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

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

Here’s what you need:

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

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

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

2. Put a car on the track.

3. Let the car go.

4. Mark or measure how far it went.

Download Student Worksheet & Exercises

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

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

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

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

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

Exercises

1. Where is the potential energy greatest?
2. Where is the kinetic energy greatest?
3. Where is potential energy lowest?
4. Where is kinetic energy lowest?
5. Where is KE increasing, and PE is decreasing?
6. Where is PE increasing and KE decreasing?

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

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

Here’s what you need:

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

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

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

Download Student Worksheet & Exercises

Tips & Tricks

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

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

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

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

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

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

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

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

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

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

“Where did it fly off?”

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

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

Exercises 

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

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

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

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

Here’s what you need:

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

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

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

 
Download Student Worksheet & Exercises

Exercises Answer the questions below:

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

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

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

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Advanced students: Download your P-Shooter Lab here.

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

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

Here’s what you need:

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

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

Here are instructions for making your own height-gauge:

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

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

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

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

Now, let’s calculate the potential energy:

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

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

mgh = 0.5 mv² gives v = (2gh)^1/2

Plug in your numbers to get:

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

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

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

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

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

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

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

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Here’s what you need:

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

 
Download Student Worksheet & Exercises

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

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

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

Want to make a more advanced catapult? 

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

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

Materials:

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

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

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

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

Exercises Answer the questions below:

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

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

For these experiments, find your materials:

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

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Here’s what you do:

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

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

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

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

Download Student Worksheet & Exercises

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

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

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

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

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

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

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

Chaos Pendulum

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

Exercises

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

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

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Materials: a rubber band

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

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

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

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

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We’re going to experiment with Newton’s Third law by blowing up balloons and letting them rocket, race, and zoom all over the place. When you first blow up a balloon, you’re pressurizing the inside of the balloon by adding more air (from your lungs) into the balloon. Because the balloon is made of stretchy rubber (like a rubber band), the balloon wants to snap back into the smallest shape possible as soon as it gets the chance (which usually happens when the air escapes through the nozzle area). And you know what happens next – the air inside the balloon flows in one direction while the balloon zips off in the other.

Question: why does the balloon race all over the room? The answer is because of something called ‘thrust vectoring’, which means you can change the course of the balloon by angling the nozzle around. Think of the kick you’d feel if you tried to angle around a fire hose operating at full blast. That kick is what propels balloons and fighter aircraft into their aerobatic tricks.

We’re going to perform several experiments here, each time watching what’s happening so you get the feel for the Third Law. You will need to find:

• balloons
• string
• wood skewer
• two straws
• four caps (like the tops of milk jugs, film canisters, or anything else round and plastic about the size of a quarter)
• wooden clothespin
• a piece of stiff cardboard (or four popsicle sticks)
• hot glue gun

First, let’s experiment with the balloon. Here’s what you can do:

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1. Blow up the balloon (don’t tie it)

2. Let it go.

3. Wheeeee!

4. Tie one end of the string to a chair.

5. Blow up the balloon (don’t tie it).

6. Tape a straw to it so that one end of the straw is at the front of the balloon and the other is at the nozzle of the balloon.

7. Thread the string through the straw and pull the string tight across your room.

8. Let go. With a little bit of work (unless you got it the first time) you should be able to get the balloon to shoot about ten feet along the string.

This is a great demonstration of Newton’s Third Law – the air inside the balloon shoots one direction, and the balloon rockets in the opposite direction. It’s also a good opportunity to bring up some science history. Many folks used to believe that it would be impossible for something to go to the moon because once something got into space there would be no air for the rocket engine to push against and so the rocket could not “push” itself forward.

In other words, those folks would have said that a balloon shoots along the string because the air coming out of the balloon pushes against the air in the room. The balloon gets pushed forward. You now know that that’s silly! What makes the balloon move forward is the mere action of the air moving backward. Every action has an equal and opposite reaction.

Multi-Stage Balloon Rocket

You can create a multi-stage balloon rocket by adding a second balloon to the first just like you see here in the video:

Tie a length of string through the room, having at least twenty feet of clear length.  Thread two straws onto the string before securing the end.  Punch the bottoms out of two foam coffee cups and tape parallel to the threaded straws.

Blow up balloons while they are inside the cups, so they extend out either end.  When blowing up the second balloon, sandwich the untied end of the first inflated balloon between the second inflated balloon surface and inside the cup.  Hold the second balloon’s end with a clothespin and release!

Balloon Racecar

Now let’s use this information to create a balloon-powered racecar. You’ll need the rest of the items outlined above to build your racecar. NOTE: in the video, we’re using the popsicle sticks, but you can easily substitute in a sheet of stiff cardboard for the popsicle sticks. (Either one works great!)

 
Download Student Worksheet & Exercises

You now have a great grasp of Newton’s three laws and with it you understand a good deal about the way matter moves about on Earth and in space. Take a look around. Everything that moves or is moved follows Newton’s Laws.

In the next unit, we will get into Newton’s Third Law a little deeper when we discuss momentum and conservation of momentum by whacking things together *HARD*. But more on this later…

Exercises

1. What is Newton’s Third Law of Motion?
2. Why does the balloon stop along the string?

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Advanced students: Download your Balloon Racer Lab here.

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A common misconception in science is that centrifugal and centripetal force (or acceleration) are the same thing. These two terms constantly throw students into frenzy, mostly because there is no clear definition in most textbooks. Here’s the scoop: centripetal and centrifugal force are NOT the same thing!

This experiment is mostly for Advanced Students, but here’s a quick lesson you can do with your younger students…

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Before we jump in, let’s recap what we’ve learned so far. A ball sitting still has a position you can chart on a map (latitude, longitude, and altitude), but no velocity or acceleration, because it’s not moving. When you kick the ball, that’s when it gets interesting. The second your toe touches the ball, things start to change. Velocity is a change of position. If you kick the ball ten feet, and it takes five seconds to go the distance, the average speed of the ball is 2 feet per second (about 1.4 MPH).

The trickier part of this scenario has to do with acceleration, which is the change in velocity. When you drive on the freeway at a constant 65 MPH, your acceleration is zero. Your speed does not change, so you have no acceleration. Your position is constantly changing, but you have constant speed. For example, when you enter the freeway, your speed changes from zero to 65 MPH in, say, ten seconds. Your acceleration is greatest when your foot first hits the gas – when your speed changes the most – when you’re moving from zero to a higher speed.

There’s an interesting effect that happens when you travel in a curve. You can feel the effect of a different type of acceleration when you suddenly turn your car to the right – you will feel a push to the left. If you are going fast enough and you take the turn hard enough, you can get slammed against the door. So – who pushed you?

Think back to the first law of motion. An object in motion tends to stay in motion unless acted upon by an external force. This is the amazing part – the car is the external force. Your body was the object in motion, wanting to stay in motion in a straight line. The car turns, and your body still tries to maintain its straight path, but the car itself gets in the way. When you slam into the car door, the car is turning itself into your path, forcing you to change direction.

This effect is true when you travel in a car or in a roller coaster. It’s the reason the water stays in the bucket when you swing it over your head. Physical motion is everywhere, challenging toddlers learning to walk as well as Olympic downhill skiers to go the distance. Here’s a quick experiment you can do right now to wrap your head around this idea:

Here’s what you need to find for these experiments:

• bucket
• water
• outdoor area
• you
• clear tubing (about 12-18″ long)
• nylon or metal barbed union that fits inside the tubing
• empty soda bottle
• clean wine cork
• string

Bucket Splash

Fill a bucket half-full with water. Grasp the handle and swing it over your head in a circle in the vertical direction. Try spinning around while holding the handle out in front of your chest to swing it in the horizontal plane. Vary your spin speed to find the minimum!

Now let’s take a deeper look at centripetal, centrifugal, and how you can measure the g-force when taking a sharp turn in your car:

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For Advanced Students:

Centripetal (translation = “center-seeking” ) is the force needed to keep an object following a curved path. Remember how objects will travel in a straight line unless they bump into something or have another force acting on it (gravity, drag force, etc.)? Well, to keep the bucket of water swinging in a curved arc, the centripetal force can be felt in the tension experienced by the handle (or your arm, in our case). Swinging an object around on a string will cause the rope to undergo tension (centripetal force), and if your rope isn’t strong enough, it will snap and break, sending the mass flying off in a tangent (straight) line until gravity and drag force pull the object to a stop. This force is proportional to the square of the speed – the faster you swing the object, the higher the force.

Centrifugal (translation = “center-fleeing”) force has two different definitions, which also causes confusion. The inertial centrifugal force is the most widely referred to, and is purely mathematical, having to do with calculating kinetic forces using reference frames, and is used with Newton’s laws of motion. It’s often referred to as the ‘fictitious force’.

