You will need:
Generic Alka Seltzer tablets (cheap is good)
35 mm film canisters (Fuji cans works best)
water in paper cups
The activity involves breaking up the Seltzer tablets, putting them in the film canisters and putting in a little water. Snap the lid shut and wait….
The seltzer will fizz and pop off the lid with a loud noise. Make sure the canister is being held pointing away from faces and other people. Make the activity more of a science experiment by allowing the kids to experiment with different amounts of seltzer and water to determine the best ratio of ingredients. Finally, have a “pop-off” where the kids attempt to get the longest distance from their lid when it pops off. Have the kids make markers to show how far their lids have gone, so you can see who achieve the greatest distance.
This activity works well as singles or in pairs. Water will get onto the floor, so avoid doing this in carpeted areas. Also, drying off the lip of the lids and the canister between experiments helps prevent premature popoff.