Tennis ball cannon on cart (2nd & 3rd Law)
This home-made cannon can be set on the floor for a dramatic demo. It is safe, but the tennis ball travels very fast and quite far. The cannon is on wheels so students can see the relative speed of the ball and cannon due to their different masses. Everything you need is in the cannon barrel. Use the stick to push the tennis ball down the barrel as far as it will go. Place 2 only, small squirts of fuel into the small hole in the rear of the cannon. Lift the cannon and rotate it around to have the fuel "coat" the inside of the firing chamber. Blow a couple of puffs of air into the fuel hole to mix oxygen with the fuel. Place it on the floor so that the ball and cannon can travel in a straight path with enough room in front of the class (never aim near people). Stick a lighted match to the top of the fuel hole and "look out"!! The tennis ball launches with a "whoosh".