# Talk:Foot–pound–second system

## error prone

Describing a system as error prone is WP:SYNTHESIS unless directly supported by a reference. Please include page number to support this content. Note that "incoherent" simply refers

"The FPS system was never made fully coherent by the incorporation of electrical or molar units." (p 52)

.

Gerardw (talk) 10:59, 5 October 2011 (UTC)

Dimensional analysis depends on the variance against the free variables of a theory, not the underlying quantities they represent. Thus in LMT theory, length, mass and time are not defined in the theory, but force is.
Coherence has nothing to do with completeness (ie having electrical units etc).
It has to deal with a 1:1 relationship to a set of formulae. One has for example equations for 'cgs' and 'SI' electromagnetics, each is coherent to its own body of formulae. The ft.lbf/s is a coherent unit of power in the fps system. The horsepower is not, since one has to get a factor of 550 into the system. There is a perfectly legitimate four-dimensional LMFT theory, to which all gravitational systems are coherent. The coherent unit of mass (FT²/L) has names in the fps (slug), inch-pound-second (slinch), cgs (glug), mks (hyl, par, mug or TME). The horsepower, as 550 ft lb/s, converts to a similar sized unit 75 kg.m/s, neither are coherent to the theory.
In any case, it is wrong to suggest that molar or electrical units were not part of the fps system. The candle, for example first appeared in the fps, and was adopted into metric some 20 years later.
The mole-unit was always derived from Mass, (even to things like (kgf.s²/m)-mol in some ICAO atmosphere). The unit was alway M=M/u. SI does not use the coherent kmol unit, but opts to use the gram-mol, which leads to a new dimension N = M/ku.
Electrical and magnetic units were by gaussian/esu/emu systems, which requires only LMT to be defined. One can tell from the dimensions and the quantity whether the esu or emu are implied, the conversion factor is c.

Wendy.krieger (talk) 11:52, 6 October 2011 (UTC)

As quoted in an earlier edit summary, the source cited right there says in section 1.2.5: “This is an essentially incoherent system and requires great care in its use.” Saying it’s “error prone” is just paraphrasing that. — Christoph Päper 13:29, 29 October 2011 (UTC)
It's hardly a 'paraphrase'. The two mean entirely different things.
“that” was meant to referr to “requires great care in its use”, not to “essentially incoherent”. — Christoph Päper 08:57, 31 October 2011 (UTC)
Coherence is a relation between a measurement system and its formulae. There are coherent imperial units used in each measure, but the formulae were different to those used in SI.
As i noted earlier, the molar units were always derived, until the people who use SI decided to opt out of the coherent unit (kmol), and use an incoherent unit needing a new base unit. The coherent unit is simply M/u, where u is the dalton as a natural constant. All systems have coherent electrical units by way of the gaussian theory. In either case, it's exactly like saying that the SI is incoherent because it has no money unit, even though both the IWMA of 1924, 1878, and the original metric system, specifies a derived money unit. The US Mint act of 1801 defines currency as well.
great care in it's use is someone's opinion. The fps was the system used by the US and UK through much of the industrial age, when Britain built an empire that covered a third of the earth. So i struggle with this opinion, save to show the author's opinion. In any case, all systems require great care in their use, because one must first judge the coherence of supplied measures. A measure like pound per square inch is simply a pressure unit. It is coherent when force is in pounds, and area is in square inch. Were one to use a pressure in psi in some system where it were not coherent, then a conversion factor is needed. Ditto km/h, knots, km, hour, minute, day, year, ...
"is error-proned" is clearly unjustified. It is no more error-proned than say, metric. In practice, the metrics are more error-proned, because it's easier to slip a decimal in that system. Wendy.krieger (talk) 08:20, 30 October 2011 (UTC)
User:Gerardw asked on my Talk page to discuss my revert of his removal here. That only concerned coherence (and consequently ease of use) of a particular FPS subsystem. I hope we agree that using pound-force and pound-mass together makes an incoherent system. — Christoph Päper 08:57, 31 October 2011 (UTC)
It's only incoherent when the formulae does not support it. Context decides many things. I'm currently reading a book that assumes c=1, and that it's ok to drop 'c' freely. The same logic that restores 'c' will restore 'g' if you need it to.Wendy.krieger (talk) 07:50, 1 November 2011 (UTC)

## The Mole

The unit mole is short for gram molecule, in general, placing -mole, -ion, or -equiv, have the effect of stating N things, N electron-charges, or N valences (where N = avagadro's number = mass-unit / dalton). "Mole" itself is short for "gram-mole". The unit is thus a derived measure from mass, (ie number by weight), with a dimension M. There are indeed references to -mol as an addon to convert (mass) into (moles), eg lb-mol, (kgf-s²/m)-mol [used in the US standard atmosphere], and g-mole, kg-mole.

The SI system does not use the coherent unit (ie mass-unit / dalton), but either uses (gram/dalton) = gram-mole, or kg/kilo-dalton. Since there is plenty of reference to gram-mole, and few to kilo-dalton, one concludes that SI simply adopted established practice and uses the mole.

Since the former relation of (mole-unit) = (mass-unit)/dalton no longer applies, it needs then to be established that the (mole-unit) is no longer a derived measure but one that is independent of the weight. The sentence i wrote is indeed perfectly correct: moles were used with many systems but not as a base dimension, but it needs to be one in SI, because SI is not coherent there. --Wendy.krieger (talk) 07:21, 3 January 2012 (UTC)

## History

It would be nice to have something about when FPS was invented, and when it came into general use. Zyxwv99 (talk) 23:28, 18 January 2013 (UTC)

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