what each one is. Record your guess on a piece of paper. Don’t spend more than 90 seconds on each one. If you’re working with others, have everyone write down their answers individually, and then work together and discuss each one. Come up with a final group conclusion what’s on each slide before peeking at the answers.


plant cells
Paramecium Respiratory Tissue Hair Follicle
Green Algae Water Flea Pine Wood

Need answers? Hover your mouse over each slide to reveal the title.


More questions you can ask:

1. List the ways that microscopes are used. Why bother using them anyway? (Can you name four?)


2. What do you already know about microscopes? List two things.


3. What would you really like to learn about microscopes? Name three, at least.


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Anatomy of the Microscope

Saturday July 31, 2010

Nose? Objective? Stage? What kind of class is this?  Well, some of the names may sound a bit odd, but this video will show you what they are and how they are used. As you watch the video, touch the corresponding part of your microscope to get a feel for how it works.


NOTE: Be very careful NOT to raise the stage too high or you’ll crack the objective lens!  Always leave a space between the stage and the lens!! Anytime you use the coarse adjustment knob, always look at the stage itself, NOT through the eyepiece (for this very reason). When you use the fine adjustment knob, that’s when you look through the eyepiece.




More questions to ask:

1. After you’ve learned the different parts of the microscope, swing around and teach it to a nearby grown-up to test your knowledge. See if you can find all these parts: eyepiece, base (legs), objective lens, eyepiece, diaphragm (or iris), stage, fine and coarse adjustment knobs, mirror/lamp, nose.


2. Show your grown-up which parts never to touch with your fingers.


3. What’s the proper way to use the coarse adjustment knob so you don’t crack the objective lens?


Care and Cleaning

1. Pick up the microscope with two hands. Always grab the arm with one hand and the legs (base) with the other.


2. Don’t touch the lenses with your fingers. The oil on your fingers will smudge and etch the lenses. Use an optical wipe if you must clean the lenses. Steer clear of toilet paper and paper towels – they will scratch your lenses.


3. When you’re done with your scope for the day, reset it so that it’s on the lowest power of magnification and lower the stage to the lowest position. Cover it with your dust cover or place it in its case.


How to Use a Microscope: Optics, Observing, and Drawing Techniques

Saturday July 31, 2010

How do the lenses work to make objects larger? We’re going to take a closer look at optics, magnification, lenses, and how to draw what you see with this lesson. Here’s a video to get you started:




Here’s what you do:


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1. Take a look at the eyepiece of your microscope. Do you see a number followed by an X? That tells you the magnification of your microscope. If it’s a 10X, then it will make objects appear ten times larger than usual.


2. Peek at the objective lenses. They’re on the nose of the microscope, and there’s usually 3 or 4 of them. Do you see the little numbers printed on the side of the lenses, also followed by an X? Find the one that says 4. if you look through just that lens by itself, objects will appear 4 times as large. However, it’s in a microscope, so you’re actually looking through two lenses when you use the microscope. What that means is that you need to multiply this number by the eyepiece magnification (in our example, it’s 4 * 10 = 40) to get the total power of magnification when you use the microscope on this power setting. It’s 40X when you use the 10X eyepiece and 4X objective. So objects are going to appear 40 times larger than in real life.


3. Practice these with your microscope – here are the settings on my microscope – help me fill out the table to figure out how to set the lenses for the different magnification powers:


Eyepiece
Objective
Total Magnification
10X
4X
10X
100X
40X
400X
10X
1000X



Questions to Ask:

1. What does this table above look like for your microscope?


2. Your microscope may have come with an additional eyepiece. If so, add it to your table and figure out the range of magnification you have.


3. What is your highest power of magnification? Set it now.


4. List three possible combination of eyepiece and objective lenses if the power of magnification is 100X.


Learning to Look

Do how do you use this microscope thing, anyway? Here’s how you prepare, look, and adjust so you can get a great view of the micro world:




Download Student Worksheet & Exercises


1. Carefully cut a single letter (like an “a” or “e”) from a printed piece of paper (newspaper works well).


2. Use your tweezers to place the small letter on a slide and place a coverslip over it (be careful with these – they are thin pieces of glass that break easily!) If your letter slides around, add a drop of water and it should stick to the slide.


3. Lower the stage to the lowest setting using the coarse adjustment knob (look at the stage when you do this, not through the eyepiece).


4. Place your slide in the stage clips.


5. Turn the diaphragm to the largest hole setting (open the iris all the way).


6. Move the nose so that the lowest power objective lens is the one you’re using.


7. Bring the stage up halfway and peek through the eyepiece.


8. If you’re using a mirror, rotate the mirror as you look through the eyepiece until you find the brightest spot. You’ll probably only see a fuzzy patch, but you should be able to tell bright from dim at this point.


9. Use the coarse adjust to move the stage slowly up to bring it into rough focus. If you’ve lowered the stage all the way in step 7, you’ll see it pop into focus easily. (Be careful you don’t ram the stage into the lens!)


10. Use the fine adjust to bring it into sharp focus. What do you see?


Drawing What You See

Learning to sketch what you see is important so that the view is useful to more than just you. Here’s the easy way to do it: get a water glass and trace around the rim on a sheet of paper with your pencil. This gives you a nice, large circle that represents your scope’s field of view (what you see when you look into the microscope). Now you’re ready for the next step:




1. Draw a picture of that the letter looks like under the lowest power setting in your first circle and label it ‘right side up’. Then give the slide a half turn and draw another picture in a new circle. Label this one ‘upside-down’.


2. If you’re using a mechanical stage (which we highly recommend), twist one of the knobs so that the slide physically moves to the right as you look from the side (not through the eyepiece) of the microscope. If you’re using stage clips, just nudge the slide to the right with your finger. Now peek through the eyepiece as you move the slide to the right – which way does your letter move?


3. Now do the same for the other direction – make the slide move toward you. Which way does the letter appear to move when you look through the eyepiece?


4. What effect do the two lenses have on the letter image as you move it around? (Need a hint? Look back at the Microscope Optics Lesson from Unit 9)


Look back at your two drawings above. Let’s make them so they are totally useful, the way scientists label their own sketches. We’re going to add a border, title, power of magnification, and more to get you in the habit of labeling correctly. Here’s how you do it:


Border You need to frame the picture so the person looking at it knows where the image starts and ends. Use a water glass to help make a perfect circle every time. When I sketch at the scope, I’ll fill an entire page with circles before I start so I can quickly move from image to image as I switch slides.


Title What IS it? Paramecia, goat boogers, or just a dirty slide? Let everyone (including you!) know what it is by writing exactly what it is. You can use bold lettering or underline to keep it separate from any notes you take nearby.


Magnification Power This is particularly useful for later, if you need to come back and reference the image. You’ll be quickly and easily able to duplicate your own experiment again and again, because you know how it was done.


Proportions This is where you need to draw only what you see. Don’t make the image larger or smaller – just draw exactly what you see. If it’s got three legs and is squished in the upper right corner, then draw that. Most people draw their image smaller than it really is when viewed through the eyepiece. If it helps, mentally divide the circle into four quarters and look at each quarter-circle and make it as close to what you see as you can.


Exercises


  1. Why do we use microscopes?
  2. What’s the highest power of magnification on your microscope? Lowest?
  3. Where are the two places you should NEVER touch on your microscope?
  4. Fill in the blanks with the appropriate word to describe care and cleaning of your microscope:fingers       lowest                                               handsarm                                       toilet paper                                    legs                        dust cover
    1. Pick up the microscope with two ________.  Always grab the _________with one hand and the _______(base) with the other.
    3. Don’t touch the lenses with your _________. The oil will smudge and etch the lenses. Use an optical wipe if you must clean the lenses. Steer clear of ____________ and paper towels – they will scratch your lenses.
    5. When you’re done with your scope for the day, reset it so that it’s on the _________ power of magnification and lower the stage to the lowest position. Cover it with your __________ or place it in its case.
  5.  What things must be present on your drawing so others know what they’re looking at?
  6.  What’s the proper way to use the coarse adjustment knob so you don’t crack the objective lens?
  7.   List three possible combination of eyepiece and objective lenses if the power of magnification is 100X.
  8.  Briefly describe how to dry mount a slide.
  9.  How could you view a copper penny with your microscope?

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Preparing a Dry Mount Slide

Saturday July 31, 2010

Make sure you’ve completed the How to Use a Microscope activity before you start here!


This is simplest form of slide preparation!  All  you need to do is place it on the slide, use a coverslip (and you don’t even have to do that if it’s too bumpy), and take a look through the eyepiece.  No water, stains, or glue required.


You know that this is the mount type you need when your specimen doesn’t require water to live. Good examples of things you can try are cloth fibers (the image here is of cotton thread at 40X magnification), wool, human hair, salt, and sugar. It’s especially fun to mix up salt and sugar first, and then look at it under the scope to see if you can tell the difference.


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Here’s what you do:



1. Pull a hair from your head and lay it on a slide. If it’s super-curly, use a bit of tape at either end, stretching it along the length of the slide. Keep the tape near the ends so it doesn’t come into your field of view when you look through the microscope.


2. Lower the stage to the lowest setting and rotate the nose piece to the lowest magnification power.


3. Place the slide on the stage in your clips.


4. Focus the hair by looking through the eyepiece and slowly turning the coarse adjustment knob. When you’re close to focus, switch to the fine adjustment knob until it pops into sharp view.


5. Open your science notebook and draw a circle. Sketch what you see (don’t forget the title and mag power!)


6. When you’re done, lower the stage all the way and insert a new slide… and repeat. Find at least six things to look at. We’re not only learning how to look and draw, but hammering a habit of how to handle the scope properly, so do as many as you can find.


Don’t forget to check the windowsills for interesting bits. Use baby food jars or film canisters to collect your specimens in and keep them safe until you need them.


TIP: If you want to keep your specimen on the slide for a couple of months, use a drop of super glue and lay a coverslip down on top, pressing gently using a toothpick (not your fingers) to get the air bubbles out. Let dry.


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Preparing a Wet Mount Slide

Saturday July 31, 2010

Make sure you’ve completed the How to Use a Microscope activity before you start here!


Anytime you have a specimen that needs water to live, you’ll need to prepare a wet mount slide. This is especially useful for looking at pond water (or scum), plants, protists (single-cell animals), mold, etc. When you keep your specimen alive in their environment, you not only get to observe it, but also how it eats, lives, breathes, and interacts in its environment.


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The first thing you need to do is collect your pond water. Make sure it has lots of good stuff in it! You’ll need a 20mL sample. Once you have it, place it on a table along with your microscope, slides, cover slips, tweezers, and dropper. If you’re using Protoslo (if critters are too fast, this slow them down for easier viewing), get that out, too. Open up your science notebook, draw a bunch of circles for drawing borders, and then watch this video:



Download Student Worksheet & Exercises


1. Place a slide on the table.


2. Fill the eyedropper with pond water and place a drop on the slide.


3. Place the edge of the cover slip on the pond water drop, holding the other edge up at an angle. Slowly lower the end down so that the drop spreads out. You want a very thin film to lay on the slide without any air bubbles or excess water squirting out. If you go have bubbles, gently press down on the cover slip to squish them out or start over.


4. Take time practicing this – you want the water only under the coverslip. Dab away excess water that’s not under the slide with a paper towel.


