Motive power is a term in thermodynamics referring to the harnessed energy or force that is used to power a mechanical device or system. Most simply, it's any source of power that imparts motion. Motive power is expressed mathematically as force X distance.
Motive power, as a concept, can be described as that which provides power to a system. The term motive power is most often used in science and engineering industries. Water, steam and wind are a few of the natural agents that provide motive power. Examples for water as a motive power include waterwheels, devices used to harvest tidal power and rain-powered solar panels. Steam pressure is used to move machinery and store power through pressure vessels and piston systems such as in locomotive engines. Wind turbines generate electricity and are a well-known example of motive power.
The use of power to power a mechanical system can be dated back to 1711 with the Newcomen engine, which moved buckets of water out of a well vertically. This engine created enough power to replace a team of 500 horses that had been used to pump water out of a mine. The Newcomen engine contributed significantly to the invention of the steam engine during the 18th century. The word motive derives from this movement, and lead to the standardized expression of engine motive power as horsepower as a comparison to the power of draft horses.