Junk Drawer Physics: 50 Awesome Experiments That Don't Cost a Thing

Junk Drawer Physics: 50 Awesome Experiments That Don't Cost a Thing

by Bobby Mercer

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Overview

A children’s instructional book on how to use readily available materials to turn the house into a science lab

Physics teacher Bobby Mercer provides readers with more than 50 great hands-on experiments that can be performed for just pennies, or less. Turn a plastic cup into a pinhole camera using waxed paper, a rubber band, and a thumbtack. Build a swinging wave machine using a series of washers suspended on strings from a yardstick. Or construct your own planetarium from an empty potato chip canister, construction paper, scissors, and a pin. Each project has a materials list, detailed step-by-step instructions with illustrations, and a brief explanation of the scientific principle being demonstrated. Junk Drawer Physics also includes sidebars of fascinating physics facts, such as did you know the Eiffel Tower is six inches taller in summer than in winter because its steel structure expands in the heat? Educators and parents will find this title a handy resource to teach children about physics topics that include magnetism, electricity, force, motion, light, energy, sound, and more, and have fun at the same time.

Product Details

ISBN-13: 9781613749203
Publisher: Chicago Review Press, Incorporated
Publication date: 06/01/2014
Series: Junk Drawer Science Series
Pages: 208
Sales rank: 534,212
Product dimensions: 6.00(w) x 8.80(h) x 0.60(d)
Lexile: 890L (what's this?)
Age Range: 9 - 13 Years

About the Author

Bobby Mercer is a high school physics teacher and the author of several books, including The Flying Machine Book, How Do You Light a Fart?, Quarterback Dad, and Smash It! Crash It! Launch It! He lives outside of Asheville, North Carolina.

Read an Excerpt

Junk Drawer Physics

50 Awesome Experiments That Don't Cost a Thing


By Bobby Mercer

Chicago Review Press Incorporated

Copyright © 2014 Bobby Mercer
All rights reserved.
ISBN: 978-1-61374-923-4



CHAPTER 1

Forces and Motion


Mesmerizing CD Top

Turn an old CD into a mind-bending tabletop spinner. Spin, stare, and watch the world change.

Adult supervision required


From the Junk Drawer:

[] Old CD

[] Paper

[] Markers

[] Scissors

[] Superglue or hot glue

[] 2 flat glass beads


Step 1: Trace around a CD on a piece of paper. Use a marker to create swirls going out from the center, as shown. Then cut around the outside of the CD line.

Step 2: You need adult permission or help for this step. Lay a piece of scrap paper on your work surface to catch any glue that drips. Use hot glue or superglue to affix the round piece of paper to the CD. Then glue one glass bead to each side of the hole in the center of the CD, with the flat sides facing the hole. These glass beads are commonly found in craft stores and are used as decorations for flower vases, tabletop water fountains, and candle sets. Let the glue dry completely.

Step 3: If you color in the swirls, it will make them wider, which will make the illusion better.

Step 4: Pinch the top glass bead with your fingers and spin it. Practice until you can get it to spin like a top while sitting in place.

Step 5: Now spin the top and lean directly over it. Stare at the center for about 30 seconds as it spins, then look up at a plain wall. It should make the wall spin a little bit. Keep practicing until you master it.

Try staring at the top for different amounts of time. Crazy! Do it again and look at other things. Amaze your friends as you warp the world around you. You can make other tops and try different patterns and colors.


The Science Behind It

The spiral on the top of the CD "trains" your eyes to follow the swirl. This effect is called persistence of vision. Your brain holds onto an image for a fraction of a second. Since that image is a spinning spiral, when you look at a wall or something else, it will spiral for a few seconds. It might take a few tries to get good at it. (Even if you don't always get the swirl effect, you still made a fun top.)


Grocery List Tug-of-War

Use a piece of paper to learn about inertia.


From the Junk Drawer:

[] Several strips of paper

[] Scissors

[] Coins

[] Tape


Step 1: For this experiment, you need several strips of paper. A long grocery list notepad will work, or you can take a sheet of letter size paper and cut it into four strips. Paper that is already written on is perfect — you're recycling.

In each strip, make two cuts that almost go through the paper, as shown. To do this, fold each strip of paper, but do not crease the center. This will insure the cuts are equal in length.

