Horsepower
. Horsepower, unit of power in the English system, for measuring the rate at which an engine or other prime mover can perform mechanical work. It is usually abbreviated hp. Its electrical equivalent is 746 watts, and the heat equivalent is 2545 British thermal units per hour. One horsepower was originally defined as the amount of power required to lift 33,000 pounds 1 foot in 1 minute, or 550 foot-pounds per second. Scottish engineer and inventor James Watt established this value for the horsepower after determining in practical tests that horses could haul coal at the average rate of 22,000 foot-pounds per minute. He then arbitrarily raised this figure by a factor of one-half to establish the current value. In the metric system, 1 horsepower is sometimes called force de cheval or cheval-vapeur and is defined as 4500 kilogram-meters per minute, which is equivalent to 32,549 foot-pounds per minute, or 0.986 of the English horsepower unit. Three different horsepower values are used to qu