Gene Nygaard wrote:
> 
> Curt Fischer <crf3@po.cwru.edu> wrote in message news:<3EE673E0.A6907CF9@po.cwru.edu>...
> > Ken wrote:
> > >
> > > Curt Fischer wrote:
> > > >
> > > > Brett Robson wrote:
> > > >
> > > >>>The last I heard, the Avoirdupois pound was defined as being the weight of
> > > >>>27.7015 cubic inches of distilled water at 62 degrees F with the barometer
> > > >>>being at 30 inches.
> > > >>
> > > >>1. avoirdupois pound is not an imperial pound
> > > >
> > > > You're right here.  Congratulations.  Don't let it go to your head
> > > > though....
> > > >
> > > >>2. your definition is pound-force not pound
> > > >
> > > > A pound force is a pound.  So what are you talking about?
> > >
> > > Well, Kevin's obsolete definition might have been better if he had said
> > > *mass* instead of "*weight* of 27.7015 cubic inches...".
> >
> > But since the pound has historically been a unit of force,
> 
> Wrong. Pounds have always been units of mass.  Pounds force are a
> recent spinoff, something that was never well defined before the 20th
> century, and which even today don't have an official definition.
> 
> Only one of the hundreds of pounds used throughout history has given
> rise to a force unit of the same name--that's how recent the history
> of the pound force is.
> 
> > it is
> > definitely better to speak of "weight".
> 
> That's a big part of your problem, a failure to understand that
> "weight" is an ambiguous word, one with more than one meaning.  It is
> a synonym for mass (in physics jargon) more often than it is a
> particular kind of force in archery jargon for draw weight of a bow,
> or a different kind of force (due to gravity) in physics jargon.
> 
> The troy units are units of weight--but they are always units of mass,
> never units of force.
> 
> Weight means the very same thing as mass (in its physics jargon
> meaning) whenever anyone talks about "net weight" or "troy weight" or
> "carat weight" of a diamond or "dry weight" or "atomic weight" or
> "molecular weight" and in many other instances.
> 
> >
> > > One might speak of weightlessness, e.g. in orbit.  It wouldn't occur to an
> > > astronaut, however, to say that he/she's massless...  Astronauts composed
> > > of non-baryonic matter, and hence travelling at light speed, would be an
> > > interesting concept, indeed...
> > >
> > > For those confused about these notions, the pound-force is the weight, or
> > > *force* exerted by a pound of mass subjected to an acceleration of 1G; as
> > > such, its expression in SI units would be in Newtons.
> > > The pound, OTOH, is a unit of *mass*, and would be expressed in SI units
> > > in Kilograms.
> >
> > According to every technical book I have ever used, the pound is a unit
> > of force.
> 
> Pounds force exist.  Many technical books use them (and so do people
> in their everyday lives, usually as part of a unit of some other
> quantity such as pressure), but many of those which do also use pounds
> as units of mass.  Furthermore, even the ones which don't use them as
> units of mass usually mention pounds as units of mass; it is only in
> the past couple of decades that you can run into a few  textbook
> authors so poorly educated that they don't understand that pounds are
> units of mass.
> 
> >Ergo, pounds measure weight.
> 
> There's no "ergo" about it.  Pounds often measure weight when they are
> units of mass.  Pounds force occasionally measure weight, but are most
> often used for various types of force that are never called weight.
> 
> >Kilograms measure mass.
> 
> True, with two big caveats.
> 
> When they are units of mass, they are units of weight:
> 
> NPL (the U.K. national standards laboratory) FAQ
> http://www.npl.co.uk/force/faqs/forcemassdiffs.html
> 
>     Weight
>     In the trading of goods, weight is taken to mean the
>     same as mass, and is measured in kilograms. Scientifically
>     however, it is normal to state that the weight of a
>     body is the gravitational force acting on it and hence
>     it should be measured in newtons, and this force
>     depends on the local acceleration due to gravity.