Reactive centrifugal force happens when objects move in a curved path. This force is actually the same magnitude as centripetal force, but in the opposite direction, and you can think of it as the reaction force to the centripetal force. Think of how you stand on the Earth… your weight pushes down on the Earth, and a reaction force (called the “normal” force) pushes up in reaction to your weight, keeping you from falling to the center of the Earth. A centrifugal governor (spinning masses that regulate the speed of an engine) and a centrifugal clutch (spinning disk with two masses separated by a spring inside) are examples of this kind of force in action.

Say WHAT?!?

Don’t worry if these ideas make your brain turn into a pretzel. Most college students take three courses in this before it makes sense to them. Here’s one more example: imagine driving a car along a banked turn. The road exerts a centripetal force on the car, keeping the car moving in a curved path (the “banked” turn). If you neglected to buckle your seat belt and the seats have a fresh coat of Armor-All (making them slippery), then as the car turns along the banked curve, you get “shoved” toward the door. But who pushed you? No one – your body wanted to continue in a straight line but the car keeps moving in your path, turning your body in a curve. The push of your weight on the door is the reactive centrifugal force, and the car pushing on you is the centripetal force.

What about the fictitious (inertial) centrifugal force? Well, if you imagine being inside the car as it is banking with the windows blacked out, you suddenly feel a magical ‘push’ toward the door away from the center of the bend. This “push” is the fictitious force invoked because the car’s motion and acceleration is hidden from you (the observer) in the reference frame moving within the car.

Okay, enough talk for now. Let’s make two acceleration-measuring instruments (called ‘accelerometers’) so you can jump, run, swing, and zoom around to find out how many g’s you can pull. You’re going to make a cork-accelerometer and a g-force ring, both of which are used by my students when I teach mechanical engineering dynamics.

Cork Accelerometer

Fill an empty soda bottle to the top with water. Modify the soda bottle cap as follows: attach a string 8-10″ long to a clean wine cork. Hot glue the free end of the string to the inside of the cap. Place the cork and string inside the bottle and screw on the top (try to eliminate the air bubbles). The cork should be free to bob around when you hold the bottle upside-down.

 
Download Student Worksheet & Exercises

To use the accelerometer: invert the bottle and try to make the cork move about. Remember – it is measuring acceleration, which is the change in speed. It will only move when your speed changes. You can do this experiment in a car while doing your other vehicle experiment: Why Bother With Seatbelts?. The trouble with this accelerometer is that there are no measurements you can take – it’s purely visual. This next activity is more accurate at measuring the number of g-s you pull in a sharp turn (whether in a vehicle or in a roller coaster!)

G-Force Ring Accelerometer

One more university-level gadget for demonstrating the fascinating world of physical dynamics. This quick homemade device roughly measures acceleration in “g’s”. We used it to measure the g-force on roller coasters at Six Flags Magic Mountain, and it worked just as well as the expensive ones you buy in scientific catalogs!

Get about a foot of tubing – the bigger the diameter, the easier it will be to read. Also get a barbed union (plastic barbs work just fine). Fill your tube halfway with COLORED water (it’s impossible to read when it’s clear). Blue, green, red… your choice of food dye additive. Make an O-shape using your barb to water-seal the junction. Grab hold of one side and hold the circle vertical, with the barb-end pointing to the sky. The water should fill the bottom half, and air fills the top half. Make sure there are equal amounts of water and air in your tube. Make a mark on the tube where the water meets the air with a black marker. This is your 0-g reading (relative, of course). No acceleration. Not a whole lot of fun.

Now, for your 1-g mark – measure up 45 degrees from the first mark. (If the top of the circle is 90 degrees, and the 0-g mark is zero degrees, find the halfway point and label it).

The 2-g mark is 22.5 degrees up from the 1-g mark.

3-g mark is 11.25 degrees up from the last mark. And 4-g is 5.6 degrees up from the last mark. (See a pattern? You can prove this mathematically in college, and it’s kind of fun to figure out!)

Now, next time mom drives around town, hold the tube in your hand so that the water line starts at the zero mark. When she pulls a turn, see how far it sloshes up and tell her how many g’s she pulled. We also used to have contests to see who could pull the most g’s while spinning in a circle. Have fun!

Advanced Students:

Advanced Students: Download your G-Force lab here.

Exercises 

1. Which accelerometer was better at giving a visual representation of accelerating?
2. Which one do you prefer? Why?
3. What activity did you do that created the most acceleration?
4. What does that tell you about acceleration?

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Newton’s Second Law is one of the toughest of the laws to understand but it is very powerful. In its mathematical form, it is so simple, it’s elegant. Mathematically it is F=ma or Force = Mass x Acceleration. An easy way to remember that is to think of your mother trying to get you out of bed in the morning. Force equals MA’s coming to get you! (I did mention how bad physics jokes are, right?)

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Newton’s Second Law

In English, Newton’s Second Law can be stated a few different ways:

The more mass something has and/or the faster it’s accelerating, the more force it will put on whatever it hits. F=ma For example, a car colliding at 30 mph will hit a lot harder then a fly colliding at 30 mph.

The more mass something has, the more force that’s needed to get it to accelerate. a=F/m This, by the way, is a mathematical definition for acceleration. For example, it is a lot harder to get a train to accelerate than it is to get a ping pong ball to accelerate.

So force = mass X acceleration. Let’s try a couple of things and see if we can make that make sense.

Now, time to do an experiment. You will need:

• something slightly slanted, like a slanted driveway or a long board (or even a table propped up on one end)
• something to move down the slant, like a toy car or ball
• a stopwatch
• pen and paper

I’m going to assume you’re using the toy car and a driveway. Feel free to modify the experiment for whatever you are using.

1. Take the toy car to the top of the driveway.

2. Let it go.

3. Watch it carefully as it rolls.

4. If you’d like, you can time the car and mark how far it goes every second like we did in this acceleration experiment.

5. If you time it, measure the distances it went each second and write them down.

 
Download Student Worksheet & Exercises

What I’m hoping you will see here is that the car accelerates from zero to a certain velocity but then stays at that velocity as it continues down the driveway. In other words, it reaches its terminal velocity. If you timed and marked the distances you should see that the car goes the same distance each second if it is indeed staying at a constant velocity. If the object you are using to roll down the slant, continues to accelerate down the entire ramp, see if you can find something that has more friction to it (a toy car that doesn’t roll quite to easily, for example).

Ok, so what’s going on? F=ma right? Acceleration can’t happen without force. What two forces are effecting the car? (Imagine the Jeopardy theme song here). If you said gravity and friction, give yourself a handshake. When the car is going at a constant velocity, is it accelerating? Nope, acceleration is a change in speed or direction.

“But you just said two forces are effecting my little car and that force causes acceleration and yet my car is not accelerating. Why not?”

Well, there’s one little thing I haven’t mentioned yet, which is why we did this experiment. In this case, the force of gravity pulling on the car and the force of friction pushing on the car is equal (remember, that’s terminal velocity right?). So the net force on the car is zero. The pulling force is equal to the pushing force so there is zero force on the car. Force is measured in Newton’s (name sounds familiar right?) so imagine that there are 3 Newtons of force pulling on the car due to gravity and 3 Newtons of force pushing on the car due to friction. 3 – 3 = 0. Zero force equals zero acceleration because you need force to have acceleration. By the way, 1 Newton is about the same amount of force that it takes to lift a full glass of milk.

Advanced Students: Download your Downhill Races Lab here.

Exercises 

1. You should notice a difference between these graphs and the ones from the driveway races. What is it? (Hint: look to second half of the graph.)
2.  The first graph doesn’t continue to curve, but straightens out.  What does this mean about the velocity?
3.  in the second graph, the slope flattens out completely, what does this mean about the acceleration?
4.  If the acceleration is zero, what does that mean about the net force?
5.  What are the forces acting on the toy car as it is going down the ramp?
6.  Name 3 other examples

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Gyroscopes defy human intuition, common sense, and even appear to defy gravity. You’ll find them in aircraft navigation instruments, games of Ultimate Frisbee, fast bicycles, street motorcycles, toy yo-yos, and the Hubble Space Telescope. And of course, the toy gyroscope (as shown here). Gyroscopes are used at the university level to demonstrate the principles of angular momentum, which is what we’re going to learn about here.

If you happen to have one of these toy gyroscopes, pull it out and play with it (although it’s not essential to this experiment). Notice that you can do all sorts of things with it when you spin it up, such as balance it on one finger (or even on a tight string). Wrap one end with string and hold the string vertically and you’ll find the gyro slowly rotates about the vertical string instead of flopping downward (as most objects do in Earth’s gravitational field). But why? Here’s the answer in plain English:

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Imagine a spinning bicycle wheel hanging from a rope. Take a freeze-frame image of the wheel in your mind and make the top part of the wheel is at 12 o’clock, the left side at 9 o’clock, the bottom is 6 o’clock, and the center axle pointing toward you. And the wheel was rotating clockwise. Got it?

