3.6

## University of Liverpool

Skip to 0 minutes and 12 secondsThis makes for an exciting spectacle, but how does it work? Where does the energy come from to lift this guy out of the water? He is attached to the Jet Ski by a hose pipe and the Jet Ski has an engine. The engine turns an impeller in a tube under the Jet Ski. The impeller sucks water in one end of the tube and squirts it out the other. In this case, the hose pipe is attached to the exit from the tube. If we were studying mechanics, we would talk about Newton's third law, for every action there is an equal and opposite reaction.

Skip to 0 minutes and 57 secondsSo, as the water is squirted out in one direction, there is an equal force in the opposite direction, which keeps the man in the air. At the fundamental level, this is the same as the hair dryer and the jet engine that I talked about in this week's introduction. But, as I said before, this is a thermodynamics course and I would like to think about it in terms of energy and mass flow. Let's look at the connection between energy and mass.