Horsepower
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Horsepower is the unit of power in the English system of measurement. The term horsepower was coined by James Watt (Watt) (1736-1819), the Scottish inventor and mechanical engineer renowned for his improvements of the steam engine.
Definition
One horsepower (hp) is equivalent to 0.7457 kW in standard SI units. A healthy human can sustain about 0.1 horsepower, a car can generate several hundred horsepower, while a steam turbine in an electric power plant can produce more than 1.5 million horsepower.
Horsepower-hour is a unit of energy or work equal to the work done by the applied power of one horsepower over the period of one hour. The corresponding standard SI unit of energy is the joule. One joule = 3.73·10-7horsepower-hour.
History
The term horsepower was coined by James Watt (1736-1819), the Scottish inventor and mechanical engineer renowned for his improvements of the steam engine. In the early 1780s, Watt and his partner Matthew Boulton set out to sell their steam engines to the breweries of London, calculating that they would be likely customers because brewing was such an energy-intensive process. In order to convince the breweries of the advantages of the steam engine, Watt needed a method to compare their capabilities relative to horses, the power source they were seeking to replace. The typical brewery horse, attached to a mill that ground the mash for making beer, walked in an endless circle with a 24-foot diameter, pulled with a force of 180 pounds, and traveled at a speed of 180.96 feet per minute. Watt multiplied the speed times the force and came up with 32,580 ft-lbs/minute. That was rounded off to 33,000 ft-lbs/minute, the figure used today.
A healthy human can sustain about 0.1 horsepower, a car can generate several hundred horsepower, while a steam turbine in an electric power plant can produce more than 1.5 million horsepower.
Conversions
| from / to | kilowatt-hour | electronvolt | Btu | horsepower hour |
foot-pound | ||||
|---|---|---|---|---|---|---|---|---|---|
|
1 Joule |
1 | 0.278 · 10?3 | 6.241 · 1018 | 0.2388 | 9.4782 · 10?4 | 3.7251 · 10-7 | 0.7376 | 1 · 107 | 9.4782 · 10?9 |
| 1 kilowatt-hour | 3.6 · 106 | 1000 | 22.5 · 1024 | 8.5985 · 105 | 3.4121 · 103 | 1.3410 | 2.6552 · 106 | 3.6 · 1013 | 0.0341 |
| 1 electronvolt | 0.1602 · 10?18 | 44.5 · 10?27 | 1 | 3.8267 · 10?20 | 1.5186 · 10?22 | 5.9682 · 10?26 | 1.1817 · 10?19 | 1.6022 · 10?12 | 1.5186 · 10?27 |
|
1 calorie |
4.1868 | 1.163 · 10?3 | 0.261 · 1018 | 1 | 3.9683 · 10?3 | 1.56 · 10?6 | 3.0880 | 4.186 · 107 | 3.9683 · 10?8 |
| 1 Btu | 1.055 · 103 | 0.293 | 6.585 · 1021 | 251.996 | 1 | 3.9302 · 10?4 | 778.169 | 1.05435 · 1010 | 1 · 10?5 |
| 1 horsepower-hour | 2.6845 · 106 | 745.60 | 1.6755 · 1025 | 6.4119 · 105 | 2.5444 · 103 | 1 | 1.98 · 106 | 2.6845 · 1013 | 2.5444 · 10-2 |
| 1 foot-pound | 1.3558 | 3.7662 · 10-4 | 8.4623 · 1018 | 0.3238 | 1.2851 · 10-3 | 5.0505 · 10-7 | 1 | 1.3558 · 107 | 1.2851 · 10-8 |
| 1 · 10-7 | 2.7778 · 10-11 | 6.2415 · 1011 | 2.4 · 10-8 | 9.4782 · 10-11 | 3.7251 · 10-14 | 7.4 · 10-8 | 1 | 9.4782 · 10-16 | |
|
1 therm |
1.0551 · 108 | 2.9307 · 104 | 6.5851 · 1026 | 2.520 · 107 | 1 · 105 | 39.301 | 7.7817 · 107 | 1.0551 · 1015 | 1 |
Further Reading
- How Many? A Dictionary of Units of Measurement, Russ Rowlett, Center for Mathematics and Science Education, University of North Carolina at Chapel Hill
- SI base units and SI derived units, the Physics Laboratory, National Institute of Standards and Technology
- Energy conversion tool at unitconversion.org.