The 6 o’clock position wants to move to the left. When the 6 o’clock position gets to the 9 o’clock, it still wants to move left.

The original 9 o’clock position wants to move up. When the 9 o’clock position gets to 12 o’clock, it still wants to move up.

The 12 o’clock position wants to move to the right. When the 12 o’clock position moves to the 3 o’clock, it still wants to move right. See the pattern?

Okay, here’s what you want to see now: as the top and bottom (12 and 6 o’clock) positions of the wheel rotate, the forces cancel each other out. Same with the 3 and 9 o’clock positions. And because the wheel is symmetrical, this occurs for every spot on the wheel. When this happens, the bicycle wheel turns (precesses), instead of falling. This is also why a spinning gyroscope will appear to float at the end of the string instead of dangling.

One more piece to the puzzle: the wheel itself is accelerating. Any object that swings in a circle is accelerating, because in order to move in a circle, you need to be constantly changing your direction (or else you’d be off in a straight line tangent to your circular path). When you swing a bag of oranges around your head, or a yo-yo on a string, or even taking a turn in a car, acceleration is happening. We’ll talk more about that when we do our g-force experiments. For right now, let’s get our hands on a super-cool experiment that you usually only see at science museums or inside physics classrooms.

You’ll need to find:

• a bicycle wheel (it needs to be detached from a bicycle – note that the front wheel is pretty easy to detach)
• a piece of rope (about 2-3′)
• and an office chair

1. Carefully hold the bicycle wheel by the axle and give it a spin. Try to get it to spin as fast as you can but be VERY careful to hold onto it tightly and don’t get your fingers in the spokes. It works well if someone else can spin it for you.

2. While it’s spinning try to move it around. You’ll find that the wheel does not want to be moved around and tries to do its own thing when you move it.

3. Take a string and loop it around one side of the axle of the wheel. Spin the wheel fast and let go of the wheel while holding onto the string. The wheel will stay spinning and defy gravity by staying straight up and down. Really! Try it, it’s very cool!

Download Student Worksheet & Exercises

This experiment demonstrates the power of Newton’s Second Law: Force equals mass times acceleration. The mass is the mass of the wheel, in particular, the mass of the tire. The acceleration is the spinning wheel. Remember, acceleration is not just change in speed but also change in direction. Every point on the spinning wheel is constantly changing direction so the wheel is accelerating.

Since acceleration times mass has to equal force, (math says so) the spinning wheel has a force. This force is strong enough to defy gravity and is what you feel when you hold the axles of the wheel and try to move it. This same force is what keeps a top spinning, why footballs are thrown with a spiral, why satellites spin and so on. It’s pretty incredible to think that a force can be created by nothing more than accelerating mass.

Best Physics Joke

A friend once told me of a funny April Fool’s joke played at his office. He worked at a company that fixed aircraft instruments, where they received all sorts of old airplane parts. One day, his office anonymously received an old instrument from a WWII bomber, and the gyro in this thing was HUGE. Then he had an idea – he removed the gyro from the outer instrument casing, fixed it, spun it up (and it would continue spin for hours), and packed it up in his boss’s briefcase. When his boss went to lunch and picked up his briefcase, can you imagine what happened? (Tell me in the comment field below!)

Exercises

1. What did it feel like when you tried to turn the wheel after it was spun?
2. What direction (orientation) does the wheel want to be in?
3. When you were on the spinning chair/platform, which way did you turn?
4. If you turned the wheel left, you should have spun the same way, where is the force coming from the pushed you in that direction?
5. What happened to the wheel while you held on to the string? Did it stay upright, or dangle?
6. Why do you think it stayed upright?

For Advanced Students:

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When you grab hold of the axle of a spinning bicycle wheel, you feel a ‘push’ in an odd direction. This ‘push’ is called precession and is a wobble from the spin axis because you tried to move it in a direction it doesn’t want to go.

Precession happens when you grab a spinning object at its rotating axis (like the ends of the gyroscope or the axle of a bicycle wheel) and try to move it about. You’ll find a fierce resistance crop up. That’s precession. The question is why? Why does the gyro act like this?

Normally, this area of scientific study is enough to make most 3rd year engineering students cry. The engineering required to model this system are complex, let alone finding the solution to the mathematical differential equations that make up the model itself. So we’re not going to get into the nit-picky stuff, but instead talk about how it actually works using plain English. Here’s what’s going on:

Most gyroscopes are designed to have most of the rotating mass far away from the center axis (think of a thin disk with a heavy rim, like a bike wheel) so it can resist motion in certain directions. A spinning bike wheel stores large amounts of energy. Remember Newton’s first law of motion? (An object in motion tends to stay in motion unless something else interferes.) Any time you try to torque the bike axle, the wheel will try to ‘compensate’ for this and push in a different direction. (Parts of a car engine will also do this – think of the fast-spinning shaft or fan when you try to take a sharp turn.)

Who first thought up this stuff?

German scientist Johann Bohnenberger built the first gyroscope as a giant spinning ball near the start of the 1800s. About two decades later, Walter R. Johnson (an American) shifted the spinning solid sphere into a spinning disc, which was later upgraded to describing the Earth’s rotation by a French mathematician Pierre-Simon Laplace. Léon Foucault attempted to use the gyroscope in experiments that could detect the earth’s rotation (while still being on the planet itself), but his work lacked a frictionless mount (which was later developed), and now the famous Foucault Pendulum is in many science museums across the country. (It’s the one with the 3-story tall, 300-pound brass plumb-bob that knocks over dominoes every 6-14 minutes.)

The first industrial application for the gyroscope was for the military (marine applications, then quickly followed for aircraft) in the early 1900s, followed shortly after by the toy industry. Today gyroscopes are used mostly in navigational systems and inertial guidance systems for ballistic missiles.

You can think of the Earth as a gyro as well. Of precession is the ‘wobble’ a spinning gyro makes when a force is applied (the force in this case is the pull mostly from the sun), then the Earth ‘wobbles’ through one precession cycle about every 26,000 years. What does this mean? It means that the axial poles of the earth are scribing small, slow circles over time (the ‘wobble’). It also means that star positions will slowly change on our gridmarked area of the sky, so every so often we’ll need to update our coordinate systems so we can accurately locate the positions of the stars. (But it’s only a shift of about 1 degree very 70+ years.)

The interesting thing is that the Earth’s precession was actually discovered ages ago by the ancient Greek astronomer Hipparchus (150 B.C.), but it couldn’t be mathematically described until we had Newtonian physics to guide the way (and even then we had a few issues). For example, we had to figure out that the Earth is really not a sphere but more of an ‘squashed sphere’ (imagine squashing a ball of clay slightly between your fingers so that the middle bulges out). And both the Sun and the Moon pull on the bulge (lunisolar precession), which adds more to the ‘wobble’ of the Earth. And did I mention the Sun is not a perfect sphere, either? (It’s actually kind of flat… so that had to be accounted for as well.)

All of this can be mathematically modeled in the world of engineering through a conservation law called Angular Momentum. For those of you who really want to learn more about angular momentum (which is purely your choice, but it is out of the scope of this program because it’s a college-level topic), click here to download a chapter from an advanced textbook.

Advanced students: Download your Gyro Wheel Lab here.

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This experiment is one of my favorites in this acceleration series, because it clearly shows you what acceleration looks like.

The materials you need is are:

• a hard, smooth ball (a golf ball, racket ball, pool ball, soccer ball, etc.)
• tape or chalk
• a slightly sloping driveway (you can also use a board for a ramp that’s propped up on one end)

For advanced students, you will also need: a timer or stopwatch, pencil, paper, measuring tape or yard stick, and this printout.

Grab a friend to help you out with this experiment – it’s a lot easier with two people.

Are you ready to get started really discovering what acceleration is all about?

Here’s what you do:
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1. Place the board on the books or whatever you use to make the board a slight ramp. You really don’t want it to be slanted very high. Only an inch or less would be fine. If you wish, you can increase the slant later just to play with it.

2. Put a line across the board where you will always start the ball. Some folks call this the “starting line.”

3. Start the timer and let the ball go from the starting line at the same exact time.

4. Now, this is the tricky part. When the timer hits one second, mark where the ball is at that point. Do this several times. It takes a while to get the hang of this. I find it easiest to have another person do the timing while I follow the ball with my finger. When the person says to stop, I stop my finger and mark the board at that point.

5. Do the exact same thing but this time, instead of marking the place where the ball is at one second, mark where it is at the end of two seconds.

