An engine is a machine that produces mechanical force and motion from another form of energy (e.g. a fuel source, compressed air, or electricity). It is also referred to as a prime mover. An automobile makes use of several motors to start the car and drive the car's various pumps but the power plant that propels the car is called an engine. The term motor was originally used to distinguish the new internal combustion engine-powered vehicles from earlier vehicles powered by a steam engine, such as the steam roller and motor roller; but can be used to refer to any engine that creates motion. Historic military siege engines included large catapults, trebuchets, and battering rams.