If you were rich enough or your parents were lenient enough to let you have a trampoline when you were younger, you almost certainly attempted a double bounce. This occurs when two people bounce at the same time causing one to shoot much higher in the air and possibly shatter a collarbone. The double bounce is merely a case of conservation of energy. When two people jump on the elastic trampoline, their gravitational potential energy is converted into elastic potential energy in the trampoline. In order to get a good bounce, one of the participants must lift up their legs so as not to be in contact with the trampoline anymore. This will allow all the energy to be transferred to the remaining bouncer in the form of kinetic energy, which will send them much higher thus maximizing fun and injury risk.