A mini-rocket that uses water and carbon dioxide as "fuel". The principle of the rocket is simple; the Newton third law of motion states "for every action there is an equal opposite reaction". The action is the gas produced by the effervescent when is in contact with water. The gas creates pressure and accumulates until the cap pops out. As the cap have no where to go, the plastic can goes up (the opposite reaction) because the gas pushes it.
http://www.josepino.com/other_projects/index?rocket.jpc