Horse power is an interesting thing, with horses, but especially cars and trucks.

Horse power is an interesting thing, with horses, but especially cars and trucks. According to the The American Heritage® Dictionary of the English Language, Fourth Edition Copyright © 2004, the definition of horse power is:

1. (Abbr. hp) A unit of power in the U.S. Customary System, equal to 745.7 watts or 33,000 foot-pounds per minute.
2. The power exerted by a horse in pulling.
3. Informal. Effective strength: political horsepower; computer horsepower.

Where Did the Term “Horsepower” Come From?

James Watt invented the term “horsepower” to help market his improved steam engine. He had beforehand agreed to acquire royalties of 1/3 of the savings in coal from the older Newcomen steam engines. This royalty system did not work with customers who did not have steam engines, but used horses in its place. Watt determined that a horse could turn a mill wheel 144 times in an hour (or 2.4 times a minute). The wheel was 12 feet in radius, thus in a minute the horse traveled 2.4 × 2π × 12 feet. Watt judged that the horse could pull with a force of 180 pounds (just assuming that the measurements of mass were equivalent to measurements of force in pounds-force, which were not well-defined units at the time). So:

Engine horsepower

The power of an engine is measured or estimated at several points in the transmission of the power from its generation to its application. The more horsepower an engine has, the faster is can accelerate. This is extremely important for auto racers of all kinds. Horsepower can be manipulated in many ways, including adding horsepower by several methods such as something as simple as lightening the overall weight of the vehicle.