5. Lower the stage to the lowest setting and rotate the nose piece to the lowest magnification power.


6. Place the slide on the stage in your clips.


7. Focus by looking through the eyepiece and slowly turning the coarse adjustment knob. When you’re close to focus, switch to the fine adjustment knob until it pops into sharp view.


8. Adjust the light level to get the greatest contrast so you can see better.


9. Move the slide around (this is where a mechanical stage is wonderful to have) until you spot something interesting. Place it in the center of your field of view, and switch magnification power to find a great view (not too close, not to far away). Adjust your focus as needed.


8. Open your science notebook and draw a circle. Sketch what you see (don’t forget the title and mag power!)


9. When you’re done, lower the stage all the way and insert a new slide… and repeat. Find at least six things to look at. We’re not only learning how to look and draw, but hammering a habit of how to handle the scope properly, so do as many as you can find.


NOTE: If the critters you’re looking at move too fast, add a drop of Protoslo to the edge of your slide to slow them down (by numbing them). The Protoslo will work its way under the cover slip.


Exercises


  1. Why do we use a wet mount slide?
  2. Give one example of a specimen that would use a wet mount slide?
  3. How do you prepare a wet mount slide?
  4. Why do we stain specimens?
  5. Give one example of a specimen that would use a stain.
  6. What type of stain can we use (give at least one example).

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Slide Preparation: Staining

Saturday July 31, 2010

Make sure you’ve completed the How to Use a Microscope and also the Wet Mount activities before you start here!


If your critter is hard to see, you can use a dye to bring out the cell structure and make it easier to view.  There are lots of different types of stains, depending on what you’re looking at.


The procedure is simple, although kids will probably stain not only their specimens, but the table and their fingers, too.  Protect your surfaces with a plastic tablecloth and use gloves if you want to.


We’re going to use an iodine stain, which is used in chemistry as an indicator (it turns dark blue) for starch. This makes iodine a good choice when looking at plants. You can also use Lugol’s Stain, which also reacts with starch and will turn your specimen black to make the cell nuclei visible. Methylene blue is a good choice for looking at animal cells, blood, and tissues.


In addition to your specimen, you’ll need to get out your slides, microscope, cover slips, eye dropper, tweezers, iodine (you can use regular, non-clear iodine from the drug store), and a scrap of onion. If you can find an elodea leaf, add it to your pile (check with your local garden store). Here’s what you do:


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Download Student Worksheet & Exercises


1. Fill a container with water and add a small piece of elodea leaf and onion. You’ll want the onion to be a thin slice, no more than a quarter of an inch thick.


2. Practice making a wet mount first.  Put a fresh slide on the table. Using tweezers, pull off a thin layer of onion (use a layer from the middle, not the top) and place it on your slide. Gently stretch out the wrinkles (use a toothpick or tweezers) and add a small drop of water and cover with a cover slip. Take a peek at what your specimen looks like on low power – do  you notice it’s hard to see much?  Draw what you see in your notebook.


3. Now increase the power and look again.  Draw a new sketch in your notebook.


4. Now we’re going to highlight the cell structure using iodine.  Lugol’s is also iodine, but the regular brown stuff from the drug store works, too. Grab a bottle of the one you’re going to use.


5. To stain the specimen, we’re going to add the stain to one side of the cover slip and wick away the water from the other side. Use a folded piece of tissue paper and touch it lightly to one side of the cover slip as you add a single drop of stain to the other side. When the stain has flowed through the entire specimen, take a peek and draw what you see in a a fresh circle.


6. Do the same thing with the elodea leaf. And anything else plant-based from your backyard. Or refrigerator.  Draw what you see and don’t forget to label it with a title and power of magnification!


Exercises


  1. Why do we use a wet mount slide?
  2. Give one example of a specimen that would use a wet mount slide?
  3. How do you prepare a wet mount slide?
  4. Why do we stain specimens?
  5. Give one example of a specimen that would use a stain.
  6. What type of stain can we use (give at least one example).

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Slide Preparation: Heat Fixes

Saturday July 31, 2010

Make sure you’ve completed the How to Use a Microscope and also the Wet Mount and Staining activities before you start here!


If you tried looking at animal cells already, you know that they wiggle and squirm all over the place. And if you tried looking when using the staining technique, you know it only makes things worse.


The heat fix technique is the one you want to use to nail your specimen to the slide and also stain it to bring out the cell structure and nuclei. This is the way scientists can look at things like bacteria.


You’re going to need your microscope, slides, cover slips, eyedropper, toothpicks or tweezers, candle and matches (with adult help), stain (you can use regular iodine or Lugol’s Stain), sugar, yeast, and a container to mix your specimen in. Here’s what you do:


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Download Student Worksheet & Exercises


1. Fill your container with warm water.  Add about a tablespoon of yeast (one packet is enough) along with a teaspoon of sugar.  The warm water activates the yeast and the sugar feeds it.  You should see a foam top form in about 10 minutes.


2. Using your eyedropper, grab a bit of your sample (you want the liquid, not the foam) and place a drop on a fresh slide. Spread the drop out with a toothpick.  You want to smear it into a thin layer.


3. Light the candle (with adult help). Heat the slide in the flame by gently waving it back and forth. Don’t stop it in the flame, or you’ll get black soot on the underside of the slide and possibly crack it because the glass heats up and expands too fast. You also don’t want to cook the yeast, as it will destroy what you want to look at. Just wave it around to evaporate the water.


4. Add a drop of iodine (or stain) to the slide. Wait 15 seconds.


5. Rinse it under water. (You can optionally stain it again if you find it’s particularly difficult to see your specimen, but make sure to look at it first before repeat staining.)


6. Place a drop of water (use a clean eyedropper) on the specimen and add the cover slip.


7. Lower the stage to the lowest setting and rotate the nose piece to the lowest magnification power.


8. Place the slide on the stage in your clips.


9. Focus by looking through the eyepiece and slowly turning the coarse adjustment knob. When you’re close to focus, switch to the fine adjustment knob until it pops into sharp view.


10. Adjust the light level to get the greatest contrast so you can see better.


11. Move the slide around (this is where a mechanical stage is wonderful to have) until you spot something interesting. Place it in the center of your field of view, and switch magnification power to find a great view (not too close, not to far away). Adjust your focus as needed.


12. Open your science notebook and draw a circle. Sketch what you see (don’t forget the title and mag power!)


NOTE: What other things can you look at?  You can scrape the inside of your cheek with a toothpick and smear it on a fresh slide, take a mold sample from last week’s leftovers in the fridge, or…? Have fun!


Exercises


  1. Why do we use heat fixes?
  2. Briefly describe how to do a heat fix.
  3. What is a specimen that needs a heat fix?

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PVA Slime

Wednesday June 30, 2010

Instead of using glue as a polymer (as in the slime recipes above), we're going to use PVA (polyvinyl alcohol). Most liquids are unconnected molecules bouncing around. Monomers (single molecules) flow very easily and don't clump together. When you link up monomers into longer segments, you form polymers (long chains of molecules).

Polymers don't flow very easily at all - they tend to get tangled up until you add the cross-linking agent, which buddies up the different segments of the molecule chains together into a climbing-rope design.

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Materials:

Here's what you do:

 

Download Student Worksheet & Exercises

By adding borax to the mix, you cross-link the long chains of molecules together into a fishnet, and the result is a gel we call slime. PVA is used make sponges, hoses, printing inks, and plastic bags.

You can add food coloring (or a bit of liquid Ivory dish soap to get a marbled appearance). You can also add a dollop of titanium dioxide sunscreen to your slime before cross-linking it to get a metallic sheen.

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Bouncy Putty Slime

Wednesday June 30, 2010

The glue is a polymer, which is a long chain of molecules all hooked together like tangled noodles. When you mix the two solutions together, the water molecules start linking up the noodles together all along the length of each noodle to get more like a fishnet. Scientists call this a polymetric compound of sodium tetraborate and lactated glue. We call it bouncy putty.


Here’s what you do:


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  1. Combine ½ cup water with one teaspoon of Borax in a cup and stir with a popsicle stick.
  2. In another cup, mix equal parts white glue and water.
  3. Add in a glob of glue mixture to the borax.
  4. Stir for one second with a popsicle stick, then quickly pull the putty out of cup and play with it until it dries enough to bounce on table (3-5 minutes).
  5. Pick up an imprint from a textured surface or print from a newspaper, bounce and watch it stick, snap it apart quickly and ooze apart slowly.


Download Student Worksheet & Exercises
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Football Ice Cream

Wednesday June 30, 2010

Is it hot where you live in the summer? What if I gave you a recipe for making ice cream that doesn’t require an expensive ice cream maker, hours of churning, and can be made to any flavor you can dream up? (Even dairy-free if needed?)


If you’ve got a backyard full of busy kids that seem to constantly be in motion, then this is the project for you.  The best part is, you don’t have to do any of the churning work… the kids will handle it all for you!


This experiment is simple to set up (it only requires a trip to the grocery store), quick to implement, and all you need to do guard the back door armed with a hose to douse the kids before they tramp back into the house afterward.


One of the secrets to making great ice cream quickly is [am4show have=’p8;p9;p23;p50;p80;p88;p101;’ guest_error=’Guest error message’ user_error=’User error message’ ] to be sure that the milk and cream is COLD.  I will make this particular recipe, it’s usually with hundreds of kids, and our staff will stuff the milk products in the freezer for an hour or two or under hundreds of pounds of ice to make sure it’s super-cold.


If you’re going for the dairy-free kind, simply skip the milk and cream and add a bit of extra time to the chill time of your substitute ‘milk’.  We’ve had the best luck with almond and soy milk. Are you ready?


Here’s what you need:


Materials:


  • 1 quart whole milk (do not substitute, unless your child has a milk allergy, then use soy or almond milk)
  • 1 pint heavy cream (do not substitute, unless your child has a milk allergy, then skip)
  • 1 cup sugar (or other sweetener)
  • 1 tsp vanilla (use non-alcohol kind)
  • rock salt (use table salt if you can’t find it)
  • lots of ice
  • freezer-grade zipper-style bags (you’ll need quart and gallon sizes)


Download Student Worksheet & Exercises


How does that work? Ice cream is basically “fluffy milk”. You need to whip in a lot of air into the milk fat to get the fluffy pockets that make this stuff worthwhile. The more the kids shake the bag, the faster it will turn into ice cream.


Why do we put salt on the ice?


If you live in an area where they put salt on the roads, you already know that people do this to melt the ice. But how does salt melt ice? Think about the chemistry of what’s going on. Water normally freezes at zero degrees Celsius. But salt water presses lower than zero, so the freezing point of salt water is lower than fresh water. By sprinkling salt on the roads, you’re lowering the point at which water freezes at. When you add a solute (salt) to the solvent (water) to alter the freezing point of the solution, it’s known as the “freezing point depression”.


Tips: Don’t use nonfat milk – it won’t work with this style of ice-cream making.  if you’re adding fruit or chocolate bits, make sure you get those cold in advance too, or they will slow down your process as they heat your milk solution. (We usually add those bits last after the ice cream is done.)


IMPORTANT: Do NOT substitute dry ice for the water ice – the carbon dioxide gases build quickly and explode the bag, and now you have flying bits of dry ice that will burn skin upon contact.  That’s not the biggest issue, though… the real problem is that now animals (like your dog) and small children pop a random piece of dry ice into their mouths, which will earn your family a visit to the ER. So stick with the regular ice from your fridge.


