Film Canister Rocket
What To Do
Take a trip to your local photo shop and ask if they have any spare film canisters! The ones with a lid that clips inside rather than outside work much better (these tend to be white in colour). You will also need some Alka-Seltzer tablets so pop into your local grocery shop or chemist on your way back.
Fill the film canister about half full with water, you can experiment with more or less water after your first successful launch. It is best to launch your rocket outside to avoid damage or getting your carpet wet. Place one Alka-Seltzer tablet inside the canister, snap the lid on, turn it upside down and put it on the floor (or other stable flat surface). As soon as it is set, move back to a safe distance, about 3 metres should be enough. Now wait! It may take anything from 15-30 seconds for your rocket to launch If it fails, ask a grown up to help check it is ok.
As soon as the Alka-Seltzer tablet and the water mix, they start making a gas known as carbon dioxide. With the lid firmly in place, the gas cannot escape so it starts to build up inside the canister. The build up of pressure causes a force to push against the inside of the canister in all directions. For a while nothing seems to happen but eventually the pressure builds up so much that the lid is popped off. With the lid gone, there is nothing for the downward force to push against so the upward force is unbalanced causing it to push the rocket up into the sky.