Date: 05/20/2002 at 10:02:37 From: Blake Schelp Subject: Horse Power How is horsepower calculated?
Date: 05/20/2002 at 10:24:06 From: Doctor Sarah Subject: Re: Horse Power Hi Blake - thanks for writing to Dr. Math. From Russ Rowlett's _How Many? A Dictionary of Units of Measurement_: http://www.unc.edu/~rowlett/units/dictH.html#horsepower horsepower (hp) a unit of power representing the power exerted by a horse in pulling. The horsepower was defined by James Watt (1736-1819), the inventor of the steam engine, who determined after careful measurements that a horse is typically capable of a power rate of 550 foot-pounds per second. This means that a horse, harnessed to an appropriate machine, can lift 550 pounds at the rate of 1 foot per second. Today the SI unit of power is named for Watt, and one horsepower is equal to approximately 745.6999 watts. (In Britain this is rounded off to exactly 745.7 watts, and slightly different values are also used in certain industries.) Outside the U.S., the English word "horsepower" is often used to mean the metric horsepower, a slightly smaller unit. http://www.unc.edu/~rowlett/units/dictW.html#watt watt (W) the SI unit of power. Power is the rate at which work is done, or (equivalently) the rate at which energy is expended. One watt is equal to a power rate of one joule of work per second of time. This unit is used both in mechanics and in electricity, so it links the mechanical and electrical units to one another. In mechanical terms, one watt equals about 0.001 341 02 horsepower (hp) or 0.737 562 foot-pound per second (lbf/s). In electrical terms, one watt is the power produced by a current of one ampere flowing through an electric potential of one volt. The name of the unit honors James Watt (1736-1819), the British engineer who built the first practical steam engines. - Doctor Sarah, The Math Forum http://mathforum.org/dr.math/
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