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Colored Campfires and Rainbows

Wednesday June 30, 2010

Always have a FIRE EXTINGUISHER and ADULT HELP handy when performing fire experiments. NO EXCEPTIONS.

This video will show you how to transform the color of your flames. For a campfire, simply sprinkle the solids into your flames (make sure they are ground into a fine powder first) and you’ll see a color change. DO NOT do this experiment inside your house – the fumes given off by the chemicals are not something you want in your home!


One of the tricks to fire safety is to limit your fuel. The three elements you need for a flame are: oxygen, spark, and fuel.  To extinguish your flames, you’ll have to either wait for the fuel to run out or smother the flames to cut off the oxygen. When you limit your fuel, you add an extra level of safety to your activities and a higher rate of success to your eyebrows.


Here’s what we’re going to do: first, make your spectrometer: you can make the simple spectrometer or the more-advanced calibrated spectrometer. Next, get your chemicals together and build your campfire. Finally, use your spectrometer to view your flames.


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Download Student Worksheet & Exercises


This experiment is at your own risk!  You MUST get an experienced adult to help you with this activity.

  • Boric Acid or placing a copper pipe directly in the fire will give you GREEN flames
  • Borax (sodium tetraborate) gives a YELLOW-GREEN flame
  • Epsom salts (magnesium sulfate) will give you WHITE-PURPLE flames
  • Table salt (sodium chloride) will give you YELLOW flames
  • Washing soda (sodium carbonate) will give you YELLOW-GREEN flames
  • Calcium Chloride (Ice Melt, Dri-Ez) will give an ORANGE flame (make sure it says ‘Calcium Chloride’ – there are a lot of other types of molecules used to melt ice!)
  • Potassium Chloride (Nu Salt) will give you RAINBOW flames
  • RED flames are made with strontium, which isn’t something you want kids to be playing with.

How to Tell Which Elements are Burning

Once you’ve got the hang of how to make colored flames, your next step is to create a spectroscope.  When you aim your nifty little device at the flames, you’ll be able to split the light into its spectra and see which elements are burning.  For example, if you were to view hydrogen burning with your spectroscope, you’d see the bottom appear in your spectrometer:



Notice how one fits into the other, like a puzzle.  When you put the two together, you’ve got the entire spectrum.


What’s the difference between the two? The upper picture (absorption spectrum of hydrogen) is what astronomers see when they use their spectrometers on distant stars when looking through the earth’s atmosphere (a cloud of gas particles). The lower picture (emission spectrum of hydrogen) is what you’d see if you were looking directly at the source itself.


Note – Do NOT use your spectrometer to look at the sun! When astronomers look at stars, they have computers look for them – they aren’t putting their eye on the end of a tube.


What about other elements?

Each element has it’s own special ‘signature’, unique as a fingerprint, it leaves behind when it burns. This is how we can tell what’s on fire in a campfire. For example, here’s what you’d see for the following elements:


Just get the feel for how the signature changes depending on what you’re looking at.  For example, a green campfire is going to look a lot different from a regular campfire, as you’re burning several elements in addition to just carbon. When you look at your campfire with your spectroscope, you’re going to see all the signatures at the same time.  Imagine superimposing all four sets of spectral lines above (carbon, neon, magnesium, and nitrogen) into one single spectrum… it’s going to look like a mess!  It takes a lot of hard work to untangle it and figure out which lines belong to which element.  Thankfully these days, computers are more than happy to chug away and figure most of it out for us.


Here’s the giant rainbow of absorption lines astronomers see when they point their instruments at the sun:



Do you see all the black lines? Those are called emission lines, and since astronomers have to look through a lot of atmosphere to view the sun, there’s a lot of the spectrum missing (shown by the black lines), especially corresponding to water vapor. The water absorbs certain wavelengths of light, which corresponds to the black lines.


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Sewer Slime

Wednesday June 30, 2010

Guar gum comes from the guar plant (also called the guaran plan), and people have found a lot of different and interesting uses for it.  It’s one of the primary substitutes for fat in low-fat and fat-free foods. Cooks like to  use guar gum in foods as it has 8 times the thickening power of cornstarch, so much less is needed for the recipe. Ice cream makers use it to keep ice crystals from forming inside the carton. Doctors use it as a laxative for their patients.


When we teach kids how to make slime using guar gum, they call it “fake fat” slime, mostly because it’s used in fat-free baking.  You can find guar gum in health food stores or order it online. We’re going to whip up a batch of slime using this “fake fat”. Ready?


Here’s what you do:
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Download Student Worksheet & Exercises


  1. Fill a cup with 7 tablespoons of cold water.
  2. Stir in 1/4 teaspoon of guar gum, stir with a popsicle stick 10 times and stop, leaving the stick in.
  3. Cautiously dip a pinkie into the cup, then rub it in their fingers. Does it smell?
  4. Leave it for 2 minutes to thicken.
  5. In a fresh cup, mix 1 teaspoon borax (sodium tetraborate) in one tablespoon water.
  6. Add ½ teaspoon of the Borax Solution to the Guar solution. Stir and it will form a gel that looks like real boogers!

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Volcanoes

Wednesday June 30, 2010

If you’ve ever wanted to make your own version of a volcano that burps and spit all over the place, then this is the experiment for you.  We used to teach kids how to make genuine Fire & Flame volcanoes, but parents weren’t too happy about the shower of sparks that hit the ceiling and fireballs that shot out of the thing… so we’ve toned it down a bit to focus more on the lava flow.


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FIRST STEP: Make the volcano.


The first thing to do is mix up your own volcano dough. You can choose from the following two mixtures. The Standard Volcano Dough is akin to play dough; the Earthy Volcano Dough looks more like the real thing. Either way, you’ll need a few days on the shelf or a half-hour in a low-temperature oven to bake it dry. Alternatively, you can use a slab of clay for the dough.


  • Standard Volcano Dough Mix together 6 cups flour, 2 cups salt, ½ cup vegetable oil, and 2 cups warm water. The resulting mixture should be firm but smooth. Stand a water or soda bottle in a roasting pan and mold the dough around it into a volcano shape.
  • Earthy Volcano Dough Mix 2½ cups flour, 2½ cups dirt, 1 cup sand, and 1½ cups salt. Add water by the cup until the mixture sticks together. Build the volcano around an empty water bottle on a disposable turkey-style roasting pan. It will dry in two days if you have the time, but why wait? You can erupt when wet if the mixture is stiff enough! (And if it’s not, add more flour until it is.)

SECOND STEP: Create the reaction.


  • Soda Volcanoes Fill the bottle most of the way with warm water and a bit of red food coloring. Add a splash of liquid soap and ¼ cup baking soda. Stir gently. When ready, add vinegar in a steady stream and watch that lava flow.
  • Air Pressure Sulfur Volcanoes Wrap the volcano dough around an 18” piece of clear, flexible tubing. Shape the dough into a volcano and place in a disposable roasting pan. Push and pull the tube from the bottom until the other end of the tube is just below the volcano tip. If you clog the ends of the tubing with clay, just trim away the clog with scissors. Using your fingers, shape the inside top of the volcano to resemble a small paper cup. Your solution needs a chamber to mix and grow in before overflowing down the mountain. The tube goes at the bottom of the clay-cup space. Be sure the volcano is SEALED to the cookie sheet at the bottom. You won’t want the solution running out of the bottom of the volcano instead of popping out the top!
    • Make your chemical reactants.
      • Solution 1: Fill one bucket halfway with warm water and add 1 to 2 cups baking soda. Add 1 cup of liquid dish soap and stir very gently so you don’t make too many bubbles.
      • Solution 2: Fill a second bucket halfway with water and add 1 cup of aluminum sulfate (also called alum; find this in the gardening section of the hardware store or check the spice section of the grocery store). Add red food coloring and stir.
      • Putting it all together: Count ONE (and pour in Solution 1) … TWO (inhale air only!) …… and THREE (pour in Solution 2 as you put your lips to the tube from the bottom of the volcano and puff as hard as you can!) Lava should not only flow but burp and spit all over the place!

Download Student Worksheet & Exercises


Exercises


  1.  How is this activity similar to the volcanoes on Mars?
  2. What gas is produced with this reaction?
  3. Which planets have volcanoes?

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Water Purification

Wednesday June 30, 2010

Ever wonder how the water draining down your sink gets clean again? Think about it: The water you use to clean your dishes is the same water that runs through the toilet.  There is only one water pipe to the house, and that source provides water for the dishwasher, tub, sink, washing machine, toilet, fish tank, and water filter on the front of your fridge.  And there’s only one drain from your house, too!  How can you be sure what’s in the water you’re using?


This experiment will help you turn not only your coffee back into clear water, but the swamp muck from the back yard as well.  Let’s get started.
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  • clean play sand
  • alum (check the spice section of the grocery store)
  • distilled water
  • water sample (a cup of coffee with the ground put back in works great)
  • activated carbon (check an aquarium store)
  • cheese cloth
  • clear disposable cups
  • popsicles
  • medicine dropper or syringe (no needle)
  • funnel
  • 2 cotton balls
  • measuring spoon (1/4 tsp and 1/2 tsp)


Download Student Worksheet & Exercises


There are several steps you need to understand as we go along:


  • Aeration:  Aerate water to release the trapped gas.  You do this in the experiment by pouring the water from one cup to another.
  • Coagulation: Alum collects small dirt particles, forming larger, sticky particles called floc.
  • Sedimentation: The larger floc particles settle to the bottom of the cup.
  • Filtration:  The smaller floc particles are trapped in the layer of sand and cotton.
  • Disinfection:  A small amount of disinfectant is added to kill the remaining bacteria.  This is for informational purposes only — we won’t be doing it in this experiment. (Bleach and kids don’t mix!)

Preparing the Sample

Make your “swamp muck” sample by filling a small pitcher with water, coffee, and the coffee grounds.  Fill up another small pitcher with clean water. In a third small pitcher, pour a small scoop of charcoal carbon and cold water.


Fill one clear plastic cup half full of swamp muck.  Stir in ½ teaspoon aluminum sulfate (also known as alum) and ¼ teaspoon calcium hydroxide (also known as lime; it’s nasty stuff to breathe in so keep it away from kids).  You have just made floc, the heavy stuff that settles to the bottom.


Aside: For pH balance, you can add small amounts of lime to raise the pH (level 7 is optimal), if you have pH indicators on hand (find these at the pharmacy).


Stir it up and sniff — then don’t touch for 10 minutes as you make the filter.


Making the Filter

Grab a cotton ball and fluff it out HUGE.  Then stuff it into the funnel.  The funnel will take two or three balls.  (Don’t stuff too hard, or nothing will get through!) Strain out the carbon granules from the pitcher, and put the black carbon water back into the pitcher.  Place the funnel over a clean cup and pour the black water directly over the cotton balls.  Run the dripped-out water back through the funnel a few times.  Those cotton balls will turn gray-black!  Discard all the carbon water.


Add a layer of sand over the top of the cotton balls. It should cover the balls entirely and come right up to the top of the funnel. Fill a third empty cup half-full of clean water from the pitcher.  Drip (using a dropper) clean water into the funnel. (This gets the filter saturated and ready to filter.)


Showtime!