6. Do it again but this time mark it at 3 seconds.

7. Continue marking until you run out of board or driveway.

Download Student Worksheet & Exercises

Take a look at your marks. See how they get farther and farther apart as the ball continues to accelerate? Your ball was constantly increasing speed and as such, it was constantly accelerating. By the way, would it have mattered what the mass of the ball was that you used? No. Gravity accelerates all things equally. This fact is what Galileo was proving when he did this experiment. The the weight of the ball doesn’t matter but the size of the ball might. If you used a small ball and a large ball you would probably see differences due to friction and rotational inertia. The bigger the ball, the more slowly it begins rolling. The mass of the ball, however, does not matter.

Exercises

1. Was the line a straight line?
2. It should be close now, and the slope represents the acceleration it experienced going down the ramp. Calculate the slope of this line.
3. What do you think would happen if you increased the height of the ramp?
4. Knowing what you do about gravity, what is the highest acceleration it can reach?

For Advanced Students…

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Now if you want to whip out your calculators you can find out how fast your ball was accelerating. Take your measuring tape and measure the distance from the starting line to the line you made for the distance the ball traveled in one second.

Let’s say for example that my ball went 6 inches in that first second. Dust off those old formulas and lets play with d=1/2gt² where d is distance, g is acceleration due to gravity and t is time.

We can’t use g here because the object is not in free fall, so instead of g let’s call it “a” for acceleration. Gravity is the force pulling on our ball but due to the slope, the ball is falling at some acceleration less then 32 ft/s².

In this case, d is 6 inches, t is 1 second and a is our unknown.

With a little math we see:

a = 12in/sec² (So our acceleration for our ramp is 12 in/sec² or we could say 1ft/s².)

With a little more math we can see how far our ball should have traveled for each time trial that we did. For one second we see that our ball should have traveled d=1/2 12(12) or d= 6 inches (we knew that one already didn’t we?).

For two seconds we can expect to see that d=1/2 12(22) or d=24 inches.
For three seconds we expect d=1/2 12(32) or d= 54 inches.

Do you see why we need a pretty long board for this?

Now roll the ball down the ramp and actually measure the distance it travels after two and three seconds. Do your calculations match your results? Probably not. Our nasty little friend friction has a sneaky way of messing up results. You should definitely see the distance the ball travels get greater with each second however. So make yourself a table or use one of ours to record your data and jot down your calculations and chart your results like a real scientist.

Advanced students: Download your Driveway Races Lab here.

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If you jump out of an airplane, how fast would you fall? What’s the greatest speed you would reach? Let’s practice figuring it out without jumping out of a plane.

This experiment will help you get the concept of velocity by allowing you to measure the rate of fall of several objects. It’s also a great experiment to record in your science journal.

First, you’ll need to find your materials:

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• stop watch
• feathers (or small pieces of paper, plastic bag or anything light and fluffy)
• a tape measure
• If you’re crunching numbers, you’ll also need a calculator.

Now here’s how to do the experiment:

1. Get 5 or so different light and fluffy objects. Feathers of different size, small strips of paper, parts of a plastic bag, cotton balls, whatever is handy.

2. Make a prediction by writing down the objects you chose in order of how fast you think they will fall. The fastest on top, the slowest on the bottom. Leave space to the right of your prediction so that you can write in your conclusions and then compare the two.

3. Make a table with two columns. Use one column to fill in the name of the items. Use the second column to write down the time it took each object to fall.

4. Drop the different items and time them from the moment you let go to the moment they hit the ground. Be sure to drop each item from about the same height. The higher the better. Just be sure not to fall off anything! We don’t want to measure your velocity!! You might want to drop them two or three times to get an average time.

5. Now compare the items. Which one fell the least amount of time (dropped the fastest)? Which one fell the most amount of time (dropped the slowest)? Write your results next to your hypothesis. By the way, did you find anything that dropped slower than a feather? I have seen very few things that take longer to fall straight down than a feather.

 
Download Student Worksheet & Exercises

Did you see how many of your objects stopped accelerating very quickly? In other words, they reached their terminal velocity soon after you let them go and they fell all the way to the ground at that same constant velocity. This is why a parachute is a sky-diver’s best friend! A human has a decent amount of air resistance but he or she can reach a lethal dose of velocity (120 mph) if dropped from a great height. The parachute increases the air resistance so that the terminal velocity of that sky-diver is quite a bit safer!

Exercises

1. What is velocity?
2. How do acceleration and deceleration relate to velocity?
3. How do we know when an object has reached terminal velocity?

Taking it Further for advanced students:

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We can do a little math here and figure out the actual velocity of your objects. Here’s how to do it:

Measure the height from which you dropped each object. Now take the height of the drop and divide that by the number of seconds it took for it to drop that distance. That’s the velocity of that object. For example, My “from-under-the-couch-six-month-old-dust-bunny” took 3 seconds to fall 6 feet. I take 6 feet and divide it by 3 seconds to get 2 feet/second.

The velocity of my dust bunny is 2 feet/second downward.

Remember, that velocity has a directional component as well as a number. Add a little more math, and I can predict how long my dust bunny will take to fall 15 feet. Take the distance (15 feet) and divide it by the velocity (2 feet/second) and I get 7.5 seconds. It will take my dust bunny 7.5 seconds to fall 15 feet. Hmmm, maybe we should call it a dust snail.

Have you noticed something here? In this experiment, we used a different formula to find out how far something would fall over a given time.

What’s going on? In Unit 1, we ignored their terminal velocity. Those things were in free fall and accelerating (gaining velocity) all the way to the ground. They were never going the same velocity for the entire trip. So, we needed to use the gravitational constant 32 ft/s² in the equation d=1/2 gt² to determine how far something fell in a given amount of time.

For this unit, we are dealing with things that are at an almost constant velocity, (since they reach their terminal velocity quickly) so we can use the much simpler equation d=vt (d is distance, v is velocity and t is time). In the problems we’ve done in this lesson plan, we have modified that formula to find how long the fall took so we’ve used t=d/v.

If you’d like to solve for v you would use v=d/t. Isn’t algebra fun?

Advanced students: Download your terminal velocity lab here.

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Ever wonder how magicians work their magic? This experiment is worthy of the stage with a little bit of practice on your end.

Here’s how this activity is laid out: First, watch the video below. Next, try it on your own. Make sure to send us your photos of your inventions here!

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For this incredibly easy, super-amazing experiment, you’ll need to find:

• a plastic cup
• hard covered book
• toilet paper tube
• a ball that’s a bit smaller then the opening of the cup but larger than the opening of the toilet paper tube (you can also use an egg when you really get good at this trick!)

1. Put the cup on a table.

2. Put the book on top of the cup.

3. This is the tricky part. Put the toilet paper tube upright on the book, exactly over the cup.

4. Now put the ball on top of the toilet paper tube.

5. Check again to make sure the tube and the ball are exactly over the top of the cup.

6. Now, hit the book on the side so that it moves parallel to the table. You want the book to slide quickly between the cup and the tube.

7. If it works right, the book and the tube fly in the direction you hit the book. The ball however falls straight down and into the cup.

8. If it works say TAAA DAAA!

 
Download Student Worksheet & Exercises

This experiment is all about inertia. The force of your hand got the book moving. The friction between the book and the tube (since the tube is light it has little inertia and moves easily) causes the tube to move. The ball, which has a decent amount of weight, and as such a decent amount of inertia, is not effected much by the moving tube. The ball, thanks to gravity, falls straight down and, hopefully, into the cup. Remember the old magician’s trick of pulling the table cloth and leaving everything on the table? Now you know how it’s done. “Abra Inertia”!

So inertia is how hard it is to get an object to change its motion, and Newton’s First Law basically states that things don’t want to change their motion. Get the connection?

Exercises 

1. What are two different pairs of forces in this experiment?
2. Explain where Newton’s Three Laws of motion are observed in this experiment.

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Next time you watch a drag race, notice the wheels. Are they solid metal discs, or do they have holes drilled through the rims? I came up with this somewhat silly, but incredibly powerful quick science demonstration to show my 2nd year university students how one set of rims could really make a difference on the racetrack (with all other things being equal).

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Here’s what you need: two unopened cans of soup.

One should be clam chowder, the other chicken broth. Prop up a long table up on one end about 6-12″ (you can experiment with the height later). You’re going to roll them both down the table at the same time. Which do you expect to reach to bottom first – the chicken or the clam?

Not only do my college students need to figure out which one will win, they also have to tell me why. The secret is in how you calculate the inertia of each. Take a guess, then watch the video, do the activity, then read the explanation at the bottom (in that order) to get the most out of this experiment.

