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Hands-On Science

physics

Pop Rockets

Blast off! Launch your own rocket with just a few simple items.

Materials

  • Plastic 33mm film canisters with lids
  • Antacid tablet, like Alka-Seltzer
  • Water

Directions 

It's best to try this outside, or on a covered surface that's OK to get wet!

  1. Place one-quater to one-half a piece of an antacid tablet in the canister.
  2. Fill the canister one-third full with water. Snap the lid on tight.
  3. Shake the container, then put it down on a table. Step back, and watch what happens!

What's happening?

When water is added to the antacid tablet, many little bubbles of gas escape. The bubbles go up because they weigh less than water. When the bubbles reach the surface of the water, they break open. All the gas that escaped from the bubbles pushes on the sides of the canister.

When you blow up a balloon, the air makes the balloon stretch bigger and bigger. But the film canister can't stretch, and all the gas has to find somewhere to go. Eventually something has to give! That's why the canister pops its top, letting all the air and water rush out and pushing the lid up and up.

Real rockets work the same way, but using rocket fuel instead of tablets that fizz in water.