It’s time to filter the swamp muck.  Without disturbing the sample, notice where the floc is… the dark, solid layer at the bottom.  You’ve already filtered out the larger particles without using a filter!  Using a dropper, take a sample from the layer above the floc (closer to the top of your container) and drip it into the funnel.  If you’ve set up your experiment just right, you’ll see clear water drip out of your funnel.


Continue this process until the liquid starts to turn pale – which indicates that your filter is saturated and can’t filter out any more particles.


To dissect the filter and find out where the muck got trapped, invert the funnel over four layers of paper towel.  Usually the blacker the cotton, the better the filter will work.  Look for coffee grounds in the sand.


“Radioactive” Sample

Activate a disposable light stick. Break open the light stick (use gloves when handling the inner liquid), and using the dropper, add the liquid to the funnel.  You can also drip the neon liquid by the drop into the swamp muck sample and pass it through your filter.


You can test out other types of “swamp muck” by mixing together other liquids (water, orange juice, etc.) and solids (citrus pulp, dirt, etc.).  Stay away from carrot juice, grape juice, and beets — they won’t work with this type of filter.


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Calibrated Spectrometer

Wednesday June 30, 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.

While this spectrometer isn't powerful enough to split starlight, it's perfect for using with the lights in your house, and even with an outdoor campfire.  Next time you're out on the town after dark, bring this with you to peek different types of lights - you'll be amazed how different they really are. You can use this spectrometer with your Colored Campfire Experiment also.

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 the sun’s reflected light on it.

Here's what you do:

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Download Student Worksheet & Exercises

You will need:

  • cardboard box (ours is 10" x 5" x 5", but anything close to this will work fine)
  • linear diffraction grating (you can order one here)
  • 2 razor blades (with adult help)
  • masking tape
  • ruler
  • photocopy of a ruler (or sketch a line with 1 through 10 cm markings on it, about 4cm wide)

1. Using a small box, measure 4.5 cm from the edge of the box. Starting here, cut a hole for the double-razor slit that is 1.5 cm wide 3 cm long.

2. From the other edge (on the same side), cut a hole to hold your scale that is 11 cm wide and 4 cm tall.

3. Print out the scale and attach it to the edge of the box.

4. Very carefully line up the two razors, edge-to-edge to make a slit and secure into place with tape.

5. On the opposite side of the box, measure over 3 cm and cut a hole for the diffraction grating that is 4 cm wide and 3 cm tall.

5. Tape your diffraction grating over the hole.

Aim the razor 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. Put the diffraction grating up to your eye and look at the inner scale.  Move the spectrometer around until you can get the rainbow to be on the scale inside the box.

How to Calibrate the Spectrometer with the Scale Inside your box is a scale in centimeters. Point your slit to a fluorescent bulb, and you'll see three lines appear (a blue, a green, and a yellow-orange line). The lines you see in the fluorescent bulb are due to mercury superimposed on a rainbow continuous spectrum due to the coating. Each of the lines you see is due to a particular electron transition in the visible region of Hg (mercury). The blue line (435 nm), the green line (546 nm), and the yellow orange line (579 nm). (If you look at a sodium vapor street light you'll see a yellow line (actually 2 closely spaced) at 589 nm.)

Step 1. Line the razor slits along the length of the fluorescent tube to get the most intense lines. Move the box laterally (the lines will move due to parallax shift).

Step 2. Take scale readings at the extreme of the these movements and take the average for the scale reading. For instance, if the blue line averages to the 8.8 cm value, this corresponds to the 435 nm wavelength. Do this for the other 2 lines.

Step 3. On graph paper, plot the cm ( the ruler scale values) on the vertical axis and the wavelength (run this from 400-700 nm) on the horizontal axis. Draw the best straight lines thru the 3 points (4 lines if you use the Na (sodium) street lamp). You've just calibrated the spectrometer.

Step 4. Line the razor slits up with another light source.  Notice which lines appear and where they are on your scale.  Find the value on your graph paper. For example, if you see a line appear at 5.5 cm, use your finger to follow along to the 5.5 cm until you hit the best-fit line, and then read the corresponding value on the wavelength axis. You now have the wavelength for the line you've just seen!

Notes on Calibration and Construction: If you swap out different diffraction gratings, you will have to re-calibrate. If you make a new spectrometer, you will have to re-calibrate to the Hg (mercury) lines for each new spectrometer. If you do remake the box, use a scale that is translucent so you can see the numbers. If you use a clear plastic ruler, it may let in too much light from the outside making it difficult to read the emission line.

What other light sources work? 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. When you walk down town at night and look at various "neon" signs. Ne (neon) is a real burner! Do this with a friend who is willing to vouch for your sanity.

Question: What happens when you aim a laser through a diffraction grating? (See picture above - can you find the two dots on either side of the main later dot?)

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Pinhole Solar Projector

Wednesday June 30, 2010

You might be curious about how to observe the sun safely without losing your eyeballs. There are many different ways to observe the sun without damaging your eyesight. In fact, the quickest and simplest way to do this is to build a super-easy pinhole camera that projects an image of the sun onto an index card for you to view.


CAUTION: DO NOT LOOK AT THE SUN THROUGH ANYTHING WITH LENSES!!


This simple activity requires only these materials:


  • tack
  • 2 index cards (any size)
  • sunlight

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Here’s what you do:



 
Download Student Worksheet & Exercises


With your tack, make a small hole in the center of one of the cards. Stack one card about 12″ above the over and go out into the sun. Adjust the spacing between the cards so a sharp image of the sun is projected onto the lower paper. The sun will be about the size of a pea.


You can experiment with the size of the hole you use to project your image. What happens if your hole is really big? Too small? What if you bend the lower card while viewing? What if you punch two holes? Or three?


Exercises


  1.  How many longitude degrees per day does the sunspot move?
  2.  Do all sunspots move at the same rate?
  3.  Did some of the sunspots change size or shape, appear or disappear?

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Streaming Water

Tuesday June 1, 2010

Fill the bathtub and climb in. Grab your water bottle and tack and poke several holes into the lower half the water bottle. Fill the bottle with water and cap it. Lift the bottle above the water level in the tub and untwist the cap. Water should come streaming out. Close the cap and the water streams should stop. Open the cap and when the water streams out again, can you “pinch” two streams together using your fingers?


Materials: A tack, and a plastic water bottle with cap, and bathtub


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What’s happening? First, you’re getting clean. Second, you’re playing with pressure again. Watch the water level when you uncap the bottle. As the water streams out, the water level in the bottle moves downward. Notice how the space for air increases in the top of the bottle as the water line moves down. (The air comes in through the mouth of the bottle.) When you cap on the bottle, there’s no place for air to enter the bottle. The water line wants to move down, but since there’s no incoming air to equalize the pressure, the flow of water through the holes stops. Technically speaking, there’s a small decrease in pressure in the air pocket in the top of the bottle and therefore the air outside the bottle has a higher pressure that keeps the water in the bottle. Higher pressure pushes!


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Sneaky Bottles

Tuesday June 1, 2010

This experiment illustrates that air really does take up space! You can’t inflate the balloon inside the bottle without the holes, because it’s already full of air. When you blow into the bottle with the holes, air is allowed to leak out making room for the balloon to inflate. With the intact bottle, you run into trouble because there’s nowhere for the air already inside the bottle to go when you attempt to inflate the balloon.


You’ll need to get two balloons, one tack, and two empty water bottles.


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Poke a balloon into a water bottle and stretch the balloon’s neck covering the mouth of the bottle from the inside. Repeat with the other bottle. Using the tack, poke several small holes in the bottom of one of the water bottles. Putting your mouth to the neck of each bottle, try to inflate the balloons.


A cool twist on this activity is to drill a larger hole in the bottle (say, large enough to be covered up by your thumb) and inflate the balloon inside the bottle with hole open, then plug up the hole with your thumb. The balloon will remain inflated even though its neck is not tied! Where is the higher pressure region now?


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Squished Balloon

Tuesday June 1, 2010

Fire eats air, or in more scientific terms, the air gets used up by the flame and lowers the air pressure inside the jar. The surrounding air outside the jar is now at a higher pressure than the air inside the jar and it pushes the balloon into the jar. Remember: Higher pressure pushes!


Materials: a balloon, one empty glass jar, scrap of paper towel , matches with an adult


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Blow up a balloon so that it is just a bit larger than the opening of the jar and can’t be easily shoved in. With an adult, light the small wad of paper towel on fire and drop it into the jar. Place the balloon on top. When the fire goes out, lift the balloon. The jar goes with it!


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Fountain Bottle

Tuesday June 1, 2010

As you blow air into the bottle, the air pressure increases inside the bottle. This higher pressure pushes on the water, which gets forced up and out the straw (and up your nose!).


Materials: small lump of clay, water, a straw, and one empty 2-liter soda bottle.


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Fill a 2-liter soda water bottle full of water and seal it with a lump of clay wrapped around a long straw so that the straw is secured to the mouth of the bottle. (The straw should be partly submerged in the water.) Blow hard into the straw. Splash!



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Bubble Experiments

Monday May 31, 2010
Magician Tom Noddy

If you’re fascinated by the simple complexity of the standard soap bubble, then this is the lab for you. You can easily transform these ideas into a block-party Bubble Festival, or just have extra fun in the nightly bathtub. Either way, your kids will not only learn about the science of water, molecules, and surface tension, they’ll also leave this lab cleaner than they started (which is highly unusually for science experiments!)


Soap also makes water stretchy. If you’ve ever tried making bubbles with your mouth just using spit, you know that you can’t get the larger, fist-sized spit bubbles to form completely and detach to float away in the air. Spit is 94% water, and water by itself has too much surface tension, too many forces holding the molecules together. When you add soap to it, they relax a bit and stretch out. Soap makes water stretch and form into a bubble.
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Download Student Worksheet & Exercises


The absolute best time to make gigantic bubbles is on an overcast day, right after it rains. Bubbles have a thin cell wall that evaporates quickly in direct sun, especially on a low-humidity day. If you live in a dry area with low-humidity, be sure to use glycerin. The glycerin will add moisture and deter the rapid thinning of the bubble’s cell wall (which cause bubbles to tear and pop).


Best Bubble Solution Gently mix together 6 cups cold water in a shallow tub with 1 cup green Dawn (or clear Ivory) dish soap.  If it’s a hot, dry day, add a few tablespoons of glycerin. (Glycerin can be found at the drugstore.)  If you’re finding the solution too thin, add a second cup of dish soap. You can add all sorts of things to find the perfect soap solution:  lemon juice, sugar, corn syrup, Karo syrup, maple syrup, glycerin — to name just a few.  Each will add its own properties to the bubble solution.  (You can have buckets of each variation along with plain dish soap and water to compare.) You can reduce the water, increase the soap, etc… but here’s a good starting point: 2 cups dish soap with 1 cup Karo syrup and 6 cups cold water.


Zillions of Tiny Bubbles can be made with strawberry baskets.  Simply dip the basket into the bubble solution and twirl around.  You can also use plastic six-pack soda can holders.


Trumpet Bubbles are created by using a modified water bottle.  Cut off the bottom of the bottle, dip the large end in the soap solution, put the small end to your lips, and blow.  You can separate the bubble from the trumpet by rolling the large end up and away from your bubble.


Bubble Castles are built with a straw and a plate. First, spread bubble solution all over a smooth surface (such as a clean cookie sheet, plate, or tabletop).  Dip one end of a straw in the bubble solution and blow bubbles all over the surface.  Make larger domes with smaller ones inside.  Notice how the bubbles change shape and size when they connect with others.


