Horsepower

Horsepower is the unit of energy needed to lift 550 pounds (249 kilograms) the distance of 1 foot (.305 meters) in 1 second. Near the end of the eighteenth century, Scottish engineer James Watt (1736-1819) sought to compare the rate at which the steam engine and horses could pump water out of coal mines. In order to define a "horsepower," he tested horses and concluded that a strong horse could lift 150 pounds (68 kilograms) the distance of 220 feet (67 meters) in 1 minute. Therefore, 1 horsepower was equal to 150 x220/1minute, or 33,000 foot pounds per minute (4,556 meter kilograms per minute).

The term horsepower was frequently used in the early days of the automobile because the "horseless carriage" (as it was called) was constantly being compared to the horse-drawn carriage.