Prime mover

(anatomy) A muscle that produces a specific motion or maintains a specific posture.
(mechanical engineering) The component of a power plant that transforms energy from the thermal or the pressure form to the mechanical form. A tractor or truck, usually with four-wheel drive, used for hauling tasks.

The component of a power plant that transforms energy from the thermal or the pressure form to the mechanical form. Mechanical energy may be in the form of a rotating or a reciprocating shaft, or a jet for thrust or propulsion. The prime mover is frequently called an engine or turbine and is represented by such machines as waterwheels, hydraulic turbines, steam engines, steam turbines, windmills, gas turbines, internal combustion engines, and jet engines. These prime movers operate by either of two principles: (1) balanced expansion, positive displacement, intermittent flow of a working fluid into and out of a piston and cylinder mechanism so that by pressure difference on the opposite sides of the piston, or its equivalent, there is relative motion of the machine parts; or (2) free continuous flow through a nozzle where fluid acceleration in a jet (and vane) mechanism gives relative motion to the machine parts by impulse, reaction, or both. See also Gas turbine; Hydraulic turbine; Impulse turbine; Internal combustion engine; Power plant; Reaction turbine; Steam engine; Steam turbine; Turbine.