Stretch and Squish! Get one hand-sized bubble in each hand.  Slap them together (so they join, not pop!).  What if you join them s l o w l y?


Light Show is always a favorite.  Find a dark room. Find a BIG flashlight and stand it on end. Rub soap solution all over the bottom of an uncolored plastic lid (such as from a coffee can). Balance the lid, soapy side up, on the flashlight (or on the spring-type clothespins).  Blow a hemisphere bubble on top of the lid.  Blow gently along the side of the bubble. Watch the colors swirl.


Weird Shapes are the simplest way to show how soap makes water stretchy.  Dip a rubber band completely in the soap solution and pull it up.  Stretch the rubber band using your fingers.  Twist and tweak into all sorts of shapes.  Note that the bubble always finds a way of filling the shape with the minimum amount of surface area.  Make a Moebius bubble by cutting a thick ribbon, giving one end a half-twist, and reattaching the ends (by sewing, stapling, or taping).


Polygon Shapes allow you to make square and tetrahedral bubbles.  Create different 3-D shapes by bending pipe cleaners into cubes, tetrahedrons, or whatever you wish. Alternatively, you can use straws threaded onto string to make 3-D triangular shapes.  Notice how the film always finds its minimum surface area.  Can you make square bubbles?


Gigantic Bubbles Using the straws and string, thread two straws on three feet of string and tie off.  Grasp one straw in each hand and dip in soap solution.  Use a gentle wind as you walk to make BIG bubbles.  Find air thermals (warm pockets of air) to take your bubbles up, up, UP!


Kid-in-a-Bubble Pour your best bubble solution into a child’s plastic swimming pool.  Lay a Hula-hoop down, making sure there is enough bubble solution to just cover the hoop. Have your child stand in the pool (use a stool if you want to avoid wet feet), and lift the hoop! For a more permanent project, use an old car tire sliced in half lengthwise (the hard way) to hold the bubble solution. The kid stands in the hole and doesn’t get wet!


Electric Bubbles Blow some fist-sized bubbles and set them loose. Rub an inflated balloon on your head or wool sweater to charge the balloon and get the charged balloon close to a soap bubble. If you are fast and careful enough, you can steer the bubble around the room.


Hover Bubbles Since bubbles are light, you can float them on a gas that is slightly denser than the air they are filled with, such as carbon dioxide. Place a shallow glass dish inside a larger glass dish or tank (like an unoccupied aquarium). Into the smaller dish, add two cups vinegar and one cup baking soda.


After the fizzing has subsided, your larger container is now filled with carbon dioxide gas. Make sure it’s away from drafts or movement so the invisible carbon dioxide gas stays in there. Gently blow bubbles near the opening so they settle into the large tank.  (Don’t blow directly into the container, or you’ll slosh out the CO2.) Your bubbles will hover in the tank so you can have a closer look. What colors do you see? Do the colors change? Does the bubble stay in one place, rise, sink, or move around? If your bubble stays in the tank without popping, you’ll notice that it slowly becomes larger!


Mammoth Bubbles To create bubbles the size of a small car, use your lace trim.  Knot the ends together to form a large loop, and dip your lace into the bubble solution. Gently pick up the loop with your hands about two feet apart, the rest dangling below.  You should see a thin bubble film in the loop.  Keep your hands spread apart and walk (keeping the bottom loop above the ground), and a bubble will form behind you.  When it’s big enough, close the loop by bringing your hands together to seal off the bubble. You can also spin slowly in a circle to put yourself inside a “bubble-bagel” (mathematical term for this shape: toroid). If you do this in a place with warm updrafts (like next to a building), your bubbles will float up and away and quite possibly attract a small crowd… like the photo below.


The How and Why Explanation If you pour a few droplets of water onto a sweater or fabric, you’ll notice that the water will just sit there on the surface in a ball (or oval, if the drop is large enough).  If you touch the ball of water with a soapy finger, the ball disappears into the fibers of the fabric!  What happened?


Soap makes water “wetter” by breaking down the water’s surface tension by about two-thirds.  Surface tension is the force that keeps the water droplet in a sphere shape.  It’s the reason you can fill a cup of water past the brim without it spilling over. Without soap, water can’t get into the fibers of your clothes to get them clean. That’s why you need soap in the washing machine.


Soap also makes water stretchy. If you’ve ever tried making bubbles with your mouth just using spit, you know that you can’t get the larger, fist-sized spit bubbles to form completely and detach to float away in the air. Spit is 94% water, and water by itself has too much surface tension, too many forces holding the molecules together.  When you add soap to it, they relax a bit and stretch out.  Soap makes water stretch and form into a bubble.


The soap molecule looks a lot like a snake; it’s a long chain that has two very different ends.  The head of the snake loves water, and the tail loves dirt.  When the soap molecule finds a dirt particle, it wraps its tail around the dirt and holds it.


The different colors of a soap bubble come from how the white light bounces off the bubble into your eye. Some of the light bounces off the top surface of the bubble and bends only a little bit, while the rest passes through the thin film and bounces off the inner surface of the bubble and refracts more.


If you made the Hover Bubbles, you’ll notice that the bubbles slowly get larger the longer they live in the tank.  Remember that the bubble is surrounded by CO2 gas as it sinks. The bubble grows because carbon dioxide seeps through the bubble film faster than the air seeps out, as CO2 is more soluble in water than air (meaning that CO2 mixes more easily with water than air does).


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Ping Pong Funnel

Monday May 31, 2010

As you blow into the funnel, the air under the ball moves faster than the other air surrounding the ball, which generates an area of lower air pressure. The pressure under the ball is therefore lower than the surrounding air which is, by comparison, at a higher pressure. This higher pressure pushes the ball back into the funnel, no matter how hard you blow or which way you hold the funnel. The harder you blow, the more stuck the ball becomes. Cool.


Materials: A funnel and a ping pong ball


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Insert a ping pong ball into a funnel. Place the stem of the funnel between your lips and tilt your head back so ball stays inside. Blow a strong, long stream of air into the funnel.


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Magic Water Glass Trick

Monday May 31, 2010

Where’s the pressure difference in this trick?


At the opening of the glass. The water inside the glass weighs a pound at best, and, depending on the size of the opening of the glass, the air pressure is exerting 15-30 pounds upward on the bottom of the card. Guess who wins? Tip, when you get good at this experiment, try doing it over a friend’s head!


Materials: a glass, and an index card large enough to completely cover the mouth of the glass.


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Fill a glass one-third with water. Cover the mouth with an index card and over a sink invert the glass while holding the card in place. Remove your hand from the card. Voila! Because atmospheric air pressure is pushing on all sides of both the glass and the card, the card defies gravity and “sticks” to the bottom of the glass. Recall that higher pressure pushes and when you have a difference in pressure, things move. This same pressure difference causes storms, winds, and the index card to stay in place.


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Hot Air Balloon

Monday May 31, 2010

About 400 years ago, Leonardo da Vinci wanted to fly… so he studied the only flying things around at that time: birds and insects. Then he did what any normal kid would do—he drew pictures of flying machines!


Centuries later, a toy company found his drawing for an ornithopter, a machine that flew by flapping its wings (unlike an airplane, which has non-moving wings). The problem (and secret to the toy’s popularity) was that with its wing-flapping design, the ornithopter could not be steered and was unpredictable: It zoomed, dipped, rolled, and looped through the sky. Sick bags, anyone?


Hot air balloons that took people into the air first lifted off the ground in the 1780s, shortly after Leonardo da Vinci’s plans for the ornithopter took flight. While limited seating and steering were still major problems to overcome, let’s get a feeling for what our scientific forefathers experienced as we make a balloon that can soar high into the morning sky.


Materials: A lightweight plastic garbage bag, duct or masking tape, a hand-held hair dryer. And a COLD morning.


Here’s what you do:


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Shake out a garbage bag to its maximum capacity. Using duct or masking tape, reduce the opening until it is almost-closed leaving only a small hole the size of the hair dryer nozzle. Use the hair dryer to inflate the bag, heating the air inside, but make sure you don’t melt the bag! When the air is at its warmest, release your hold on the bag while at the same time you switch off the hair dryer. The bag should float upwards and stay there for a while.


Troubleshooting: This experiment works best on cold, windless mornings. If it’s windy outside, try a cool room. The greater the temperature difference between the hot air inside the garbage bag versus the cold, still air, the faster the bag rises. The only other thing to watch for is that you’ve taped the mouth of the garbage bag securely so the hot air doesn’t seep out. Be sure the opening you leave is only the diameter of your hair dryer’s nozzle.


Want to go BIGGER? Then try the 60-foot solar tube!
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Diaper Wind Bag

Monday May 31, 2010

Lots of science toy companies will sell you this experiment, but why not make your own? You’ll need to find a loooooong bag, which is why we recommend a diaper genie. A diaper genie is a 25′ long plastic bag, only both ends are open so it’s more like a tube. You can get three 8-foot bags out of one pack.


Kids have a tendency to shove the bag right up to their face and blow, cutting off the air flow from the surrounding air into the bag. When they figure out this experiment and perform it correctly, this is one of those oooh-ahhh experiments that will leave your kids with eyes as big as dinner plates.


Here’s what you do:


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Cut an eight-foot section of the diaper genie bag and knot one of the ends. Hold the other end open, take a deep breath, and blow. How many breaths does it take for you to fill up the entire bag with air? Try this now…


After you know how many breaths it takes, do you think you can fill the bag with only ONE breath? The answer is YES! Hold the bag about eight inches from the face and blow long and steady into the bag. As soon as you run out of air, close the end of the bag and slide your hand along the length (toward the knotted end) until you have an inflated blimp.


Troubleshooting: If the bag tears open, use packing tape to mend it.


What’s going on? When you blow air past your lips, a pocket of lower air pressure forms in front of your face. The stronger you blow, the lower the air pressure pocket. The air surrounding this lower pressure region is now at a higher pressure than the surrounding air, which causes things to shift and move. When you blow into the bag (keeping the bag a few inches from your face), you build a lower pressure area at the mouth of the bag, and the surrounding air rushes forward and into the bag.


Substitution Tip: If you can’t locate a diaper genie, you can string together plastic sheets from garbage bags, using lightweight tape to secure the seams. You’ll need to make a 8-12” diameter by eight-foot long tube and close one end. When kids get their eight-foot bag inflated in just one breath, ask them: “Did you really have that much air in your lungs?”


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Genie in a Bottle

Monday May 31, 2010

While this isn’t actually an air-pressure experiment but more of an activity in density, really, it’s still a great visual demonstration of why Hot Air Balloons rise on cold mornings.


Imagine a glass of hot water and a glass of cold water sitting on a table, side by side. Now imagine you have a way to count the number of water molecules in each glass. Which glass has more water molecules?


The glass of cold water has way more molecules… but why? The cold water is more dense than the hot water. Warmer stuff tends to rise because it’s less dense than colder stuff and that’s why the hot air balloon in experiment 1.10 floated up to the sky.


Clouds form as warm air carrying moisture rises within cooler air. As the warm, wet air rises, it cools and begins to condense, releasing energy that keeps the air warmer than its surroundings. Therefore, it continues to rise. Sometimes, in places like Florida, this process continues long enough for thunderclouds to form. Let’s do an experiment to better visualize this idea.


