Horsepower and watts: how do they differ?

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HP versus WATT how do they differ?

Horsepower ( HP ) versus watts ( WATT ) 

The term “ horsepower ” or horsepower (hp) was introduced during Britain's Industrial Revolution, when horses provided power for machinery, by “ James Watt ” the celebrated scientist who improved steam engines until they became a driving force of the Industrial Revolution. " The term horsepower compares how much modern machinery can replace the work of animals such as horses.

Its origin is traced to James Watt improving Newcomen's steam engine. Watt asked for a royalty equivalent to 1 in 3 of the value of coal saved by his engine compared with a Newcomen engine.  

However, this rate could not be applied to people previously using horses rather than steam engines. Watt therefore calculated “ the power of a horse ” to determine royalties for these customers too.  

According to his calculation, a horse could turn a flour mill with a radius of 12 feet 144 times within 1 hour, equivalent to 2.4 revolutions per minute. Using power = work/time = (force x distance)/time gave 1 horsepower = ( 180 pounds)( 2.4x3.14x12 feet)/ 1 minute = 32,572 feet, or 33,000 foot-pounds per minute.  

Another account says Watt experimentally found that a pony could, on average, lift 220 pounds through 100 feet in 1 minute, working shifts of 4 hours. As a large horse was considered more powerful than a small one by 50% the resulting horsepower value was 1.5 x 100x 220 = 33,000 foot-pounds per minute.