For you to demonstrate outside but a huge hit in our house- the AlkaSeltzer rocket! Use a film canister (hard to find- ask a film counter!) and a half tablet of alka seltzer. Put the tablet in the container and a few drops of water on the lid. Put the container on the lid, lid side down and stand back and wait. If you get it tight, the container will launch 8-10 feet up with a POP!