>     To add to the confusion, a weight (or weightpiece)
>     is a calibrated mass normally made from a dense
>     metal, and weighing is generally defined as a
>     process for determining the mass of an object.
> 
>     So, unfortunately, weight has three meanings
>     and care should always be taken to appreciate
>     which one is meant in a particular context.
> 
> NIST (the U.S. national standards laboratory) Special Publication 811
> (1995 ed.), Guide for the Use of the International System of Units
> (SI):
> 
> http://physics.nist.gov/Pubs/SP811/sec08.html
> 
>     In commercial and everyday use, and especially in common
>     parlance, weight is usually used as a synonym for mass.
>     Thus the SI unit of the quantity weight used in this
>     sense is the kilogram (kg) and the verb "to weigh" means
>     "to determine the mass of" or "to have a mass of".
> 
>     Examples:  the child's weight is 23 kg
>                the briefcase weighs 6 kg
>                Net wt. 227 g
> 
> Second caveat:  kilograms force also exist, and used to be quite
> acceptable.  They were officially endorsed by the CGPM in 1901 when
> they adopted a "standard acceleration of gravity" for the purpose of
> defining grams force, and were acceptable until the adoption of the
> International System of Units (which doesn't include kilograms force)
> in 1960.
> 
> We still see many vestiges of the use of this once-acceptable unit
> today:  pressure gauges in kg/cmイ, torque wrenches in
> "meter-kilograms" (the SI unit is newton-meters) are still readily
> available, and thrust of rockets or jet engines (as they were most of
> the time in the Russian space program into the late 1980s or early
> 1990s, or in Tom Clancy's nonfiction work _Airborne_, 1997).
> 
> >This
> > is the reason that, in English (Sepponian) units, there is a no
> > non-unity non-dimensionless constant called  gc (g sub c), which relates
> > force to mass.
> 
> So, in this dreamworld of yours, what exactly is the standard for that
> pound?  What is its nature--something electrical, mechanical, or what?
>  Exactly when (to the year is good enough, or a range of years if you
> cannot do any better) was it made a standard, and by whom?  To whom
> does that standard apply?  Who maintains this standard, and where is
> it kept?
> 
> >Here's a quick review for those of you having
> > difficulty:
> >
> > http://gems.mines.edu/~mckinnon/DCGN209/Handouts/gc%20summary.pdf
> >
> > Further evidence that the pound is a unit of force comes from
> > established terms like "ft-lbs", which I hope everyone will agree is a
> > unit of torque, not some mysterious unit of dimension (mass)x(length).
> 
> Yes, it is ftキlbf for energy or work, and either ftキlbf or lbfキft for
> torque.  In earlier times, and in places outside North America,
> foot-poundals were more common for these purposes than they are not.
> 
> American Society for Testing and Materials, Standard for Metric
> Practice, E 380-79, ASTM 1979.
> 
>      3.4.1.4 The use of the same name for units of force
>     and mass causes confusion.  When the non-SI units
>     are used, a distinction should be made between force
>     and mass, for example, lbf to denote force in
>     gravimetric engineering units and lb for mass.
> 
> Of course, symbols for units of measure should also remain unchanged
> in the plural--no language-specific "s" at the end, for example.
> 
> Now, you define for us a British thermal unit.  How much water?
> That's not the water which exerts a certain amount of force, is it?
> 
> What does it mean if a physicist says the latent heat of fusion of
> water is 80 Btu/lb?  Or measures specific heat capacity in
> Btu/(lb薫F)?  What are those units in the denominators?
> 
> >
> > You might also want to check out what a "slug" is.
> 
> Tit for tat.  You ought to check out what a poundal is.
> 
> This is the English unit of force in a system which is much older than
> the one which contains slugs.
> 
> Slugs are a little used 20th century invention, which didn't appear in
> engineering textbooks before 1920 or in physics textbooks before 1940.
>  They exist only in one specific system (out of several such systems)
> of mechanical.  After a brief heyday, mostly in the U.S. and Canada
> (they weren't ever used much in any other places using English units),
> they have pretty much disappeared again.
