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This week's LabZone activity
Oct. 8, 2003
Make a Frictionless Toy Air Car
You can build a frictionless toy air car from plywood, an empty thread spool, and a 12-inch balloon.
Things you will need:
- 1/4-in. plywood
- empty thread spool, or cork, cork borer, and glue
- 12-in. balloon
- saw
- ruler
- an adult
- drill and bit (1/16-in.)
- sandpaper
- smooth, level surface
- thin pieces of wood or newspapers
- table that has a smooth surface, or a long, smooth board
- carpenter's level
What to do:
Ask an adult to help you build the car. You will need a square piece of 1/4-in. plywood 7.5 centimeters (3 inches) on a side. The plywood should be smooth on both sides. If the lower side of the wood square is not perfectly smooth, use some sandpaper to make it so.
Ask an adult to drill a hole 1.5 millimeters (1/16 in.) in diameter through the exact center of the wood square. An empty thread spool can then be glued to the center of the square. Alternatively, you can bore a hole through a cork and glue it to the wood square. In either case, be sure the hole through the spool or cork is in line with the hole that was drilled through the wood square.
Place the air car on a very smooth, level surface, such as a kitchen or laboratory counter. Blow up a balloon and attach it to the spool as shown in the drawing (below). Release the neck of the balloon so air can flow through the spool and the hole in the square. The air will lift the car slightly, providing a nearly frictionless surface on which the air car can move.
Give the car a gentle push. It should move at what appears to be constant speed along the smooth, level surface. If it does not, you may need to sand the lower surface of the wood again; you may need a stronger balloon to force more air through the hole; or you may need to make the hole bigger by using a slightly larger drill bit than the one you used before.
What happens to the car when all the air has left the balloon?
Fill the balloon again and give the toy air car a push along a smooth, level surface. What do you notice about the car's speed if you give it a stronger push? A weaker push?
You know that if you drop your toy car or anything else, it will fall because the earth's gravity pulls everything toward its center. Similarly, a ball placed on even a slight incline will roll because the force of gravity pulls it closer to the earth.
You car is an excellent gravity detector. To see this for yourself, inflate the car's balloon and place the car on an incline. To make a slight incline, put thin pieces of wood or newspapers under two legs of a level table that has a smooth surface. You can do the same thing with a long, smooth board.
What happens when you place your air car at the top of the incline and let go? Why do you think the car moves faster and faster as it slides down the incline?
What happens to the way the car moves if you make the incline steeper? If you make it less steep?
How can you use your air car to tell whether a kitchen counter, a table, or a smooth floor is level?
Exploring on your own:
Design and carry out experiments involving motion and colliding pucks on an air-hockey game.
As a thought experiment, suppose you were on board the space shuttle in orbit about the earth. Why would you not need a balloon to make the car move along a straight line along the shuttle at a constant speed?
As another thought experiment, what would happen if you placed your air car on a smooth, inclined board in the space shuttle? Would it move if you did not push it? How would it move if you did push it along the incline?
Reproduced with permission from Science Projects About the Physics of Toys and Games by Robert Gardner. Copyright © 2000 by Enslow Publishers (www.enslow.com/).
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