Potato Cannon!

Who says you can't play with your food? It's okay when it's in the name of science! Shock your kids by instigating a food fight. The target? The great outdoors. The ammunition? The humble potato. With preparation, and a little help from Boyle's Law, the potato will go "ballistic”—literally!

This experiment is an explosive demonstration of the basic principle of Boyle's Law: as pressure increases, volume decreases. Scientifically stated, this means: “Under constant temperature, the volume of a gas is inversely proportional to the total amount of pressure applied.” In this experiment, the gas is the air inside the pipe, lodged between the two potato plugs. When the broomstick is shoved into the pipe, one plug is pushed toward the other. This suddenly reduces the volume of the gas, thereby increasing its pressure. The burst of pressure sends the potato plug flying.

Elapsed time: 1 hour

What You Need:

• 2 sets of goggles (one for you and one for your child)
• 2 potatoes
• 4' length of PVC pipe (1" diameter), available at most hardware stores
• 5' wooden broomstick (diameter narrower than that of the tube)
• Rubber stopper (optional)

What to Do:

1. Have your child press one end of the pipe down into a potato, so that a plug of potato becomes lodged in the end. Then have her do this with her other potato and the other end of the pipe, so that she has a potato plug at each end.
2. Put on your goggles and have her do the same. Ask her to hold the pipe with one hand and point it away from both of you, as well as anything breakable.
3. Have her position the broomstick at the closer end of the pipe, just touching the potato plug (if the broomstick is much narrower than the pipe, add a rubber stopper to the end touching the potato).
4. Help her edge the broomstick slowly through the pipe, pushing one potato plug toward the other. Ask her to stop when she is about a third of the way down, and then pull the broomstick back.
5. Finally, ask her to ram the broomstick back into the pipe very quickly. The plug at the far (“barrel”) end will shoot out with great force.

Take care! Make sure the potato gun is not pointed in the direction of anyone watching, china, or other breakables. All things considered, it's safer to perform this experiment outside in a wide, open space.