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Materials: Two identical tall glasses, hot water, cold water, red and blue food dye, and an index card larger enough to cover the opening of the glasses



Fill two identical water glasses to the brim: one with hot water, the other with cold water. Put a few drops of blue dye in the cold water, a few drops of red dye in the hot water. Place the index card over the mouth of the cold water and invert the glass over the glass of hot water. Line up the openings of both glasses, and slowly remove the card.


Troubleshooting: Always invert the cold glass over the hot glass using an index card to hold the cold water in until you’ve aligned both glasses. You can also substitute soda bottles for water glasses and slide a washer between the two bottles to decrease the flow rate between the bottles so the effect lasts longer.


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Soda Can Trick

Monday May 31, 2010

When air moves, the air pressure decreases. This creates a lower air pressure pocket right between the cans relative to the surrounding air. Because higher pressure pushes, the cans clink together. Just remember – whenever there’s a difference in pressure, the higher pressure pushes.


You will need about 25 straws and two empty soda cans or other lightweight containers


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Lay a row of straws parallel to each other on a smooth tabletop. Place two empty soda cans on the straws about an inch apart. Lower your nose to the cans and blow hard through the space between the two cans.


Clink! They should roll toward each other and touch!


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Going Further with Advanced Chemistry

Monday May 31, 2010

This experiment is for advanced students.


One of my best teaching tools for science developed from a brain freeze one afternoon in class. I went to the board to draw the chlorophyll wheel and drew a complete blank.


“Let’s say I forgot how to draw the wheel.” I turned to the class, marker in hand, and scanned the room. Puzzled faces, the blank faces I expected, but, what was that? A few smiles scattered about the room.


As I pulled out and some volunteered info, we got into that wheel. They also found that it was easier to know what to do next than to have me tell them to find it in their book and be prepared…I was coming back to them. Students frantically finding the wheel in their biology books so they were armed when I came to them.


It was a great experience, and my lectures were a lot more fun and interactive from then on.


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Next, I started designing labs that way. Pre-reading was suggested, but they never read for homework…everybody knows that. But they soon found out why they should start reading ahead.


They came in for their lab.


There were a lot of lab supplies out on the counter. I had put all the supplies they would need on the counter. In addition, I put an equal number of supplies out that had nothing to do with the experiment. A problem was written at the top of the board such as, “We need to extract chlorophyll from the leaves on the counter.” And that was it. No lab book, they were on their own.


I gave a short lecture to bait their brains into remembering something and turned them loose. It took a couple of weeks, but I gained so much with them. Many more were reading at home to prepare for the lab, because they didn’t want to sit around trying to figure things out from scratch. They already had an idea on how to do the lab when they came on lab day. If they did not finish in the class time allotted, it was too bad. They could make up the lab later, but most just took the bad grade.


Many more students were motivated beyond my wildest expectations. Many students that were working hard to stay on the bottom started to feel a little peer pressure to help out. Students enjoyed the discovery…..they enjoyed the labs. No more cookie cutter labs for us.


Perhaps some labs in your curriculum could be designed to work this way as a way to provide more advanced learning in the sciences?



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Air Takes Space

Monday May 31, 2010

You’re about to play with one of the first methods of underwater breathing developed for scuba divers hundreds of years ago.! Back then, scientists would invert a very large clear, bell-shaped jar over a diver standing on a platform, then lower the whole thing into the water. Everyone thought this was a great idea, until the diver ran out of breathable air…


Materials: 12″ flexible tubing, two clear plastic cups, bathtub


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Part I: Fill the tub and climb in. Plunge one cup underwater so it fills completely with water. While the cup is underwater, point its mouth downward. Insert one end of the tubing into the cup and blow hard into the other end. The water is forced out of the cup!


Part II: While still in the tub, invert one cup (mouth downwards) and plunge it into the tub so that air gets trapped inside the cup. Place the second cup in the water so it fills with water. Invert the water-filled cup while underwater and position it above the first cup so when you tilt the first cup to release the air bubbles, they get trapped inside the second cup. Here you see that air takes space, because in both variations of this experiment the air forced the water out of the cups.


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Solar Cookies

Saturday May 1, 2010

Can you use the power of the sun without using solar cells? You bet! We’re going to focus the incoming light down into a heat-absorbing box that will actually cook your food for you.


Remember from Unit 9 how we learned about photons (packets of light)?  Sunlight at the Earth’s surface is mostly in the visible and near-infrared (IR) part of the spectrum, with a small part in the near-ultraviolet (UV). The UV light has more energy than the IR, although it’s the IR that you feel as heat.


We’re going to use both to bake cookies in our homemade solar oven. There are two different designs – one uses a pizza box and the other is more like a light funnel. Which one works best for you?


  • Two large sheets of poster board (black is best)
  • Aluminum foil
  • Plastic wrap
  • Black construction paper
  • Cardboard box
  • Pizza box (clean!)
  • Tape & scissors
  • Reusable plastic baggies
  • Cookie dough (your favorite)

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Download Student Worksheet & Exercises


How does that work? Your solar cooker does a few different things. First, it concentrates the sunlight into a smaller space using aluminum foil. This makes the energy from the sun more potent. If you used mirrors, it would work even better!


You’re also converting light into heat by using the black construction paper. If you’ve ever gotten into car with dark seats, you know that those seats can get HOT on summer days! The black color absorbs most of the sunlight and transforms it into heat (which boosts the efficiency of your solar oven).


By strapping on a plastic sheet over the top of the pizza-box cooker, you’re preventing the heat from escaping and cooling the oven off. Keeping the cover clear allows sunlight to enter and the heat to stay in. (Remember the black stuff converted your light into heat?) If you live in an area that’s cold or windy, you’ll find this part essential to cooking with your oven!


Here’s another type of solar cooker that uses a cone design to focus the energy straight to your cookies!



Exercises Answer the questions below:


  1. Name the type of heat energy that the sun provides:
    1. Convection
    2. Conduction
    3. Radiation
    4. Invection
  2. What are some ways that the sun’s energy can be directly harnessed?
  3. Name three of the different parts of the electromagnetic spectrum:

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Solar Boat

Saturday May 1, 2010

expansionpacks_clip_image004_0000Does it really matter what angle the solar cell makes with the incoming sunlight? If so, does it matter much? When the sun moves across the sky, solar cells on a house receive different amounts of sunlight. You’re going to find out exactly how much this varies by building your own solar boat.


We’re going to use solar cells and the basic ideas from Unit 10 (Electricity & Robotics) to build a solar-powered race car.  You’ll need to find these items below.  Note – if you have trouble locating parts, check the shopping list for information on how to order it straight from us.


  • Solar motor
  • Solar cell
  • Foam block (about 6” long)
  • Alligator clip leads
  • Propeller (you can rip one off an old small personal fan or old toy, or find them at hobby stores)

Here’s what you do:


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Download Student Worksheet & Exercises


1. Attach the wires of the solar cell to the motor (one to each motor terminal).


2. Attach the propeller to your motor. If the shaft won’t fit, drill out the center hole. If the hole is too large, use a tiny dab of hot glue on the shaft tip to secure the propeller into place.


3. Stand out in the sun. How do you need to hold your solar cell to make the propellers pin the fastest?


4. Position the motor on a block of foam so that the propeller hangs off the edge and is free to rotate. Hot glue the motor into place, being careful not to get any hot glue near any vents in your motor.


5. Hot glue your solar cell to the foam block. You might want to check the final position in sunlight before attaching it.


6. Optional: Wire up a simple switch (from Unit 10) using paperclips and brass fasteners so you can easily turn your power on and off.


Going further: Using the same solar cell, you can also build a Wind Turbine and a Solar Car.


Exercises Answer the questions below:


  1. What kind of electricity comes from a battery and photovoltaic cell?
    1. Nuclear
    2. Voltaic
    3. Electrochemical
    4. Ionized
  2. Electricity is another name for the free flow of:
    1. Protons
    2. Quarks
    3. Electrodes
    4. Electrons
  3. True or false: Ions are attracted to the same charge.
    1. True
    2. False
  4. Do solar panels work in cloudy climates?
    1. Yes
    2. No

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Solar Car

Saturday May 1, 2010

solarboatSolar energy (power) refers to collecting this energy and storing it for another use, like driving a car. The sun blasts 174 x 1015 watts (which is 174,000,000,000,000,000 watts) of energy through radiation to the earth, but only 70% of that amount actually makes it to the surface. And since the surface of the earth is mostly water, both in ocean and cloud form, only a small fraction of the total amount makes it to land.


A solar cell converts sunlight straight into electricity. Most satellites are powered by large solar panel arrays in space, as sunlight is cheap and readily available out there. While solar cells seem ‘new’ and modern today, the first ones were created in the 1880s, but were a mere 1% efficient. (Today, they get as high as 35%.) A solar cell’s efficiency is a measure of how much sunlight the cell converts into electrical energy.


We’re going to use solar cells and the basic ideas from Unit 10 (Electricity & Robotics) to build a solar-powered race car.  You’ll need to find these items below.  Note – if you have trouble locating parts, check the shopping list for information on how to order it straight from us.


  • Solar cell
  • Solar motor
  • Foam block (about 6” long)
  • Alligator clip leads
  • 2 straws (optional)
  • 2 wooden skewers (optional)
  • 4 milk jug lids or film can tops
  • Set of gears, one of which fits onto your motor shaft (most solar motor kits come with a set), or rip a set out of an old toy

Here’s what you do:


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Download Student Worksheet & Exercises


How does a solar cell work? Solar cells are usually made of silicon. Sunlight is made of packets of energy called photons (we covered this in Unit 9). When photons hit the silicon, one of three things can happen: the photons can pass straight through the silicon if they have a low enough energy; they can get reflected off the surface; or (and this is the fun part) they get absorbed and the electrons in the silicon get knocked out of their shell.


Once knocked out of orbit, the free electrons start flowing through the silicon to create electricity. The solar cells are structured is such a way as to keep the electricity flowing only in one direction. The electron flow created is DC current (refer to Unit 10).


The solar cells you can buy from stores require huge amounts of energy in creating the solar cell, which is the primary downside. You need high temperatures, big vacuum pumps, and lots of people to make a set of solar cells. However, if we focus just on the physics of the solar cell, then we can easily create our own solar battery and other solar cell projects using household items. While these cells won’t look as spiffy as the ones from the store, they still produce electricity from sunlight.


Using the same solar cell, you can also build a Wind Turbine and a Solar Boat.


Exercises Answer the questions below:


  1. Most solar cells are made of what material?
    1. Hydrogen
    2. Aluminum
    3. Silicon
    4. Titanium
  2. Name one benefit of solar cells and one drawback of using them for electricity.
    1. Benefit:
    2. Drawback:
  3. Electrical current begins flowing when:
    1. Sunlight hits an atom
    2. Electrons are knocked out of orbiting atoms
    3. Protons get charged
    4. An atom’s nucleus splits

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Wind Turbine

Saturday May 1, 2010

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Believe it or not, most of the electricity you use comes from moving magnets around coils of wire! Wind turbines spin big coils of wire around very powerful magnets (or very powerful magnets around big coils of wire) by capturing the flow.


Here’s how it works: when a propeller is placed in a moving fluid (like the water from your sink or wind from your hair dryer), the propeller turns. If you attach the propeller to a motor shaft, the motor will rotate, which has coils of wire and magnets inside. The faster the shaft turns, the more the magnets create an electrical current.