Step 2: Pick up a single strip, holding one end in each hand. Your goal is to try to tear both ends off at the same time so that you are left with just the center part. First, pull slowly and watch what happens. Then repeat with another strip and try pulling faster. Can you do it?

Step 3: Now tape four or five coins to the center section of a cut strip.

Step 4: Quickly pull on the ends of the strip and watch what happens this time. The trick is to pull fast and hard.

The Science Behind It

Inertia is the tendency of an object to resist changes in motion. A heavy object is hard to start moving, but a heavy object is also harder to stop once it is moving. Just think of a semitruck on the interstate and how long it takes to come to a stop.

When you try this experiment with paper alone, the center piece doesn't have much inertia — it's light. When you tug it, one end tears before the other, leaving two pieces together. But when you tape coins to the center section, you give that section extra inertia. This time, when you tug quickly, the center section wants to stay in place more than before (it has more inertia). The ends tear off, leaving you with just the center.


Jar Spin

Defy gravity as you take a ball for a spin.


From the Junk Drawer:

[] Clear, large-mouth plastic jar (mayonnaise or peanut butter jars work well) with label removed

[] Small bouncy ball


Step 1: Place a clear plastic jar mouth-down over a small bouncy ball. (Don't do this on a nice wooden table.) Ping-pong balls also work well.

Step 2: Grasp the bottom of the jar. While keeping the jar's mouth on the table, swirl the jar quickly in small circles, causing the ball to roll in circles as well. Move the jar faster, until you can pick up both the jar and the ball.


The Science Behind It

As you swirl the jar in a circle, the ball wants to move in a straight line. Of course, it can't, because the jar is in the way. The jar supplies a centripetal (center-seeking) force on the ball. The ball pushes back against this centripetal force, which creates friction between the inside of the jar and the ball. When the speed of the ball is great enough, the friction will keep the it "glued" to the inside wall as you lift the jar.


Floating Coin

Magically lift a coin with science.


From the Junk Drawer:

[] Crisp dollar bill (or piece of paper)

[] Coin


Step 1: Fold a dollar bill in half so it forms a V, as shown. You can also do this with a stiff piece of paper. Place the coin over the V.

Step 2: Slowly pull apart the two ends of the dollar bill. The coin should stay in place and balance on the paper. Now slowly lift the dollar bill, picking up the coin with it. With practice and a steady hand, you can pick up the coin even when the bill is completely straight. Practice this trick, then amaze your parents, friends, and teachers.


The Science Behind It

All objects have a center of mass. If the center of mass is over a support, the object will stay balanced. When you balance on one foot, you have to move your center of mass over that foot. Try it; as you lift one foot up, your body will naturally move your center of mass over the other foot. Similarly, when you slowly pull the ends of the dollar bill, the center of mass for the coin will move directly over the dollar bill. As long as the center of mass stays over the supporting object, you can pick up the coin.


Crash Test Dummy

Learn Newton's laws with a dummy to help.


From the Junk Drawer:

[] Toy car

[] Small action figure

[] Rubber band

[] Large marshmallow


Step 1: Set a crash test dummy — a plastic action figure — on a toy car. Push the toy car into a wall. What happens to the dummy?

Step 2: Put the crash test dummy back on the car. This time, use a rubber band to attach the dummy to the roof. Make sure the rubber band does not interfere with the wheels. Push the toy car into a wall again. What happens?

Step 3: Put the action figure on the car one last time. Use a rubber band seat belt, but add a large marshmallow to act as an airbag. Now run your crash test dummy into the wall again.


The Science Behind It

Isaac Newton was a man of incredible genius. He studied motion, gravity, energy, light, math, and chemistry. His three laws of motion serve as the cornerstone of modern day physics. This Crash Test Dummy experiment can teach you about his first law of motion.

Newton's first law of motion states that a body at rest will stay at rest and a body in motion will stay in motion, unless acted upon by an unbalanced force. When the car runs into the wall in Step 1, your action figure keeps going. When the dummy finally hits the wall, it encounters an unbalanced force, and it stops. Ouch! In Step 2, the rubber band (seat belt) provides the unbalanced force and the figure stops with the car.

