A small cannon that fires a plastic film canister is one way to start a lesson off with a bang, well not really a bang, more like a pop. It shoots a film canister about 25 feet and is powered by just two drops of alcohol. The basic idea can be shown very simply, or with some time and effort can be built into a nice addition for an adult's homemade science toy demonstration piece.
Warning: while the amount of fuel used is very small, it still produces a small explosion and flame, proper supervision and precautions are strongly recommended. NOT SUGGESTED FOR CHILDREN