With 400 rubber bands and a large watermelon you can demonstrate the difference between potential and kinetic energy by exploding a watermelon with rubber bands. You probably want some goggles to protect your eyes. Place a bunch of rubber bands around the middle of the watermelon. Be careful though as all that pressure from the outsite will start to explode the watermelon. Rubber bands are a great example of potential energy. Potential energy is energy that is stored up, not being used, just waiting to be unleashed.