Editing Horsepower (section)

==History==
[[File:6 horse team East Lampeter TWP LanCo PA 1.jpg|thumb|A team of six horses mowing hay in [[East Lampeter Township, Pennsylvania]], U.S.]]

The development of the [[steam engine]] provided a reason to compare the output of horses with that of the engines that could replace them. In 1702, [[Thomas Savery]] wrote in ''The Miner's Friend'':<ref>{{Cite web |url=http://www.history.rochester.edu/steam/savery/ |publisher=University of Rochester History Department |archive-url=https://web.archive.org/web/20090511121051/http://www.history.rochester.edu/steam/savery |archive-date=May 11, 2009 |title=The Miner's Friend |access-date=July 21, 2011 }}</ref>

:So that an engine which will raise as much water as two horses, working together at one time in such a work, can do, and for which there must be constantly kept ten or twelve horses for doing the same. Then I say, such an engine may be made large enough to do the work required in employing eight, ten, fifteen, or twenty horses to be constantly maintained and kept for doing such a work...

The idea was later used by [[James Watt]] to help market the [[Watt steam engine]], an improved [[Newcomen steam engine]]. He had previously agreed to take royalties of one-third of the savings in coal from the older Newcomen steam engines.<ref>{{Cite web |url= http://www.pballew.net/arithm17.html#hp |title= Math Words — horsepower |publisher= pballew.net |access-date= 2007-08-11 |archive-date= 2018-09-20 |archive-url= https://web.archive.org/web/20180920001001/http://www.pballew.net/arithm17.html#hp |url-status= usurped }}</ref> 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 [[Horse mill|mill wheel]] 144 times in an hour (or 2.4 times a minute).<ref name=Engineers121>Hart-Davis, Adam (2012). ''Engineers''. Dorling Kindersley. p. 121.</ref> The wheel was {{convert|12|ft}} in radius; therefore, the horse travelled {{nowrap|2.4 × 2π × 12}} feet in one minute. Watt judged that the horse could pull with a [[force]] of {{convert|180|lbf}}.<ref>{{cite book |title=James Watt: Craftsman and Engineer |first=H. W. |last=Dickenson |publisher=Cambridge University Press |year=2010 |isbn=9781108012232 |page=145 |quote=... based his calculations on data supplied to him to the effect that a mill horse walks, in a path of 24 ft. diameter, {{sfrac|2|1|2}} turns in a minute. Watt assumed that the mill horse exerted a pull of 180 lb.—we do not know where he got this figure—and found that it exerts 32,400 lb. per minute. By the following year he has rounded off the figure to 33,000, doubtless for ease in calculation.}}</ref> So:

:<math qid=Q120634922> P = \frac{W}{t} = \frac{Fd}{t} = \frac{180~\text{lbf} \times 2.4 \times 2\,\pi \times 12~\text{ft}}{1~\text{min}} = 32{,}572~\frac{\text{ft} \cdot \text{lbf}}{\text{min}}.</math>

''Engineering in History'' recounts that [[John Smeaton]] initially estimated that a horse could produce {{convert|22,916|ftlb}} per minute.<ref name="kirby-p171"/> [[John Theophilus Desaguliers|John Desaguliers]] had previously suggested {{convert|44,000|ftlb|0}} per minute, and [[Thomas Tredgold]] suggested {{convert|27,500|ftlb|0}} per minute. "Watt found by experiment in 1782 that a '[[Draft horse|brewery horse]]' could produce {{convert|32,400|ftlb|disp=sqbr|0}} per minute."<ref name="kirby-p171"/> James Watt and [[Matthew Boulton]] standardized that figure at {{convert|33,000|ftlb|0}} per minute the next year.<ref name="kirby-p171">{{Cite book |url=https://books.google.com/books?id=MXNtDQAAQBAJ&pg=PA171 |title=Engineering in History |first=Richard Shelton |last=Kirby |publisher=Dover Publications |page=171 |date=August 1, 1990 |isbn=0-486-26412-2 |access-date=June 13, 2018 }}</ref>

