This power terminology-confusion will apparently not go away for another generation or two. I am going to try to summarize what we know and what we mostly agree on.
We know that POWER is an *alternate* term for ENERGY per TIME just as SPEED is an *alternate* term for DISTANCE per TIME. So are other quantities and their units similarly formed. Power is unique in the sense that its energy per time form has several “shorthands units" such as hp, PS, kun, .... and, of course, the W that coexists with any number of energy units per any number of time units. Since James Watt’s achievement, the briefer hp, PS, kun, thermal hp, .... has been the preferred form of the 'energy per time unit' in applications for pumps, horses, steam and IC engines, electricity generating plants, etc. Elsewhere, the power unit has been retained in the energy per time form, such as the nutritional cal/day. The distinction between "power" and "energy" in a statement is often unclear; one needs to know whether the info refers to just energy alone or to energy per time. For example, saying “the energy consumption in 2007 was 100 EJ” clearly implies power. If it had been written appropriately as 100 EJ/a (or EJ/y, or W) it would be unambiguous. Similarly, it would be clear if written as 274 PJ/d, or x Cal/hr, or x EJ/eternity. Obviously unifying the world on W (i.e. J/s) introduced a great simplification, that, however, is still not appreciated everywhere such as with the mentioned nutrition data. On a related subject, any energy unit, SI or not, is "never" standing alone. It is always per something: time, volume, mass, serving, etc. But unlike energy per time, the other “energies per whatever" do not have the alternative “shorthand” unit such as for the massic energy density, or volumic energy density. Notice that the nutrition DV (daily value) is a human power; its unit is J/(day-person), i.e. proportional to W/person. Stan J. On Wed, Oct 28, 2020 at 11:26 PM Peter Goodyear <[email protected]> wrote: > Hello, everyone, > > Thanks for posting this to the mailing list, Ezra. I’ve re-posted the > YouTube link to Reddit’s Metric forum. Comments, if any, will be here: > https://nam01.safelinks.protection.outlook.com/?url=https%3A%2F%2Fwww.reddit.com%2Fr%2FMetric%2Fcomments%2Fjk17f1%2Fvideo_explaining_horsepower_ends_by_showing_how%2F&data=04%7C01%7Cusma%40lists.colostate.edu%7C3b88c2b9433a44466bf508d87c208ee4%7Cafb58802ff7a4bb1ab21367ff2ecfc8b%7C0%7C1%7C637395826566346484%7CUnknown%7CTWFpbGZsb3d8eyJWIjoiMC4wLjAwMDAiLCJQIjoiV2luMzIiLCJBTiI6Ik1haWwiLCJXVCI6Mn0%3D%7C2000&sdata=7vpS%2FxRPk6VIpdA38u3Rg%2BoLWrIHRUfMTve7DoYoFdg%3D&reserved=0 > <https://nam01.safelinks.protection.outlook.com/?url=https%3A%2F%2Fwww.reddit.com%2Fr%2FMetric%2Fcomments%2Fjk17f1%2Fvideo_explaining_horsepower_ends_by_showing_how%2F&data=04%7C01%7Cusma%40lists.colostate.edu%7C3b88c2b9433a44466bf508d87c208ee4%7Cafb58802ff7a4bb1ab21367ff2ecfc8b%7C0%7C1%7C637395826566346484%7CUnknown%7CTWFpbGZsb3d8eyJWIjoiMC4wLjAwMDAiLCJQIjoiV2luMzIiLCJBTiI6Ik1haWwiLCJXVCI6Mn0%3D%7C2000&sdata=7vpS%2FxRPk6VIpdA38u3Rg%2BoLWrIHRUfMTve7DoYoFdg%3D&reserved=0> > > Many thanks, > > Peter Goodyear, > > Melbourne, Australia > e-mail: [email protected] > > = = = = = = = = = = = = = = = = = = = = = = = = = = = = > > On 29 Oct 2020, at 12:00, John Steele <[email protected]> wrote: > > Horses are terrible engines. Maximum torque at 2.5 RPM. > > On Wednesday, October 28, 2020, 05:36:02 PM EDT, Ezra Steinberg < > [email protected]> wrote: > > > This guy on YouTube does great videos on cars and engineering of cars. > > But this one on horsepower is well done and ends by finally saying that > the "watt" is the correct unit to use. What a finish! > > https://nam01.safelinks.protection.outlook.com/?url=https%3A%2F%2Fyoutu.be%2FgC2-JKO0c2I&data=04%7C01%7Cusma%40lists.colostate.edu%7C3b88c2b9433a44466bf508d87c208ee4%7Cafb58802ff7a4bb1ab21367ff2ecfc8b%7C0%7C1%7C637395826566356480%7CUnknown%7CTWFpbGZsb3d8eyJWIjoiMC4wLjAwMDAiLCJQIjoiV2luMzIiLCJBTiI6Ik1haWwiLCJXVCI6Mn0%3D%7C2000&sdata=RIAj77fe6yjhQfoMhw6Ql5DBsBCvC7YnlmvWJykOMJg%3D&reserved=0 > <https://nam01.safelinks.protection.outlook.com/?url=https%3A%2F%2Fyoutu.be%2FgC2-JKO0c2I&data=04%7C01%7Cusma%40lists.colostate.edu%7C3b88c2b9433a44466bf508d87c208ee4%7Cafb58802ff7a4bb1ab21367ff2ecfc8b%7C0%7C1%7C637395826566356480%7CUnknown%7CTWFpbGZsb3d8eyJWIjoiMC4wLjAwMDAiLCJQIjoiV2luMzIiLCJBTiI6Ik1haWwiLCJXVCI6Mn0%3D%7C2000&sdata=RIAj77fe6yjhQfoMhw6Ql5DBsBCvC7YnlmvWJykOMJg%3D&reserved=0> > > Ezra > > _______________________________________________ > USMA mailing list > [email protected] > https://lists.colostate.edu/cgi-bin/mailman/listinfo/usma > _______________________________________________ > USMA mailing list > [email protected] > https://lists.colostate.edu/cgi-bin/mailman/listinfo/usma > > _______________________________________________ > USMA mailing list > [email protected] > https://lists.colostate.edu/cgi-bin/mailman/listinfo/usma >
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