The electricity to power your computer, your lights, your air conditioning, your radio or whatever, comes from spinning magnets or wires! Refer to Unit 11 for more detail about how moving magnets create electricity.


We’re going to build a wind turbine that will actually give you different amounts of electricity depending on which way your propeller is facing. Ready?


You’ll need to find these items below.  Note – if you have trouble locating parts, check the shopping list for information on how to order it straight from us.


  • A digital Multimeter
  • Alligator clip leads
  • 1.5-3V DC Motor
  • 9-18VDC Motor
  • Bi-polar LED
  • Foam block (about 6” long)
  • Propeller from old toy or cheap fan, or balsa wood airplane

Here’s what you do:


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Download Student Worksheet & Exercises


Using the same solar cell, you can also build a Solar Car and a Solar Boat.


Exercises


  1. True or false: Electricity in a wind turbine is created by magnets in the turbine:
    1. True
    2. False
  2. What is one advantage of using wind for electricity?
  3.  What might be one problem with constructing wind farms to meet all our energy needs?

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Marshmallow Roaster

Saturday May 1, 2010

Do you like marshmallows cooked over a campfire? What if you don’t have a campfire, though? We’ll solve that problem by building our own food roaster – you can roast hot dogs, marshmallows, anything you want. And it’s battery-free, as this device is powered by the sun.


NOTE: This roaster is powerful enough to start fires! Use with adult supervision and a fire extinguisher handy.


If you’re roasting marshmallows, remember that they are white – the most reflective color you can get.  If you coat your marshmallows with something darker (chocolate, perhaps?), your marshmallow will absorb the incoming light instead of reflecting it.


Here’s what you need to get:


  • 7×10” page magnifier (Fresnel lens)
  • Cardboard box, about a 10” cube
  • Aluminum foil
  • Hot glue, razor, scissors, tape
  • Wooden skewers (BBQ-style)
  • Chocolate, marshmallows, & graham crackers

Here’s what you do:



Download Student Worksheet & Exercises


How does it do that? The Fresnel lens is a lot like a magnifying glass.  In Unit 9, we learned how convex lenses are thicker in the middle (you can feel it with your fingers).  A Fresnel lens (first used in the 1800s to focus the beam in a lighthouse) has lots of ridges you can feel with your fingers.  It’s basically a series of magnifying lenses stacked together in rings (like in a tree trunk) to magnify an image.


The best thing about Fresnel lenses is that they are lightweight, so they can be very large (which is why light houses used these designs). Fresnel lenses curve to keep the focus at the same point, no matter close your light source is.


The Fresnel lens in this project is focusing the incoming sunlight much more powerfully than a regular hand held magnifier. But focusing the light is only part of the story with your roaster.  The other part is how your food cooks as the light hits it.  If your food is light-colored, it’s going to cook slower than darker (or charred) food. Notice how the burnt spots on your food heat up more quickly!


Scientifically Dissecting a Marshmallow

Plants take in energy (from the sun), water, and carbon dioxide (which is carbon and oxygen) and create sugar, giving off the oxygen. In other words: carbon + water + energy = sugar


  1. In this experiment, we will reverse this equation, by roasting a marshmallow, which is mostly sugar.
  2. When you roast your marshmallow, first notice the black color. This is the carbon.
  3. Next notice the heat and light given off. These are two forms of energy.
  4. Finally, put the roasting marshmallow if a mason jar. Notice that condensation forms on the sides. This is the water.

So, by roasting the marshmallow, we showed: sugar = carbon + water + energy!


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Steamboats

Saturday May 1, 2010

In 1920’s, these were a big hit. They were originally called “Putt Putt Steam Boats”, and were fascinating toys for adults and kids alike. We’ll be making our own version that will chug along for hours. This is a classic demonstration for learning about heat, energy, and how to get your kids to take a bath.



Here’s what you need to build your own:


  • Copper tubing (1/8”-1/4” dia x 12” long)
  • Votive candle
  • Foam block
  • Scissors or razor (with adult help)
  • Bathtub

Here’s what you need to do:



Download Student Worksheet & Exercises


  1. Wrap the copper tubing 2-3 times around a thick marker. You want to create a ‘coil’ with the tubing. Do this slowly so you don’t kink the tubing. End with two 3” parallel tails. (This is easier if you start in the middle of the tubing and work outwards in both directions.)
  2. Stick each tail through a block of foam. Bend the wires to they run along the length of the bottom of the boat, slightly pointed upwards. (You can also use a plastic bottle cut in half.)
  3. Position a votive candle on the topside of the boat and angle the coil so it sits right where the flame will be.
  4. To start your boat, fill the bathtub with water. While your tub fills, hold the tubing in the running water and completely fill the coil with water.
  5. Have your adult helper light the candle. In a moment, you should hear the ‘putt putt’ sounds of the boat working!
  6. Troubleshooting: if your boat doesn’t work, it could be a few things:
    1. The tubing has an air bubble. In this case, suck on one of the ends like a straw to draw in more water. Heating an air bubble will not make the boat move – it needs to be completely filled with water.
    2. Your coil is not hot enough. You need the water to turn into steam, and in order for this to happen, you have to heat the coil as hot as you can. Move the coil into a better position to get heat from the flame.
    3. The exhaust pipes are angled down. You want the stem to move up and out of your pipes, not get sucked back in. Adjust the exit tubing tails so they point slightly upwards.

How Do They Work? Your steam boat uses a votive candle as a heat source to heat the water inside the copper tubing (which is your boiling chamber). When the water is heated to steam, the steam pushes out the tube at the back with a small burst of energy, which pushes the boat forward.


Since your chamber is small, you only get a short ‘puff’ of energy. After the steam zips out, it creates a low pressure where it once was inside the tube, and this draws in fresh, cool water from the tub. The candle then heats this new water until steam and POP! it goes out the back, which in turn draws in more cool water to be heated… and on it goes. The ‘clicking’ or ‘putt putt’ noise you hear is the steam shooting out the back. This is go on until you either run out of water or heat.


Bonus! Here’s a video from a member that colored the water inside the pipe so they could see when it got pushed out! Note that the boat usually runs as fast as the first video on this page. The boats here are getting warmed up, ready to go, so they only do one or two puffs before they really start up.



Exercises Answer the questions below:


  1. Name three sources of renewable or alternative energy:
  2. Why is it important to look for renewable sources of energy?
  3. What is one example of a fossil fuel?

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Solar Battery

Saturday May 1, 2010

This is the kind of energy most people think of when you mention ‘alternative energy’, and for good reason! Without the sun, none of anything you see around you could be here. Plants have known forever how to take the energy and turn it into usable stuff… so why can’t we?


The truth is that we can. While normally it takes factories the size of a city block to make a silicon solar cell, we’ll be making a copper solar cell after a quick trip to the hardware store. We’re going to modify the copper into a form that will allow it to react with sunlight the same way silicon does. The image shown here is the type of copper we’re going to make on the stovetop.


This solar cell is a real battery, and you’ll find that even in a dark room, you’ll be able to measure a tiny amount of current. However, even in bright sunlight, you’d need 80 million of these to light a regular incandescent bulb.


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You’ll need to gather these materials together:


  • ½ sq. foot of copper flashing sheet (check the scrap bin at a hardware store)
  • Alligator clip leads
  • Multimeter
  • Electric stove (not gas)
  • Large plastic 2L soda bottle
  • ¼ cup salt
  • Sandpaper & sheet metal shears

Here’s what you need to do:



Download Student Worksheet & Exercises


How does that work? Do you remember learning about the photoelectric effect in Unit 9? This cuprous oxide solar cell ejects electrons when placed in UV light – and sunlight has enough UV light to make this solar cell work. Those free electrons are now free to flow – which is exactly what we’re measuring with the volt meter.


Semiconductors are the secret to making solar cells. A semiconductor is a material that is part conductor, part insulator, meaning that electricity can flow freely and not, depending on how you structure it. There are lots of different kinds of semiconductors, including copper and silicon.


In semiconductors, there’s a gap (called the bandgap) that’s like a giant chasm between the free electrons (electrons knocked out of its shell) and bound electrons (electrons attached to an atom). Electrons can be either free or attached, but it costs a certain amount of energy to go either way (like a toll both).


When sunlight hits the semiconductor material in the solar cell, some of the electrons get enough energy to jump the gap and get knocked out of their shell to become free electrons. The free electrons zip through the material and create a low of electrons. When the sun goes down, there’s no source of energy for electrons to get knocked out of orbit, so they stay put until sunrise.


Does it really matter what angle the solar cell makes with the incoming sunlight? If so, does it matter much? When the sun moves across the sky, solar cells on a house receive different amounts of sunlight. You’re going to find out exactly how much this varies by building your own solar vehicles.


Exercises Answer the questions below:


  1. The sunlight causes the electrons to flow from the cuprous oxide because of:
    1. Photosynthesis
    2. The electromagnetic spectrum
    3. The photoelectric effect
    4. The photochemical principle
  2. What material do most solar cells use instead of copper?
  1. What part of the electromagnetic spectrum is most active in this experiment?
    1. Visible Light
    2. Ultraviolet Light
    3. Gamma Rays
    4. Microwaves
  2. When you read amps, you read:
    1. Current
    2. Voltage
    3. Power Draw
    4. Work

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Stirling Engine

Saturday May 1, 2010

This project is for advanced students.This Stirling Engine project is a very advanced project that requires skill, patience, and troubleshooting persistence in order to work right.  Find yourself a seasoned Do-It-Yourself type of adult (someone who loves to fix things or tinker in the garage) before you start working on this project,  or you’ll go crazy with nit-picky things that will keep the engine from operating correctly.  This makes an excellent project for a weekend.


Developed in 1810s, this engine was widely used because it was quiet and could use almost anything as a heat source. This kind of heat engine squishes and expands air to do mechanical work. There’s a heat source (the candle) that adds energy to your system, and the result is your shaft spins (CD).


This engine converts the expansion and compression of gases into something that moves (the piston) and rotates (the crankshaft). Your car engine uses internal combustion to generate the expansion and compression cycles, whereas this heat engine has an external heat source.


This experiment is great for chemistry students learning about Charles’s Law, which is also known as the Law of Volumes, which describes how gases tend to expand when they are heated and can be mathematically written like this:



where V = volume, and T = temperature. So as temperature increases, volume also increases. In the experiment you’re about to do, you will see how heating the air causes the diaphragm to expand which turns the crank.


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Here’s what you need:


  • three soda cans
  • old inner tube from a bike wheel
  • super glue and instrant dry
  • electrical wire (3- conductor solid wire)
  • 3 old CDs
  • one balloon
  • penny
  • nylon bushing (from hardware store)
  • alcohol burner (you can build one out of soda cans or Sterno canned heat)
  • fishing line (15lb. test or similar)
  • pack of steel wool
  • drill with 1/16″ bit
  • pliers
  • scissors
  • razor
  • wire cutters
  • electrical tape
  • push pin
  • permanent marker
  • Swiss army knife (with can opener option)
  • template
  • HINT: The “circle template” mentioned at 21:57 is actually just a circle traced from the bottom of the soda can onto a sheet of paper

The Stirling heat engine is very different from the engine in your car.  When Robert Stirling invented the first Stirling engine in 1816, he thought it would be much more efficient than a gasoline or diesel engine. However, these heat engines are used only where quiet engines are required, such as in submarines or in generators for sailboats.



