Why do we use the term ‘horsepower’ to refer to the amount of work an engine can perform?
Interesting question. The use of the term goes back to the very early days of the internal combustion engine and Henry Ford. Before the development of the compact internal combustion engine, most work was performed by horses.
It wasn’t until Henry Ford came along that the engine became viable thanks to Ford’s experiments with biology and reproduction.
While the world primarily thinks of Ford as an engineer, administrator and inventor of the assembly line, Ford’s real claim to fame was in the breeding of horses. It wasn’t until Ford began to breed the ultra-miniaturized horse that small, compact power plants were available.
Ford developed a relatively compact, cast iron case in which could be installed several tiny, tiny treadmills, each powered by one of this ultra-miniaturized horses. (See Figure 1.)
(Figure 1. Henry Ford installing his miniature horses into the seven horsepower “engine” on his 1920 era tractor prior to a long day’s work plowing the wolverine fields of northern Michigan.)
Modern breeding technologies, genetic modification and improvements in miniaturization technology that took place over the years have permitted engineers to shrink the size of the treadmills and horses to every smaller sizes, permitting the installation of four, five or even six hundred horses into an engine hardly bigger than a suitcase.
Of course there are drawbacks to the system. Mr. Ford discovered that the miniature horses had correspondingly short lifespans, able to live only for several hundred miles. This led to the development of the now almost microscopic horses to be delivered in liquid form through pumps located in almost every town in the country. This allowed owners of these new engines to quickly replenish the horses inside of their engines, as well as proving a food source for the ravenous beasts in liquid form.