When you wear a seatbelt in a car, the seatbelt stops you when the car stops during normal driving. An airbag will further help your body stop in a car crash, though your car's airbag does not taste like a marshmallow. Seat belts and airbags have saved countless lives over the years.


Rolling Uphill

Use two funnels to create another design that defies gravity.


From the Junk Drawer:

[] 2 small funnels

[] Tape

[] 2 wooden boards

[] A few books


Step 1: Place two funnels together with the large openings facing each other, then tape them together as shown.

Step 2: Stand two boards on their narrow edges. Place one end of each board on a book. One thick book is probably enough, or use several small books. Push the other two ends together so that the boards make a V. The wide part of the V should be equal to the width of the wide part of the two funnels.

Step 3: Place the two-funnel piece at the narrow part of the V and watch it roll uphill. You may need to experiment to get the height or angle of the boards just right. The picture is taken from above to help you see how to place the boards and funnel. After you have perfected the setup, share it with your friends, parents, and teacher. The activity is better viewed from the side, as this allows you to really see the funnels roll uphill.


The Science Behind It

The funnels have a center of gravity directly between the two wide openings of the funnels. The center of gravity is the point at which all mass is centered. When the funnels roll, the center of gravity is actually going down, as is expected. But the funnels' shape allows you to see the optical illusion of the funnels rolling uphill, even though the center of gravity actually rolls downhill.


Cork Accelerometer

Learn about acceleration with an old cork.

Adult supervision required


From the Junk Drawer:

[] Cork

[] Scissors

[] String

[] Hot glue gun

[] Empty clear plastic bottle with lid

[] Water


Step 1: Get assistance from an adult for the first three steps. First, use the point of a pair of scissors to create a small hole in the top of a cork that is small enough to fit inside your plastic bottle.

Step 2: Cut a piece of string slightly shorter than your empty plastic bottle. With adult help, use the hot glue gun to glue one end of the string into the hole in the cork.

Step 3: With adult help, use the hot glue gun to glue the other end of the string to the center of the inside of the bottle's lid. Let the glue dry completely.

Step 4: Take the wrapper off the clear plastic bottle. Fill the bottle with water. Leave less than ½ inch of air at the top.

Step 5: Do this step in the sink or on a surface that can get wet. Push the cork inside the bottle. Tightly screw on the lid (with the attached string). It is OK if some air is in the bottle.

Step 6: Turn the Cork Accelerometer upside down. Now walk around with the Cork Accelerometer. Hold it in front of you and pay attention to the cork. Take the Cork Accelerometer on your next car or bus ride. The cork will show you the direction of the acceleration. Did you see any movements that surprised you?


The Science Behind It

You are familiar with speedometers in cars — they measure speed. Accelerometers measure acceleration, the change in speed, although this accelerometer only gives you the direction of the acceleration. Objects accelerate whenever they experience an unbalanced force.

When you sit still, the forces on your body are equal. To accelerate, you need an extra unbalanced force. Pushing with your feet to start moving provides an unbalanced force. This unbalanced force gives you an acceleration that you can see with the cork. As you speed up, the cork goes forward. Positive acceleration is when you speed up.

When you are walking at a constant speed in a straight line, the cork will stay right in the middle of the water. You have zero acceleration, even though you are moving. Constant speed in a straight line means you have no unbalanced force. And no unbalanced force means zero acceleration.

You slow down because an unbalanced force acts against you. This is called deceleration. When you slow down, the cork will move in the direction opposite of the one in which you are moving. The cork shows you the direction of the unbalanced force (and the acceleration).

In the Cork Accelerometer, water also plays a valuable role. Water is denser than the cork. So a cork-sized amount of water has more mass. More mass equals more inertia, so the water wants to keep moving in the same direction it was originally. Since the water surrounds the cork, it provides a buoyant force that pushes on the cork and shows the direction of the unbalanced force. When you speed up, the water wants to stay still, so more water moves to the back of the jar, which pushes the cork forward (showing positive acceleration). As you slow down, the water wants to keep moving; more water moves to the front of the jar, which pushes the cork back (showing negative acceleration).