Download Student Worksheet & Exercises


Here’s how a Stirling engine is different from the internal-combustion engine inside your car. For example, the gases inside a Stirling engine never leave the engine because it’s an external combustion engine. This heat engine does not have exhaust valves as there are no explosions taking place, which is why Stirling engines are quieter. They use heat sources that are outside the engine, which opens up a wide range of possibilities from candles to solar energy to gasoline to the heat from your hand.


There are lots of different styles of Stirling engines. In this project, we’ll learn about the Stirling cycle and see how to build a simple heat engine out of soda cans.  The main idea behind the Stirling engine is that a certain volume of gas remains inside the engine and gets heated and cooled, causing the crankshaft to turn. The gases never leave the container (remember – no exhaust valves!), so the gas is constantly changing temperature and pressure to do useful work.  When the pressure increases, the temperature also increases. And when the temperature of the gases decreases, the pressure also goes down. (How pressure and temperature are linked together is called the “Ideal Gas Law”.)


Some Stirling engines have two pistons where one is heated by an external heat source like a candle and the other is cooled by external cooling like ice. Other displacer-type Stirling engines has one piston and a displacer. The displacer controls when the gas is heated and cooled.


In order to work, the heat engine needs a temperature difference between the top and bottom of the cylinder. Some Stirling engines are so sensitive that you can simply use the temperature difference between the air around you and the heat from your hand. Our Stirling engine uses temperature difference between the heat from a candle and ice water.


The balloon at the top of the soda can is actually the ‘power piston’ and is sealed to the can.  It bulges up as the gas expands. The displacer is the steel wool in the engine which controls the temperature of the air and allows air to move between the heated and cooled sections of the engine.


When the displacer is near the top of the cylinder, most of the gas inside the engine is heated by the heat source and gas expands (the pressure  builds inside the engine, forcing the balloon piston up). When the displacer is near the bottom of the cylinder, most of the gas inside the engine cools and contracts. (the pressure decreases and the balloon piston is allowed to contract).


Since the heat engine only makes power during the first part of the cycle, there’s only two ways to increase the power output: you can either increase the temperature of the gas (by using a hotter heat source), or by cooling the gases further by removing more heat (using something colder than ice).


Since the heat source is outside the cylinder, there’s a delay for the engine to respond to an increase or decrease in the heat or cooling source. If you use only water to cool your heat engine and suddenly pop an ice cube in the water, you’ll notice that it takes five to fifteen seconds to increase speed. The reason is because it takes time for the additional heat (or removal of heat by cooling) to make it through the cylinder walls and into the gas inside the engine. So Stirling engines can’t change the power output quickly. This would be a problem when getting on the freeway!


In recent years, scientists have looked to this engine again as a possibility, as gas and oil prices rise, and exhaust and pollutants are a concern for the environment. Since you can use nearly any heat source, it’s easy to pick one that has a low-fume output to power this engine. Scientists and engineers are working on a model that uses a Stirling engine in conjunction with an internal-combustion engine in a hybrid vehicle… maybe we’ll see these on the road someday!


Exercises


  1. What is the primary input of energy for the Stirling engine?
  2.  As Pressure increases in a gas, what happens to temperature?
    1. It increases
    2. Nothing
    3. It decreases
    4. It increases, then decreases
  3. What is the primary output of the Stirling engine?

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Galvanometers

Sunday April 4, 2010

Galvanometers are coils of wire connected to a battery. When current flows through the wire, it creates a magnetic field. Since the wire is bundled up, it multiplies this electromagnetic effect to create a simple electromagnet that you can detect with your compass.
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Here’s what you need to do:


Materials:


  • magnet wire
  • sand paper
  • scissors
  • compass
  • AA battery case
  • 2 AA batteries
  • 2 alligator clip wires


Download Student Worksheet & Exercises


1. Remove the insulation from about an inch of each end of the wire. (Use sandpaper if you’re using magnet wire.)


2. Wrap the wire at least 30-50 times around your fingers, making sure your coil is large enough to slide the compass through.


3. Connect one end of the wire to the battery case wire.


4. While looking at the compass, repeatedly tap the other end of the wire to the battery. You should see the compass react to the tapping.


5. Switch the wires from one terminal of the battery to the other. Now tap again. Do you see a difference in the way the compass moves?


You just made a simple galvanometer. “Oh boy, that’s great! Hey Bob, take a look! I just made a….a what?!?” I thought you might ask that question. A galvanometer is a device that is used to find and measure electric current. “But, it made a compass needle move…isn’t that a magnetic field, not electricity?” Ah, yes, but hold on a minute. What is electric current…moving electrons. What do moving electrons create…a magnetic field! By the galvanometer detecting a change in the magnetic field, it is actually measuring electrical current! So, now that you’ve made one let’s use it!


More experiments with your galvanometer

You will need:


  • Your handy galvanometer
  • The strongest magnet you own
  • Another 2 feet or more of wire
  • Toilet paper or paper towel tube

1. Take your new piece of wire and remove about an inch of insulation from both ends of the wire.


2. Wrap this wire tightly and carefully around the end of the paper towel tube. Do as many wraps as you can while still leaving about 4 inches of wire on both sides of the coil. You may want to put a piece of tape on the coil to keep it from unwinding. Pull the coil from the paper towel tube, keeping the coil tightly wrapped.


3. Hook up your new coil with your galvanometer. One wire of the coil should be connected to one wire of the galvanometer and the other wire should be connected to the other end of the galvanometer.


4. Now move your magnet in and out of the the coil. Can you see the compass move? Does a stronger or weaker magnet make the compass move more? Does it matter how fast you move the magnet in and out of the coil?


Taa Daa!!! Ladies and gentlemen you just made electricity!!!!! You also just recreated one of the most important scientific discoveries of all time. One story about this discovery, goes like this:


A science teacher doing a demonstration for his students (can you see why I like this story) noticed that as he moved a magnet, he caused one of his instruments to register the flow of electricity. He experimented a bit further with this and noticed that a moving magnetic field can actually create electrical current. Thus tying the magnetism and the electricity together. Before that, they were seen as two completely different phenomena!


Now we know, that you can’t have an electric field without a magnetic field. You also cannot have a moving magnetic field, without causing electricity in objects that electrons can move in (like wires). Moving electrons create a magnetic field and moving magnetic fields can create electric currents.


“So, if I just made electricity, can I power a light bulb by moving a magnet around?” Yes, if you moved that magnet back and forth fast enough you could power a light bulb. However, by fast enough, I mean like 1000 times a second or more! If you had a stronger magnet, or many more coils in your wire, then you could make a greater amount of electricity each time you moved the magnet through the wire.


Believe it or not, most of the electricity you use comes from moving magnets around coils of wire! Electrical power plants either spin HUGE coils of wire around very powerful magnets or they spin very powerful magnets around HUGE coils of wire. The electricity to power your computer, your lights, your air conditioning, your radio or whatever, comes from spinning magnets or wires!


“But what about all those nuclear and coal power plants I hear about all the time?” Good question. Do you know what that nuclear and coal stuff does? It gets really hot. When it gets really hot, it boils water. When it boils water, it makes steam and do you know what the steam does? It causes giant wheels to turn. Guess what’s on those giant wheels. That’s right, a huge coil of wire or very powerful magnets! Coal and nuclear energy basically do little more than boil water. With the exception of solar energy almost all electrical production comes from something huge spinning really fast!


Exercises


  1. Why didn’t the coil of wire work when it wasn’t hooked up to a battery? What does the battery do to the coil of wire?
  2. How does a moving magnet make electricity?
  3. What makes the compass needle deflect in the second coil?
  4. Does a stronger or weaker magnet make the compass move more?
  5. Does it matter how fast you move the magnet in and out of the coil?

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Which way is North?

Sunday April 4, 2010

I can still remember in 2nd grade science class wondering about this idea. And I still remember how baffled my teacher was when I asked her this question: “Doesn’t the north tip of a compass needle point to the south pole?” Think about this – if you hold up a magnet by a string, just like the needle of a compass, does the north end of the magnet line up with the north or south pole of the earth?


If you remember about magnets, you know that opposite attract. So the north tip of the compass will line up with the Earth’s SOUTH pole. So compasses are upside-down! Here’s an activity you can do right now…
Materials:


  • magnet
  • compass
  • string

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Download Student Worksheet & Exercises


The magnetic pole which was attracted to the Earth’s north pole was labeled as the Boreal or “north-seeking pole” in the 1200s, which was later shortened to “north pole”. To add to the confusion, geologists call this pole the North Magnetic Pole.


Exercises


  1. How are the lines of force different for the two magnets?
  2. How far out (in inches measured from the magnet) does the magnet affect the compass?
  3. What makes the compass move around?
  4. Do you think the compass’s north–south indicator is flipped, or the Earth’s North Pole where the South Pole is? How do you know?

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Electromagnet

Sunday April 4, 2010

After you’ve completed the galvanometer experiment, try this one!


You can wrap wire around an iron core (like a nail), which will intensify the effect and magnetize the nail enough for you to pick up paperclips when it’s hooked up. See how many you can lift!


You can wrap the wire around your nail using a drill or by hand. In the picture to the left, there are two things wrong: you need way more wire than they have wrapped around that nail, and it does not need to be neat and tidy. So grab your spool and wrap as much as you can – the more turns you have around the nail, the stronger the magnet.


(We included this picture because there are so many like this in text books, and it’s quite misleading! This image is supposed to represent the thing you’re going to build, not be an actual photo of the finished product.)


Find these materials:


  • Batteries in a battery holder with alligator clip wires
  • A nail that can be picked up by a magnet
  • At least 3 feet of insulated wire (magnet wire works best but others will work okay)
  • Paper Clips
  • Masking Tape
  • Compass

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1. Take your wire and remove about an inch of insulation from both ends. (Use sandpaper if you’re using magnet wire.)


2. Wrap your wire many, many times around the nail. The more times you wrap the wire, the stronger the electromagnet will be. Be sure to always wrap in the same direction. If you start wrapping clockwise, for example, be sure to keep wrapping clockwise.


3. Now connect one end of your wire to one terminal of the battery using an alligator clip (just like we did in the circuits from Unit 10).


4. Lastly, connect the other end of the wire to the other terminal of the battery using a second alligator clip lead to connect the electromagnet wire to the battery wire. This is where the wire may begin to heat up, so be careful.


5. Move your compass around your electromagnet. Does it affect the compass?


6. See if your electromagnet can pick up paper clips.


7. Switch the wires from one terminal of the battery to the other. Electricity is now moving in the opposite direction from the direction it was moving in before. Try the compass again. Do you see a change in which end of the nail the north side of the compass points to?


What happened there? By hooking that coil of wire up to the battery, you created an electromagnet. Remember, that moving electrons causes a magnetic field. Well, by connecting the two ends of your wire up to the battery, you caused the electrons in the wire to move through the wire in one direction.


Since many electrons are moving in one direction, you get a magnetic field! The nail helps to focus the field and strengthen it. In fact, if you could see the atoms inside the nail, you would be able to see them turn to align themselves with the magnetic field created by the electrons moving through the wire. You might want to test the nail by itself now that you’ve done the experiment. You may have caused it to become a permanent magnet!
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