The vortex cannon provides hours of fun. The smoke allows one to visualize the associated fluid dynamics. The toroidal rings are remarkably stable and travel distances on the order of 20 - 30 feet with full strength. A nice demo is to setup the cannon and place a candle at the other end of the room. Then use the cannon to blow out the candle as if by magic (without using the fog). Then add the fog so everyone can see what is happening.