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Difference between revisions of "Horsepower"
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==Definition== | ==Definition== | ||
There have been many definitions for the term over the years since James Watt first coined the term in 1782. The following metrics have been widely used: | There have been many definitions for the term over the years since James Watt first coined the term in 1782. The following metrics have been widely used: | ||
* [[#Mechanical horsepower|Mechanical horsepower]] — 0.74569987158227022 | * [[#Mechanical horsepower|Mechanical horsepower]] — 0.74569987158227022 kW](33,000 ft·lbf per minute) | ||
* [[#Metric horsepower|Metric horsepower]] — 0.73549875 kW | * [[#Metric horsepower|Metric horsepower]] — 0.73549875 kW | ||
* [[#Electrical horsepower|Electrical horsepower]] — 0.746 kW | * [[#Electrical horsepower|Electrical horsepower]] — 0.746 kW | ||
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== History of the term "horsepower" == | == History of the term "horsepower" == | ||
The term "horsepower" was invented by James Watt to help market his improved steam engine. He had previously agreed to take royalties of one third of the savings in coal from the older Newcomen steam engines[http://www.pballew.net/arithm17.html]. This royalty scheme did not work with customers who did not have existing steam engines but used horses instead. 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 travelled 2.4 × 2π × 12 feet. Watt judged that the horse could pull with a | The term "horsepower" was invented by James Watt to help market his improved steam engine. He had previously agreed to take royalties of one third of the savings in coal from the older Newcomen steam engines[http://www.pballew.net/arithm17.html]. This royalty scheme did not work with customers who did not have existing steam engines but used horses instead. 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 travelled 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: | ||
:<math> power = \frac{work}{time} = \frac{force \times distance}{time} = \frac{(180 \mbox{ lbf})(2.4 \times 2 \pi \times 12 \mbox{ ft})}{1\ \mbox{min}}=32,572 \frac{\mbox{ft} \cdot \mbox{lbf}}{\mbox{min}}</math> | :<math> power = \frac{work}{time} = \frac{force \times distance}{time} = \frac{(180 \mbox{ lbf})(2.4 \times 2 \pi \times 12 \mbox{ ft})}{1\ \mbox{min}}=32,572 \frac{\mbox{ft} \cdot \mbox{lbf}}{\mbox{min}}</math> | ||
This was rounded to an even 33,000 ft·lbf/min[http://sections.asme.org/Philadelphia/sept02.htm]. | This was rounded to an even 33,000 ft·lbf/min[http://sections.asme.org/Philadelphia/sept02.htm]. | ||