Accelerometers are commonly used inside game controllers and smart-phones. These accelerometers don't use water and a cork, but tiny chips made of silicon. By creating three tiny silicon accelerometers, they can tell up from down and sideways. These accelerometers are what tell the screen to flip on your smartphone. A similar device feels the acceleration in your game controller and sends commands to the gaming system.

Speeding up and slowing down takes an unbalanced force. So does turning a corner, but more on that in our next Junk Drawer Physics contraption.


Spinning Force Machine

Learn centripetal force with this homemade spinner.

Adult supervision required


From the Junk Drawer:

[] String

[] 2 fishing bobbers or corks

[] Hot glue

[] 2 empty plastic jars (mayonnaise or peanut butter jars work well) with lids

[] Water

[] Old paint stirrer or ruler

[] Lazy Susan (turntable)

[] Towel


Step 1: Use two pieces of string that are slightly shorter than the overall height of your jars. Tie the first piece of string to a fishing bobber or have an adult help you use hot glue to attach the string to a cork. You can use any two small floating objects. Now repeat for the other object with the second piece of string.

Step 2: Hot glue the free end of each string to the center of the inside of your jar lids. Let the hot glue dry before you go on to the next step. Always get adult help or permission to use a hot glue gun.

Step 3: Do this next step over a sink to save yourself some cleanup. Fill the jars completely full of water. Fill them until they start to overflow. Now push one cork or bobber into the water in each jar and tighten the lids. Turn the jars upside- down over the sink and check for leaks. Get an adult or older sibling to tighten the jar lids if they leak. Dry off the outside of the jars completely.

Step 4: Glue or tape a paint stirrer or ruler across the middle of a lazy Susan. You could also use a spinning office chair or an old record player if you have one, but skip the glue. I recommend paint stirrers, since most of us have several around the house, but an old ruler will also work. Hardware stores will give you a paint stirrer if you don't have one at home.

Step 5: Using hot glue, attach the jar lids to either end of the old ruler or paint stirrer. The jars should be upside-down. Allow the glue to cool completely.

Step 6: Before you spin the lazy Susan, which way do you think the bobbers will move? Now spin the turntable and watch the bobbers. Experiment with different speeds.


The Science Behind It

Objects naturally move in a straight line. For an object to curve, an unbalanced force must be applied. This unbalanced force is called centripetal force. It is always directed toward the center of a circle. The bobbers are free to move in any direction, but they go to the inside of the circle because of the centripetal force.

As the turntable spins faster, the bobbers lean more toward the center, since this centripetal force depends more on the speed than any other factor. The amount of force also depends upon the radius of the curve and the mass of the bobbers, but we didn't change those in this experiment. You could devise experiments to test those if you wanted to.

Water also plays a role in showing this centripetal force. The water and bobbers both want to keep moving in a straight line. Since the water is denser than the floating objects, it does a better job of moving straight, so water is pushed to the outside of the jars. More water outside the bobbers provides a buoyant force that pushes the bobber toward the center of the circle. The water helps to show you the direction of the centripetal force. When you ride in a car (or amusement ride) that turns a corner sharply, you feel something slightly different. You feel your body being pushed outward. That is because your body wants to continue in a straight line, but the car supplies an inward centripetal force through the seat and seat belts. Newton's third law of motion states that for every action there is an equal and opposite reaction. What you feel is a force equal to the car's centripetal force. But the force you feel is opposite in direction. Hence, our body senses an outward force.

Isaac Newton was born on Christmas day.


Paper Drop

Repeat Galileo Galilei's famous experiment in your own house.


From the Junk Drawer:

[] Scrap piece of paper

[] Any unbreakable object heavier than the paper


(Continues...)

Excerpted from Junk Drawer Physics by Bobby Mercer. Copyright © 2014 Bobby Mercer. Excerpted by permission of Chicago Review Press Incorporated.
All rights reserved. No part of this excerpt may be reproduced or reprinted without permission in writing from the publisher.
Excerpts are provided by Dial-A-Book Inc. solely for the personal use of visitors to this web site.

Table of Contents

Contents

Acknowledgments,
Introduction,
1 Forces and Motion,
2 Energy,
3 Sound and waves,
4 Light,
5 Electricity and Magnetism,
6 Fluids and Pressure,
Appendix,
Glossary,

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