A common legend states that the unit was created when one of Watt's first customers, a brewer, specifically demanded an engine that would match a horse, and chose the strongest horse he had and driving it to the limit. In that legend, Watt accepted the challenge and built a machine that was actually even stronger than the figure achieved by the brewer, and the output of that machine became the horsepower.<ref>{{cite magazine |magazine=[[Popular Mechanics]] |url={{Google books|id=_d0DAAAAMBAJ|page=394|plain-url=yes}} |title=Motorcycle equipped with wireless |date=September 1912 |page=394}}</ref>

In 1993, R. D. Stevenson and R. J. Wassersug published correspondence in ''[[Nature (journal)|Nature]]'' summarizing measurements and calculations of peak and sustained work rates of a horse.<ref name="nature">{{Cite journal |last1=Stevenson |first1=R. D. |last2=Wassersug |first2=R. J. |year=1993 |title=Horsepower from a horse |journal=[[Nature (journal)|Nature]] |volume=364 |issue=6434 |page=195 |doi=10.1038/364195a0|pmid=8321316 |bibcode=1993Natur.364..195S |s2cid=23314938 |doi-access=free }}</ref> Citing measurements made at the 1925 [[Iowa State Fair]], they reported that the peak power over a few seconds has been measured to be as high as {{convert|14.88|hp|kW|abbr=on}}<ref>{{cite journal|last1=Collins|first1=E. V.|last2=Caine|first2=A. B.|year=1926|title=Testing Draft Horses|url=https://lib.dr.iastate.edu/bulletin/vol20/iss240/1|url-status=live|journal=Iowa Agricultural Experiment Station Bulletin|volume=240|pages=193–223|archive-url=https://web.archive.org/web/20200607104620/https://lib.dr.iastate.edu/bulletin/vol20/iss240/1/|archive-date=2020-06-07|access-date=2021-09-06}}</ref> and also observed that for sustained activity, a work rate of about {{convert|1|hp|kW|abbr=on}} per horse is consistent with agricultural advice from both the 19th and 20th centuries and also consistent with a work rate of about four times the [[basal rate]] expended by other vertebrates for sustained activity.<ref name="nature" />

When considering [[Human power|human-powered equipment]], a healthy human can produce about {{convert|1.2|hp|kW|abbr=on}} briefly (see [[orders of magnitude (power)|orders of magnitude]]) and sustain about {{convert|0.1|hp|kW|abbr=on}} indefinitely; trained athletes can manage up to about {{convert|2.5|hp|kW|abbr=on}} briefly<ref>Eugene A. Avallone et al., (ed), ''Marks' Standard Handbook for Mechanical Engineers 11th Edition '', Mc-Graw Hill, New York 2007, {{ISBN|0-07-142867-4}}, page 9-4.</ref>
and {{convert|0.35|hp|kW|abbr=on}} for a period of several hours.<ref>{{cite journal |last1=Ebert |first1=T. R. |title=Power output during a professional men's road-cycling tour |journal=International Journal of Sports Physiology and Performance |volume=1 |issue=4 |date=Dec 2006 |pages=324–325 |pmid=19124890|doi=10.1123/ijspp.1.4.324 |s2cid=13301088 }}</ref> The Jamaican sprinter [[Usain Bolt]] produced a maximum of {{convert|3.5|hp|kW|abbr=on}} 0.89 seconds into his 9.58 second {{convert|100|m|yd|1|adj=on}} sprint world record in 2009.<ref>{{cite web |title=Scientists Model "Extraordinary" Performance of Bolt |url=http://www.iop.org/news/13/jul/page_60709.html |publisher=Institute of Physics |date=26 July 2013 |archive-url=https://web.archive.org/web/20160309194600/http://www.iop.org/news/13/jul/page_60709.html |archive-date=9 March 2016 |access-date=15 December 2023 }}</ref>{{Failed verification|date=December 2023}}

In 2023 a group of engineers modified a [[dynamometer]] to be able to measure how much power a horse can produce. This horse was measured to {{convert|5.7|hp|kW|abbr=on}}.<ref>{{Cite AV media |publisher=Donut |title=How Much Horsepower is a Horse? |date=24 November 2023 |url=https://www.youtube.com/watch?v=7qxTKtlvaVE&ab_channel=Donut |access-date=30 November 2023 |via=YouTube }}</ref>