# Talk:Horsepower

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## Original horse power

The original horsepower unit was selected to show potential buyers of the new steam engines how much they would save by switching from horses to steam. The horsepower unit represented the rate of work a horse could do on a continous basis (all day long). Thats why its only a small fraction of the maximum capability of a horse.

## Why is this entry flagged?

"This article or section may contain original research or unverified claims." How so?

## Confusing Formulae

Why do the equations for drawbar pull use expressions like v/mph instead of just 'v'? it makes the equations look much more complicated than they really are and I've not seen equations written like this before. Can someone who is good with an equation editor tidy them up? Stub Mandrel (talk) 18:11, 23 February 2015 (UTC)

Apparently, this way of describing mathematical relations is referred to as quantity calculus. Since I’ve just found quite a nice book (published by The Royal Society of Chemistry), I can recommend it to you as well: The 2nd and 3rdeditions have been made available online as PDF files.[1] I can provide below excerpts:

Quantity calculus is a system of algebra in which symbols are consistently used to represent physical quantities and not their numerical values expressed in certain units. Thus we always take the values of physical quantities to be the product of a numerical value and a unit, and we manipulate the symbols for physical quantities, numerical values, and units by the ordinary rules of algebra. This system is recommended for general use in science and technology. Quantity calculus has particular advantages in facilitating the problems of converting between different units and different systems of units.
...
A more appropriate name for "quantity calculus" might be "algebra of quantities", because the principles of algebra rather than calculus (in the sense of differential and integral calculus) are involved.
- Quantities, Units and Symbols in Physical Chemistry, 2007, p. 131

If it is desired to write the relationship between numerical values it should be written in the form:
${\displaystyle A/(S\ mol^{-1}\ cm^{2})={\frac {1000\ K/(S\ cm^{-1})}{c/(mol\ dm^{-3})}}}$
- Quantities, Units and Symbols in Physical Chemistry, 2007, p. 132

Quantity equations: Equations between quantities are used in preference to equations between numerical values, and symbols representing numerical values are different from symbols representing the corresponding quantities. When a numerical-value equation is used, it is properly written and the corresponding quantity equation is given where possible."
proper: (l/m) = 3.6-1 [v/(km/h)](t/s)
improper: l = 3.6-1 vt, accompanied by text saying, "where l is in meters, v is in kilometers per hour, and t is in seconds
- The NIST Reference on Constants, Units, and Uncertainty / SI Unit rules and style conventions / Quantity equations

I agree that equations look more complicated than they really are in this form.
WaveWhirler (talk) 22:27, 27 February 2015 (UTC)

## RHP?

In TSS Maianbar, RHP is a piped link pointing here. I assume it's "rated horsepower" but I'm not clear whether that's different from saying it's rated at x horsepower.

In any case the lack of reference to RHP in the horsepower article will be confusing for someone following that link. --Chriswaterguy talk 23:58, 22 April 2015 (UTC)

Rated horsepower (rhp) is the nominal horsepower (nhp) of the engine. TSS Maianbar is updated.
85.110.3.22 (talk) 07:53, 27 April 2015 (UTC)

## 800 watts /hp

I am puzzled why early on in the article, the third sentence states "The most common horsepower—especially for electrical power—is 1 hp = 800 watts." I believe that should read "The most common horsepower—especially for electrical power—is 1 hp = 746 watts." Of the 5 definitions listed in the definition section, none would round to 800. Three of the 5 definitions would round to 746 or 750 or 700, one to 736 or 740 or 700, and none round correctly to 800. Three quarters of a kilowatt is a very useful and pretty accurate approximation, ~0.5% error. I've rarely if ever encountered using 4/5 of a kw (800 watts) as the approximation, in about 4 decades of engineering practice. — Preceding unsigned comment added by 144.92.224.3 (talk) 16:40, 2 July 2015 (UTC)

## rounding correction

Slight correction on rounding; rounding to 735 in one definition, not to 736, since value indicated is ever so slightly below 735.5, the round-to-even does not come into play. — Preceding unsigned comment added by 144.92.224.3 (talk) 16:45, 2 July 2015 (UTC)

## eshp

might somebody please deign to explain what the designation "eshp" - very much in use to quantify the power of aircraft engines - means, contentwise and letter by letter? the article "Kuznetsov NK-12" e.g. links here, but I for one can't find the combination of letters... thanx! --HilmarHansWerner (talk) 05:57, 2 January 2016 (UTC)

## "Break" horsepower

BHP stands for "break horsepower"? What does the "brake" in "brake horsepower" mean? Should be covered in the article IMHO.--Polis Tyrol (talk) 08:24, 5 January 2016 (UTC)

## Indicated horsepower, {{convert}} and unit conversions?

There are a couple of problems with {{convert|5,600|ihp|lk=in}}: 5,600 indicated horsepower (4,200 kW)

Firstly it links to a section within Horsepower; if it used a redirect instead this would be more robust. Secondly it gives a conversion to kW. Is this really credible as a conversion? This isn't a nominal or tax horsepower, where it would be simply wrong, but it is also quite inaccurate, as indicated horsepower ignores a number of major losses that would have to be included for any way to measure kW, such as by brake horsepower.

Should this conversion be supported? Or is indicated horsepower simply a stand-alone measure? Andy Dingley (talk) 23:18, 19 April 2016 (UTC)

The unit is horse power, which has several context-specific forms, e.g. electric/water/boiler horse power as well as several measurement-specific forms, e.g. indicated/nominal/break horse power, all of which express the measured quantity in terms of the very same unit (i.e. horse power) despite consisting of different symbols in the unit's abbreviation, which reflect different contexts and/or different principles of measurement.
The additional factors (e.g. friction, vibration, etc.) that are neglected/accounted-for in the definition of a particular context/measurement-specific form of a unit will most definitely be different for different products, and they may not be the same even for two samples of the same product that came out of the same production line (and will almost definitely vary with time). Therefore a context/measurement-specific form of a unit, in any system of measurement, is _not_ subject to conversion.
My suggestion would be that the default behaviour of the conversion template for context/measurement-specific forms of units should be double-output indicating the essential equivalence to the underlying unit (hp in this case) and the corresponding SI counterpart, e.g. {{convert|5,600|ihp|hp kW|lk=in}}: 5,600 indicated horsepower (5,600 hp; 4,200 kW). Removing the support for the conversion entirely is also an option as you questioned, but then again inclusionism seems to be fashionable in Wikipedia. Frankly, I don't think anybody would look for a generic conversion for a context/measurement-specific form of a unit, therefore its presence would not be a bigger problem than its absence, I think.
WaveWhirler (talk) 20:10, 23 April 2016 (UTC)
I've been accused of being an inclusionist before, but I think we should only include things when their advantages outweigh their disadvantages.
There's no point in a numerically precise conversion from ihp to W as this is just never going to be accurate. An approximate conversion is something a reader already familiar with the meaning of ihp is going to do in their head. Offering a conversion to a naive reader is to mislead them: it implies that 1 ihp = 746W, when it's some sizable factor less than this. Andy Dingley (talk) 22:00, 23 April 2016 (UTC)

## Equals equals equals

What the hell are all the "equals" supposed to mean in the "Measurement" section? — Preceding unsigned comment added by 124.150.172.94 (talk) 13:03, 12 June 2016 (UTC)