 
Download Student Worksheet & Exercises

Inertia & History

Inertia is a quality of an object that determines how difficult it is to get that object to move, to stop moving, or to change directions. Generally, the heavier an object is, the more inertia it has. An elephant has more inertia than a mushroom. A sumo wrestler has more inertia than a baby. Inertia is made from the Latin word “inert,” which means “lacking the ability to move”. Inertia isn’t something people have a grasp of, though, as it’s something you must mathematically calculate from an object’s mass and size.

When riding in a wagon that suddenly stops, you go flying out. Why? Because an object in motion tends to stay in motion unless acted upon by an outside force (Newton’s First Law). When you hit the pavement, your motion is stopped by the sidewalk (external force). Seatbelts in a car are designed to keep you in place and counteract inertia if the car suddenly stops.

Did you know that Newton had help figuring out this First Law? Galileo rolled bronze balls down an wood ramp and recorded how far each rolled during a one-second interval to discover gravitational acceleration. And René Descartes (the great French philosopher) proposed three laws of nature, all of which Newton studied and use in his published work.

All of these thinkers (and many more) had to overcome the long-standing publicly-accepted theories that stemmed from the Greek philosopher Aristotle, which was no small feat in those days. Aristotle had completely rejected the idea of inertia (he also thought that weight affected falling objects, which we now know to be false). But remember that back then, people argued and talked about ideas rather than performing actual experiments to discover the truth about nature. They used words and reason to navigate through their world more than scientific experimentation.

Who wins, and why?

The chicken soup wins, for a very simple reason. Imagine that the cans are transparent, so you can see what does on inside the cans as they roll down the ramp. Which one has just the can rolling down the ramp, and which has the entire contents locked together as it rolls? The can of the chicken soup will rotate around the soup itself, while the clam chowder acts as a solid cylinder and rotates together. So the inertial mass of the clam is much greater than the inertial mass of the soup, even though the cans weigh the same.

Exercises

1. What is inertia (in your own words)?
2. Why does one soup can always win?

For Advanced Students…

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So, how do you calculate the inertia of the chicken soup and the clam? Here’s the mathematical formulas from the back of a Dynamics textbook (a typical course that all Engineers take during their 2nd year of college).

Inertia of a solid cylinder = 1/2 * (mr²)
Inertia of a cylindrical shell = 1/12 * (mr²)

If the radius of the soup is 6.5 cm and the mass for both is the same (345 grams, or 0.345kg), and the mass of an empty can is 45 grams, then:

(CLAM) Inertia of a solid cylinder = 1/2 * (mr²) = 1/2 * (0.345kg)*(6.5cm)² = 7.29 kg cm²
(CHICKEN) Inertia of a cylindrical shell = 1/12 * (mr²) = 1/12 * (0.045kg) *(6.5cm)² = 0.158 kg cm²

The numerical value for the solid cylinder is larger than the shell, which tells us that it has a greater resistance to rolling and will start to rotate much slower than the shell. This makes logical sense, as it’s easier to get the shell alone to rotate than move a solid cylinder. Remember, you must use the mass of the cylinder shell (empty can) when calculating the chicken’s inertia, as the broth itself does not rotate and this does not have a ‘rolling resistance’!

Advanced students: Download your Chicken and Clam Lab here.

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If I toss a ball horizontally at the exact same instant that I drop another one from my other hand, which one reaches the ground first? For this experiment, you need: [am4show have=’p8;p9;p11;p38;p72;p92;’ guest_error=’Guest error message’ user_error=’User error message’ ]

• 2 rulers or paint sticks. Any thing wide and flat
• 2 coins or poker chips
• A sharp eye and ear
• A partner is good for this one too

Download Student Worksheet & Exercises
1. Place one of the rulers flat so that it is diagonal across the edge of a table with half the ruler on the table and half sticking off.

2. Place one coin on the table, just in front of the ruler and just behind the edge of the table. Place the other coin on the ruler on the side where it’s off the table.

3. Put your finger right in the middle of the ruler on the table so that you are holding it in such a way that it can spin a bit under your finger. Now with the other ruler you are going to smack the end of the first ruler so that the first ruler pushes the coin off the desk and the coin that’s resting on the ruler falls to the ground.

4. Now, before you smack the ruler, make a prediction. Will the coin that falls straight down or the coin that is flying forward hit the ground first?

5. Try it. Do the test and look and listen carefully to what happens. It’s almost better to use your ears here than your eyes. Do it a couple of times.

Are you surprised by what you see and/or hear? Most people are. It’s not what you would expect.

The coins hit the ground at the SAME time. Is that odd or what?

Did you read the first sentence at the top of this lab? What do you think will happen?

The balls will hit the ground at the exact SAME time.

Gravity doesn’t care if something is moving horizontally or not. Everything falls toward the center of the Earth at the same rate.

Let me give you a better example: A bullet fired parallel to the ground from a gun and a bullet dropped from the same height at the same time will both hit the ground at the same time. Even though the one fired lands a mile away! It seems incredible, but it’s true.

Gravity doesn’t care what size something is or whether or not it is moving, Gravity treats all things equally and accelerates them the same.

Notice, that I say gravity accelerates all things equally, not gravity pulls on all things equally. Gravity does pull harder on some things than on other things. This is why I weigh more than a dog. I am made of more stuff (I have more atoms) than the average dog, so gravity pulls on me more.

Weight is nothing more than a measure of how much gravity is pulling on you. This is why you can be “weightless” on a scale in space. You are still made of stuff, but there’s a balance of the gravity that is pulling on you and the outward force due to the acceleration since you’re moving in a circle (which you do in order to remain in orbit), so it feels like you have no weight.

The larger a body is, the more gravitational pull or the larger a gravitational field it will have.

The Moon has a fairly small gravitational field (if you weighed 100 pounds on Earth, you’d only be 17 pounds on the Moon), the Earth’s field is fairly large and the Sun has a HUGE gravitational field (if you weighed 100 pounds on Earth, you’d weigh 2,500 pounds on the sun!).

As a matter of fact, both the dog and I both have gravitational fields! Since we are both bodies of mass we have a gravitational field which will pull things towards us. All bodies have a gravitational field. However, my mass is sooooo small that the gravitational field I have is miniscule. Something has to be very massive before it has a gravitational field that noticeably attracts another body.

So what’s the measurement for how much stuff you’re made of? Mass. Mass is basically a weightless measure of how much matter makes you, you. A hamster is made of a fairly small amount of stuff so she has a small mass. I am made of more stuff, so my mass is greater than the hamster’s. Your house is made of even more stuff so its mass is greater still.

So, here’s a question. If you are “weightless” in space, do you still have mass? Yes, the amount of stuff you’re made of is the same on Earth as it is in your space ship. Mass does not change but since weight is a measure for how much gravity is pulling on you, weight will change.

Did you notice that I put weightless in quotation marks? Wonder why?

Weightlessness is a myth! Believe it or not, one is never weightless. A person can be pretty close to weightless in very deep space but the astronauts in a space ship actually do have a bit of weight.

Think about it for a second. If a space ship is orbiting the Earth what is it doing? It’s constantly falling! If it wasn’t moving forward at 10’s of thousands of miles an hour it would hit the Earth. It’s moving fast enough to fall around the curvature of the Earth as it falls but, indeed, it’s falling as the Earth’s gravity is pulling it to us.

Otherwise the ship would float out to space. So what is the astronaut doing? She’s falling too! The astronaut and the space ship are both falling to the Earth at the same rate of speed and so the astronaut feels weightless in space. If you were in an elevator and the cable snapped, you and the elevator would fall to the Earth at the same rate of speed. You’d feel weightless! (Don’t try this at home!)

Exercises

1. True or false? Gravity pulls on all things equally.
2. True or false? Gravity accelerates all things equally.
3. In your own words, why do the coins hit the ground at the same time? Is this what you’d expect to happen on Mars?

The rest of this experiment is for advanced students…[/am4show]

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For advanced students:

Either now, or at some point in the future you may ask yourself this question, “How can gravity pull harder (put more force on some things, like bowling balls) and yet accelerate all things equally?” When we get into Newton’s laws in a few lessons you’ll realize that doesn’t make any sense at all. More force equals more acceleration is basically Newton’s Second law.

Well, I don’t want to take too much time here since this is a little deeper then we need to go but I do feel some explanation is in order to avoid future confusion. The explanation for this is inertia. When we get to Newton’s First law we will discuss inertia. Inertia is basically how much force is needed to get something to move or stop moving.

Now, lets get back to gravity and acceleration. Let’s take a look at a bowling ball and a golf ball. Gravity puts more force on the bowling ball than on the golf ball. Soooo the bowling ball should accelerate faster since there’s more force on it. However, the bowling ball is heavier soooo it is harder to get it moving. Vice versa, the golf ball has less force pulling on it but it’s easier to get moving. Do you see it? The force and inertia thing equal out so that all things accelerate due to gravity at the same rate of speed!

