Work energy, power and machines
Energy is the ability to do work. The unit of energy is the joule. Potential energy is the type of mechanical energy that a body possesses by virtue of its position; a typical example is water held in a reservoir which is used to drive water turbines for the generation of electricity. The energy that drives the engine is derived from the chemical energy that is stored in the fuel. The chemical energy is converted into heat by the combustion process. Since energy is the capacity of a body to do work any change in the energy content of a body is accounted for by either work done on the body or work done by the body. Kinetic energy is the energy that an object possesses by virtue of its velocity.