> 
> The system of mechanical units in which slugs exist is, like SI, a
> "coherent" system of units, as that term is used in metrology jargon.
> That means that in the only system which has slugs, there are no pints
> or gallons of any kind, not U.S. liquid nor U.S. dry nor imperial.
> There are no horsepower, no Btu, not even any psi because there are no
> inches or miles or ounces.  These specialized systems of mechanical
> units are only used only in calculations, and you often have to
> convert into those systems before you can use them, or out of them at
> the end because the units you want to use aren't in that system, or
> both.
> 
> Poundals are the derived units of force in a different coherent
> foot-pound-second system of mechanical units.  They are the force
> which will accelerate the base unit of mass in this system at a rate
> of 1 ft/sイ.
> 
> Fill in the blank:  the base unit of mass in this oldest fps system of
> English mechanical units is the _____________.  (Hint: it is the "p"
> in this fps system.)
> 
> >
> > >
> > > >>3. your definition is /less/ accurate than using a standard object
> > > >>   (perhaps this would be an interesting homework project for you.
> > > >>   Discuss a practical way of maintaining as constant the 3 variables,
> > > >>   volume, temp, and atmospheric pressure. Be sure to mention the
> > > >>   effect of measurement on values)
> > > >
> > > > Umm, why couldn't you use any number of commercially available devices
> > > > to maintain the desired temperature, volume, and pressure?
> > >
> > > First, because mass definitions involving a measurement of pressure
> > > might be circular, as the standard pressure definition relies on mass,
> > > acceleration and surface units... (Hint: how is the Pascal defined?)
> >
> > Yes, but the definition under discussion here was not a definition of
> > mass.  Ergo, no tautology.
> 
> Wrong.  It was a definition of mass--you are just too dumb to
> understand one of the words used in that definition.
> 
> >Your points about accuracy are well-taken; I
> > do understand that there were reasons that the weights and measures
> > people adopted the Pt-Ir standard.  But if 1893 levels of precision are
> > what we're talking about, then the devices today would perform
> > admirably.
> 
> You cannot measure force today to anywhere near the accuracy which the
> weights and measures experts could measure mass in 1893.
> 
> > Oh, I see, wait...Brent may have misinterpreted as serious Kevin's
> > suggestion that we return to English units!
> >
> > > Second, because there's no practical way to measure and regulate the
> > > volume, temperature and pressure with the required precision.
> > > The Pt+Ir mass references have an estimated error in the 10**-9 to
> > > 10**-8 range, which is the major reason these seemingly quaint objects
> > > are still used, well, as mass references...
> >
> > If we updated the definition to be the weight of a certain volume of
> > liquid water at its triple point, wouldn't that take care of the
> > temperature and pressure problem?  How hard is it to measure volume
> > precisely?
> 
> How easy is it to maintain a whole pound of water at exactly that
> triple point, all the way to the edge of the container?
> 
> A lot harder than it is to measure mass precisely.
> >
> > > There's no better mass reference system known as of yet, even though
> > > some new ideas are being investigated -- e.g. the Avogadro crystal
> > > lattice approach based on accurately estimating the number of Si
> > > atoms in a "perfect" sphere, whose dimensions are controlled by
> > > interferometry.
> >
> > What is the current uncertainty in Avogadro's number?  Why can't the
> > standard unit of mass be the nucleus of one atom of carbon-12, which
> > already has an atomic mass of 12 amu by definition.
> 
> Because your eyesight isn't good enough to count the number of those
> atoms I use to balance a kilogram of hamburger--even if you had the
> time and the ability to do the actual counting.

Thanks for your exhaustive response.  It appears that I have been
systematically miseducated by a number of professors and widely used
textbooks throughout my career as a Sepponian engineering student. 
Sorry for anything incorrect I may have said.  

Secondly, Google reveals that you have dedicated a large portion of your
usenet presence to proselytize these facts to the multitudes.  Why such
tenacity?

-- 
Curt Fischer