Gravity had to be one of the first scientific discoveries. Whoever the first guy was to drop a rock on his foot, probably realized that things fall down! However, even though we have known about gravity for many many years, it still remains one of the most elusive mysteries of science. At this point, nobody knows what makes things move towards a body of mass.

Why did the rock drop towards the Earth and on that guy’s foot? We still don’t know. We know that it does, but we don’t know what causes a gravitational attraction between objects. Gravity is also a very weak force. Compared to magnetic forces and electrostatic forces, the gravitational force is extremely weak. How come? No one knows. A large amount of amazing brain power is being used to discover these mysteries of gravity. Maybe it will be you who figures this out!

Advanced students: Download your Forever Falling Lab here.

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This lesson may give you a sinking sensation but don’t worry about it. It’s only because we’re talking about gravity. You can’t go anywhere without gravity. Even though we deal with gravity on a constant basis, there are several misconceptions about it. Let’s get to an experiment right away and I’ll show you what I mean.

If I drop a ping pong ball and a golf ball from the same height, which one hits the ground first? How about a bowling ball and a marble?

Here’s what you need:

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• ping pong ball
• golf ball
• you

 
Download Student Worksheet & Exercises

For this experiment, you’ll need:

Two objects of different weights. A marble and a golf ball, or a tennis ball and a penny for example.
A sharp eye
A partner

1. Take a careful look at both objects and make a prediction about which object will hit the ground first if they are dropped from the same height.

2. Test your prediction. Hold both objects at the same height. Make sure the bottom of both objects are the same distance from the floor.

3. Let them go as close to the same time as possible. Sometimes it’s helpful to roll them off a book.

4. Watch carefully. Which hits the ground first, the heavier one or the lighter one? Try it a couple of times and watch carefully. It will be a little easier for the person who isn’t dropping them to see what happens.

What you should see is that both objects hit the ground at the same time! Gravity accelerates both items equally and they hit the ground at the same time. Any two objects will do this, a brick and a Buick, a flower and a fish, a kumquat and a cow!

“But,” I hear you saying, “if I drop a feather and a flounder, the flounder will hit first every time!” Ok, you got me there. There is one thing that will change the results and that is air resistance.

The bigger, lighter and fluffier something is, the more air resistance can effect it and so it will fall more slowly. Air resistance is a type of friction which we will be talking about later. In fact, if you removed air resistance, a feather and a flounder would hit the ground at the same time!!!

Where can you remove air resistance? The moon!!! One of the Apollo missions actually did this (well, they didn’t use a flounder they used a hammer). An astronaut dropped a feather and a hammer at the same time and indeed, both fell at the same rate of speed and hit the surface of the moon at the same time.

Ask someone this question: Which will hit the ground first, if dropped from the same height, a bowling ball or a tennis ball? Most will say the bowling ball. In fact, if you asked yourself that question 5 minutes ago, would you have gotten it right? It’s conventional wisdom to think that the heavier object falls faster. Unfortunately, conventional wisdom isn’t always right. Gravity accelerates all things equally. In other words, gravity makes all things speed up or slow down at the same rate. We will be discussing acceleration more in a later lesson. If you would like more details on the math of this, it will be at the end of this lesson in the Deeper Lesson section.

This is a great example of why the scientific method is such a cool thing. Many, many years ago, there was a man of great knowledge and wisdom named Aristotle. Whatever he said, most people believed to be true. The trouble was he didn’t test everything that he said. One of his statements was that objects with greater weight fall faster than objects with less weight. Everyone believed that this was true.

Hundreds of years later Galileo came along and said “Ya know…that doesn’t seem to work that way. I’m going to test it” The story goes that Galileo grabbed a melon and an orange and went to the top of the Leaning Tower of Pisa. He said, “Look out below!” and dropped them! By doing that, he showed that objects fall at the same rate of speed no matter what their size.

It is true that it was Galileo who “proved” that gravity accelerates all things equally no matter what their weight, but there is no real evidence that he actually used the Leaning Tower of Pisa to do it.

Advanced Students: Download your Gravity Lab here.

Exercises

1. What did you notice from your data? Did heavier or lighter objects fall faster? Did more massive objects or smaller objects fall faster? What characteristic seemed to matter the most?
2. Is gravity a two-way force, like the attractive-repulsive forces of a magnet?
3. If I were to drop a bowling ball and a balloon filled with a gas six times heavier than air (sulfur hexafluoride SF₆) and inflated to the exact size of the bowling ball from my roof, which will strike the ground first?

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It is very rare, especially on Earth, to have an object that is experiencing force from only one direction. A bicycle rider has the force of air friction pushing against him. He has to fight against the friction between the gears and the wheels. He has gravity pulling down on him. His muscles are pushing and pulling inside him and so on and so on.

Even as you sit there, you have at least two forces pushing and pulling on you. The force of gravity is pulling you to the center of the Earth. The chair is pushing up on you so you don’t go to the center of the Earth. So with all these forces pushing and pulling, how do you keep track of them all? That’s where net force comes in.

The net force is when you add up all of the forces on something and see what direction the overall force pushes in. The word “net”, in this case, is like net worth or net income. It’s a mathematical concept of what is left after everything that applies is added and subtracted. The next activity will make this clearer.

Here’s what you need:

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• a rope (at least 3 feet long is good)
• a friend
• a sense of caution

(Be careful with this. Don’t pull too hard and please don’t let go of the rope. This is fun but you can get hurt if you get silly.)

 
Download Student Worksheet Exercises

1. You and your friend each grab an opposite end of the rope.
2. Both of you pull just a bit on the rope.
3. Have your friend pull a bit harder than you. Notice the direction that you both move.
4. Now you pull harder than your friend. Now which way do you go?
5. Lastly, both of you pull with the same strength on the rope. Even though you are both pulling, neither one of you should move.

In this experiment, there were always at least three forces pulling on the rope. Can you think of the three? They are you, your friend and gravity. You were pulling in one direction. Your friend was pulling in another direction and gravity was pulling down.

When one of you pulled harder (put more force on the rope) than the other person, there was a net force in the direction of the stronger pull. The rope and you guys went in that direction.

When both of you were pulling the same amount, there was an equal force pulling the rope one way and another equal force pulling the rope the other way. Since there were two equal forces acting in two opposite directions, the net force equaled zero, so there was no movement in either direction. No net force in this case means no movement.

As you’ll see when you learn about Newton’s second law, no net force means no acceleration.

Let’s take another look at the bicycle rider we talked about earlier. To make things easier, we’ll call him Billy. For Billy to speed up, he needs to win the tug of war between all of the forces involved in riding a bicycle. In other words, his muscles need to put more force on the forward motion of the bike than all of the forces of friction that are pushing against him.

If he wants to slow down, he needs to allow the forces of friction to win the tug of war so that they will cancel out his forward motion and slow down the bike. If he wants to ride at a steady speed, he wants the tug of war to be tied. His muscles need to exert the same amount of force pushing forward as the friction forces pulling in other directions.

Advanced Students: Download your Net Forces Lab here.

Exercises:

1. For scenario 1, in which direction did you both move?  Draw the free body diagram below
2. For scenario 2, in which direction did you both move?  Draw the free body diagram below
3.  For scenario 3, in which direction did you both move?  Draw the free body diagram below
4. For scenario 4, in which direction did the rope move?  Draw the free body diagram below
5. What was the same about question 1 and question 4?  What was different?
6.  Even though the forces were less in question 1 than question 4, what was the net force for both?
7.  There were always at least 3 forces acting on the rope, what were they?  Did you include the third force in your free body diagram?
8. If the rope wasn’t moving, but you had only one force moving down, what does that tell you about the force you and your friend exerted?

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Did you know that your cereal may be magnetic? Depending on the brand of cereal you enjoy in the morning, you’ll be able to see the magnetic effects right in your bowl. You don’t have to eat this experiment when you’re done, but you may if you want to (this is one of the ONLY times I’m going to allow you do eat what you experiment with!) For a variation, pull out all the different boxes of cereal in your cupboard and see which has the greatest magnetic attraction.

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Materials:

• a bowl of cereal with milk
• spoon

 
Download Student Worksheet & Exercises

1. Fill the bowl with milk.
2. Put about 20 pieces of cereal (not the whole box!) into the bowl.
3. Stir up the bowl a little and watch what happens.

If you watched carefully, you saw that as the cereal “O’s” got close to one another, they attracted each other. The closer they got, the stronger was their attraction to each other and the faster they moved towards each other. If you wait and watch long enough, you get a nice tight batch of cereal all clustered together in one or two big blobs. This activity is a great illustration of what is meant by the inverse square law because the attraction between “O’s” was stronger the closer they got to each other.

I discovered this activity one morning as I was eating cereal. The same thing happens with bubbles when you’re doing the dishes. Science is everywhere! Feel free to eat the cereal!

Exercises 

1. Why do the pieces of cereal stick to each other?
2.  Does the cereal move slower or faster the closer the pieces come in contact with each other?
3.  What other cereals does it work for?

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Have you ever been close to something that smells bad? Have you noticed that the farther you get from that something, the less it smells, and the closer you get, the more it smells? Well forces sort of work in the same way.

Forces behave according to a fancy law called the inverse-square law. To be technical, an inverse-square law is any physical law stating that some physical quantity or strength is inversely proportional to the square of the distance from the source of that physical quantity.

The inverse-square law applies to quite a few phenomena in physics. When it comes to forces, it basically means that the closer an object comes to the source of a force, the stronger that force will be on that object. The farther that same object gets from the force’s source, the weaker the effect of the force.

Mathematically we can say that doubling the distance between the object and the source of the force makes the force 1/4th as strong. Tripling the distance makes the force 1/9th as strong. Let’s play with this idea a bit.

Here’s what you need:

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• magnet
• paper clip
• string
• tape

Using a magnet (the stronger the better), paper clip, string (or yarn or even dental floss!), and tape, you can make a flying paper clip.

OPTIONAL: If you happen to have a spring scale and ruler, get those out, too…otherwise, just skip these items – they are not essential to understanding the concept here.

 
Download Student Worksheet & Exercises

1. Tie about 4 inches of string to a paper clip.
2. Tape the magnet to the table.
3. Hold the end of the string that is not tied to the paper clip and let the paper clip dangle.
4. Slowly bring the paper clip closer and closer to the magnet.
5. Notice that the closer you get to the magnet, the stronger the force of the magnetic field is on the paper clip.

If you have a spring scale:
6. Attach the paper clip to the spring scale.
7. Move the paper clip closer to the magnet until the magnetic field affects the paper clip.
8. Measure how far the paper clip is from the magnet with a ruler.
9. Measure how much pull there is on the paper clip. Use newtons if your spring scale shows that measurement, but grams are OK if it doesn’t.
10. Bring the paper clip a half inch closer and measure the force of the pull again either in grams or Newtons.
11. Continue to get closer to the magnet half an inch at a time, measuring the force until you can’t get any closer.

What you may have noticed here was that the closer you got the paper clip to the magnet (the object causing the force field) the stronger the force was on the paper clip. You have just seen the inverse-square law in action!

Exercises: 

1. Circle one: The closer you get to the magnet, the (stronger | weaker) the force of the magnetic field is on the paper clip.
2. Why does it matter which way you orient the magnet in this experiment?
3. Which magnet has the strongest magnetic field?
4. Is the north or south pole stronger on a magnet?

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You are actually fairly familiar with electric fields too, but you may not know it. Have you ever rubbed your feet against the floor and then shocked your brother or sister? Have you ever zipped down a plastic slide and noticed that your hair is sticking straight up when you get to the bottom? Both phenomena are caused by electric fields and they are everywhere!

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An electric field exists when at least one body is electrically charged. Atoms are filled with positively charged protons and negatively charged electrons. If an object has more electrons than protons, it will be negatively charged and if it has fewer electrons than protons, it will be positively charged. Electric fields, like magnetic fields, can attract and repel. If two bodies have the same kind of charge, that is either both are negative or both are positive, they will push themselves away from each other. If one body has a positive charge and the other has a negative charge, they will attract each other. Charged bodies can also attract bodies that are neither positive nor negative but are just neutral.

Electric fields are extremely common. If you comb your hair with a plastic comb, you cause that comb to have a small electric field. When you take off a fleece jacket or a polyester sweat shirt, you create an electric field that may be thousands of volts! Don’t worry, you can’t get hurt. There may be lots of voltage but there will be very little amperage. It’s the amperage that actually hurts you.

Here’s a simple experiment you can do that only needs four simple items:
– head of hair
– balloon
– yardstick or meterstick
– large spoon

Here’s what you do:

 
Download Student Worksheet & Exercises

Make sure you’ve tried out these Static Electricity experiments and learn how to light a bulb without plugging it into the wall!

Exercises 

1. What happens if you rub the balloon on other things, like a wool sweater?
2. If you position other people with charged balloons around the table, can you keep the yardstick going?
3.  Can we see electrons?
4.  How do you get rid of extra electrons?
5.  Does the shape of the balloon matter?
6.  Does hair color matter?
7.  Rub a balloon on your head, and then lift it up about 6”. Why is the hair attracted to the balloon?
8. Why does the hair continue to stand on end after the balloon is taken away?
9. What other things does the balloon stick to besides the wall?
10. Why do you think the yardstick moved?
11. What other things are attracted or repelled the same way by the balloon? (Hint: try a ping pong ball.)

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The electromagnetic field is a bit strange. It is caused by either a magnetic field or an electric field moving. If a magnetic field moves, it creates an electric field. If an electric field moves, it creates a magnetic field.

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A moving electric field creates a moving magnetic field, which creates a moving electric field, which creates a moving magnetic field and on and on. Pretty strange huh? So an electromagnetic field is both an electric field and a magnetic field all rolled into one. Light, radio waves, and microwaves are examples of electromagnetic waves created by moving self-creating electronic and magnetic fields.

Until 1820, magnetic fields and electric fields were thought of as two completely separate things. A fellow by the name of Hans Christian Ørsted was preparing for a lecture when he noticed that a compass needle jumped when he flipped a switch that caused electricity to flow through some wires. This chance observation caused him to investigate further and discover that electric fields create magnetic fields and vice-versa.

Thus, through a completely random observation, electromagnetism was discovered. Without that discovery we wouldn’t have electric engines, radios, cell phones, television or Filbert the Flounder electric toothbrushes! Hooray for Ørsted!

A Summary of Force Fields and Objects

The rest of this experiment (below) is for advanced students: (Hint: you need to have access to upper level content.)
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Measuring the Earth’s Magnetic Pulse

When you stare at a compass, the needle that indicates the magnetic field from the Earth appears to stand still, but we’re going to find how it fluctuates and moves by creating a super-sensitive instrument using everyday materials (for comparison, you would spend over $100 for a scientific instrument that does the same thing).

Today you get to learn how to amplify tiny pulses in the Earth’s magnetic field using a laser and a couple of magnets. It’s a very cool experiment, but it does take patience to make it work right.

Materials

• Index card or scrap of cardboard
• 2 small mirrors
• 2 rare earth magnets
• Nylon filament (thin nylon thread works, too)
• 4 doughnut magnets
• Laser pointer (any kind will work – even the cheap key-chain type)
• Clean glass jar (pickle, jam, mayo, etc… any kind of jar that’s heavy so it won’t knock over easily)
• Wooden spring-type clothespin
• Hot glue gun, scissors and tape

Download Student Worksheet & Exercises

1. Sandwich the twine between the two rare earth magnets. These are the stronger magnets.
2. Use a tiny dab of glue on one of the magnets and attach a mirror to the magnet. Do this on the other side for the second magnet and mirror.
3. Lower the mirror-magnets into the container, leaving it hanging an inch above the bottom of the jar. Cut the twine at the mouth level of the container.
4. Glue the top of the twine to the bottom of the lid, right in the center.
5. When the glue has dried, place your mirror-magnets inside the jar and close the lid. Make sure that the mirror-magnets don’t touch the side of the jar, and are free to rotate and move.
6. You’ve just built a compass! The small magnets will align with the Earth’s magnetic field. Slowly rotate the jar, and watch to see that the mirror-magnets inside always stay in the same configuration, just like the needle of a standard compass.
7. Set your new compass aside and don’t touch it. You want the mirror-magnets to settle down and get very still.
8. You are going to build the magnet array now. Stack your four doughnut magnets together in a tall stack.
9. Fold your index card in half, and then open it back up. On one side of the crease you’re going to glue your magnets. When the magnets are attached, you’ll fold the card over so that it sits on the table like a greeting card with the magnets facing your glass jar.
10. Tape your index card down to the table as you build your magnet array. (Otherwise the paper will jump up mid-way through and ruin your gluing while you are working.)
11. Place a strip of glue on the bottom magnet of your stack and press it down onto the paper, gluing it into place.
12. Lift the stack off (the bottom magnet should stay put on the paper) and place glue on the bottom magnet. Glue this one next to the first.
13. Continue with the array so you have a rectangle (or square) arrangements of magnets with their poles oriented the same way. Don’t flip the magnets as you glue them, or you’ll have to start over to make sure they are lined up right.
    Since we live in a gigantic magnetic field that is 10,000 times more powerful than what the instrument is designed to measure, we have to “zero out” the instrument. It’s like using the “tare” or “zero” function on a scale. When you put a box on a scale and push “zero”, then the scale reads zero so it only measures what you put in the box, not including the weight of the box, because it’s subtracting the weight of the box out of the measurement. That’s what we’re going to do with our instrument: we need to subtract out the Earth’s magnetic field so we just get the tiny fluctuations in the field.
14. Place your instrument away from anything that might affect it, like magnets or anything made from metal.
15. Fold the card back in half and stand it on the table. We’re normally going to keep the array away from the jar, or the magnet array will influence the mirror-magnets just like bringing a magnet close to a compass does. But to zero out our instrument, we need to figure out how far away the array needs to be in order to cancel out the Earth’s field.
16. Bring the array close to your jar. You should see the mirror-magnets align with the array.
17. Slowly pull the magnet array away from the compass to a point where if it were any closer, the mirror-magnets would start to follow it, but any further away and nothing happens. It’s about 12 inches away. Measure this for your experiment and write it on your array or jar so you can quickly realign if needed in the future.
18. Insert your laser pointer into the clothespin so that the jaws push the button and keep the laser on. Place it at least the same distance away as the array. You might have to prop the laser up on something to get the height just right so you can aim the laser so that it hits the mirror inside. (Note that you’ll have a reflection from the glass as well, but it won’t be nearly as bright.)
19. Find where the laser beam is reflected off the mirror and hits the wall in your room. Walk over and tape a sheet of paper so that the dot is in the middle of the paper. Use a pen and draw right on top of the dot, and mark it with today’s date.
20. Do you notice if it moves or it is stays put? Sometimes the dot will move over time, and other times the dot will wiggle and move back and forth. The wiggles will last a couple of seconds to a couple of minutes, and those are the oscillations and fluctuations you are looking for!
21. Tape a ruler next to the dot so you can measure the amount of motion that the dot makes. Does it move a lot or a little when it wiggles? Two inches or six?

What’s Going On?

The reason this project works is because of tiny magnetic disturbances caused by the ripples in the ionosphere. Although these disturbances happen all the time and on a very small scale (usually only 1/10,000th of the Earth’s magnetism strength), we’ll be able to pick them up using this incredibly simple project. Your reflected laser beam acts like an amplifier and picks up the movement from the magnet in the glass.

Construction tip for experiment:
You need to use a filament that doesn’t care how hot or humid it is outside, so using one of the hairs from your head definitely won’t work. Cotton tends to be too stretchy as well. Professionals use fine quartz fibers (which are amazingly strong and really don’t care about temperature or humidity). Try extracting a single filament from a multi-stranded nylon twine length about 30″ long. If you happen to have a fine selection of nylon twine handy, grab the one that is about 25 microns (0.01″) thick. Otherwise, just get the thinnest one you can find.

You can tape a wooden clothespin down to the table and insert your laser pointer inside – the jaws will push the button of the laser down so you can watch your instrument and take your measurements. When you’re ready, tape a sheet of paper to the wall where your reflected beam (reflected from the mirror, not the glass… there will be two reflected beams!) hits the wall and mark where it hits. Over periods of seconds to minutes, you’ll see deflections and oscillations (wiggles back and forth) – you are taking the Earth’s magnetic pulse!

In order for this experiment to work properly, ALL magnets (including the penny described below) need to be in the same plane. That is, they all need to be the same height from the ground. You can, of course, rotate the entire setup 90 degrees to investigate the magnetic ripples in the other planes as well!

To make this instrument even more sensitive, glue a copper penny (make sure it’s minted before 1982, or you’ll get an alloy, not copper, penny) to the glass jar just behind the magnets (opposite the laser). When your magnets move now, they will induce eddy currents in the penny that will induce a (small) magnetic field opposite of the rotation of the magnets to dampen out “noise” oscillation. In short, add a penny to the glass to make your instrument easier to read.

Also, note that big, powerful magnets will not respond quickly, so you need a lightweight, powerful magnet.

You can walk around with your new instrument and you’ll find that it’s as accurate as a compass and will indicate north. You probably won’t see much oscillation as you do this. Because the Earth has a large magnetic field, you have to “tare” the instrument (set it to “zero”) so it can show you the smaller stuff. Use the doughnut magnets about 30 centimeters away as shown in the video.

Exercises

1. Does the instrument work without the magnet array?
2. Why did we use the stronger magnets inside the instrument?
3. Which planet would this instrument probably not work on?

Advanced Students: Download your Electromagnetic Field Lab here.

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Remember, there are four different kinds of forces: strong nuclear force,
electromagnetism, weak nuclear force, and gravity. There are also four basic force fields that you come into contact with all the time. They are the gravitational field, the electric field, the magnetic field, and the electromagnetic field. Notice that those four force fields really only use two of the four different kinds of force: electromagnetism and gravity. Let’s take a quick look at what causes these four fields and what kind of objects they can affect, starting with the magnetic field.

Here’s what you need:
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• you
• a compass

You’re probably fairly familiar with magnetic fields. If you’ve ever stuck a magnet to a refrigerator, you’ve taken advantage of magnetic fields. Sticking a magnet to a refrigerator is one of those every day experiences that should just be absolutely flabbergasting. There you are holding an “I’d Rather be Relative” magnet and it sticks to the fridge! But wait a minute, if you put it on the wall… it falls off! How does it “know” what to stick to? Not only does it stick to the fridge, it also pushes some things away, attracts other things and couldn’t care less about still other things. What’s that all about?! We rarely think about what magnets do but, wow, the things they do are weird!

Magnetic fields come from objects that have a surplus of electrons all moving in the same direction. This can be an electric wire with current running through it or one of several special types of metals. Iron, nickel and cobalt are the most common metals that can be magnetic. Magnetic fields can only affect objects that can be magnetic themselves. That’s why a magnet can attract an iron nail, but it can’t attract an aluminum can. The iron nail can be magnetic, but the aluminum cannot. Magnets can also be attractive or repulsive. Two magnets with the same kind of poles facing one another will push themselves apart. Two magnets with opposite poles facing one another will pull themselves together.

 
Download Student Worksheet & Exercises

Using a compass and the Earth, you can do a simple experiment to detect the magnetic field of our planet. (If you don’t have a compass, just slide a magnet along the length of a needle several times (make sure you only swipe in one direction!) then stick it through a cork or bit of foam. Float the needle-foam thing in a cup of water.)

1. Look at the compass

2. Walk anywhere and keep your eye on the compass.

3. Turn around in circles and keep your eye on the compass (don’t get too dizzy).

Again a very simple little activity, but I hope you can see the point. No matter where you went or what you did, that needle always pointed the same direction! The Earth’s magnetic force field, another strange and mysterious force, always pushes that needle in the same direction. It’s invisible and you can’t feel it…but the needle can!

 Exercises 

1. Why does the needle need the foam?
2.  Why do we use water?
3. What are the forces in a magnetic field?

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Ok, sort of a silly experiment I admit. But here’s what we’re going for – there is an invisible force acting on you and the ball. As you will see in later lessons, things don’t change the way they are moving unless a force acts on them. When you jump, the force that we call gravity pulled you back to Earth. When you throw a ball, something invisible acted on the ball forcing it to slow down, turn around, and come back down. Without that force field, you and your ball would be heading out to space right now!
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Here’s what you need:

• you
• the Earth (or any planet that’s convenient)
• a ball

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Download Student Worksheet & Exercises

Here’s what you do:

1. Jump!
2. Carefully observe whether or not you come back down.
3. Take the ball and throw it up.
4. Again, watch carefully. Does it come down?

Gravity is probably the force field you are most familiar with. If you’ve ever dropped something on your foot you are painfully aware of this field! Even though we have known about this field for a looooong time, it still remains the most mysterious field of the four.

What we do know is that all bodies, from small atoms and molecules to gigantic stars, have a gravitational field. The more massive the body, the larger its gravitational field. As we said earlier, gravity is a very weak force, so a body really has to be quite massive (like moon or planet size) before it has much of a gravitational field. We also know that gravity fields are not choosy. They will attract anything to them.

All types of bodies, from poodles to Pluto, will will attract and be attracted to any other type of body. One of the strangest things about gravity is that it is only an attractive force. Gravity, as far as we can tell, only pulls things towards it. It does not push things away. All the other forces are both attractive (pull things towards them) and repulsive (push things away). (Gravity will be covered more deeply in a later lesson.)

Exercises 

1. What did you determine about gravity and how it affects the rate of falling?
2. Did changing the object affect the rate of falling? Why or why not?
3. Did changing the variable affect the rate of falling?  Why or why not?

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Advanced students: Download your Gravitational Force Lab here.

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• you
• the Earth (or any planet that’s convenient)
• a ball

4SHOW TEST END

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