Post by Richard ClarkPost by Gene NygaardPost by Richard ClarkA balance, by implicit definition again, consists of comparing two
masses under the influence of Gravity. Given it is a bridge, in a
sense, the constant of Gravity is discarded from both sides and mass
is compared only. It is a convenience of earthly expectations (and a
defunct system of measurement) that the scale is marked in pounds.
The matter of convenience is in the other direction, stupid; we're
willing to substitute cheapness for accuracy in what we want to
measure on those unreliable bathroom scales. They aren't any more
accurate for measuring force than they are for measuring mass on
Earth; haven't you ever weighed yourself on your mother's scale or
somewhere else and found it differed from yours at home by several
pounds? Do you automatically assume you've gained or lost that much
weight.
I've nowhere introduced the topic of accuracy. It has nothing to do
with your original query. Weight and mass can both be measured to
considerable accuracy. It all depends on method and standards.
And mass can be measured with much more accuracy than force can, but
that is entirely irrelevant to the point I was making.
Your claim was that the mass-measuring balances are, for a matter of
convenience, marked in units of force called pounds. I say that it is
in fact the other way around, that the cheap force-measuring spring
scales are marked in units of mass, which is indeed what we want to
measure. The kilograms used throughout the world, including most
hospitals in the U.S., for human body weight are indeed the proper SI
units for this quantity. The pounds used for this purpose are the
ones legally defined as 0.45359237 kg. Except, of course, for some
science teachers and some physics books written recently by authors so
miseducated (not uneducated, but actually mistaught) that they believe
pounds are not units of mass.
American Society for Testing and Materials, Standard for Metric
Practice, E 380-79, ASTM 1979.
3.4.1.2 Considerable confusion exists in the use
of the term weight as a quantity to mean either
force or mass. In commercial and everyday use,
the term weight nearly always means mass; thus,
when one speaks of a person's weight, the
quantity referred to is mass. . . .
Because of the dual use of the term weight as a
quantity, this term should be avoided in technical
practice except under circumstances in which its
meaning is completely clear. When the term is
used, it is important to know whether mass or
force is intended and to use SI units properly as
described in 3.4.1.1, by using kilograms for mass
or newtons for force.
This ASTM E 380 and a separate ANSI/IEEE Standard have now been
combined into a joint standard SI 10. I don't know if it says exactly
the same thing; but I am certain it doesn't say anything directly
contrary to this.
Of course, NIST also tells us the same thing. I'll get to that below.
Post by Richard ClarkA bathroom scale is not a balance. A balance has a scale (the marks
along which the balance weights are moved and the markings upon those
same weights).
Post by Gene NygaardPost by Richard ClarkPost by Gene NygaardPost by Richard ClarkHowever, you do ask for a reference and acknowledge the NIST as a
http://physics.nist.gov/PhysRefData/contents-constants.html
There is absolutely nothing about pounds on this page. So don't be
bullshitting us.
That is the whole point. You don't see pounds there for mass do you?
I don't see pounds as units of mass because this page just lists units
in the International System of Units.
Exactly.
So why were you offering it as evidence that pounds are not units of
mass? Do you think I'm that stupid, that you can pull the wool over
my eyes so easily? Guess again.
Post by Richard ClarkPost by Gene NygaardShow me something from NIST saying that pounds are not units of mass.
Or from some textbook.
Post by Richard ClarkThat's because pounds are not a unit of mass. They are a unit of
weight which is NOT a constant throughout the universe (nor on earth
for that matter).
Just your say-so? That's the best you can do?
I am a trained Metrologist. I have measured mass traceable to the
NIST. I have done this in four different Primary and Secondary
Standards Labs. I was the head Metrologist of two of them.
Wow! This is even better than I dreamed of. A genuine Capital-Letter
Metrologist. Of course, it's also pretty sad, as most people will
understand if they stick with me for the rest of this message.
I'm sure that as a Metrologist, you are well aware of one particular
subset of English units, used only in calculations, which is a
coherent, gravitational foot-pound-second system in which the derived
unit of mass is a slug, equal to 1 lbf·s²/ft. One of several such
subsystems, of course.
But if you are really a capital-letter Metrologist, and an old fart on
top of it (that system with the slugs was never used in physics
textbooks before 1940, and even a couple of decades later I learned
the system I'm about to describe first, before learning the one with
slugs--and you must be at least close to my age, and a genuine expert
on weights and measures on top of it all), you'll have a damn hard
time convincing me, or anyone else, that you are also not aware of a
much older coherent foot-pound-second system of mechanical units, the
absolute fps system in which the derived unit of force is the poundal,
the force which will accelerate the base unit of mass in this system
at a rate of one foot per second squared.
Now, fill in the blank, please: The BASE UNIT OF MASS in this oldest
English system of mechanical units is the _______________. Hint: it
is the "p" in this fps system.
BTW, while the gravitational fps system of units enjoyed a brief
heyday in science in North America, outside of North America the
absolute fps system with poundals remained the system of choice for
doing calculations in English units.
You probably also know that both of these limited use, coherent
systems of units are, like SI, coherent systems of units. That means
that in neither of these do we have any pints or gallons of any sort,
not U.S. liquid, not U.S. dry, and not imperial. Nor are there any
Btu, nor horsepower, in either system. Not only that, but there are
no ounces (neither avoirdupois nor troy, nor U.S. nor imperial fluid
ounces), no tons (neither long nor short, neither force nor mass), and
no miles or inches (and thus no pounds force per square inch either).
Of course none of our ordinary measurements are made in the context of
any of these specialized systems of mechanical units which serve as
calculation aids. The fact that many of the we use are not part of
these systems is one bit of evidence of that fact. That fact that
nobody ever measures (as opposed to calculating from other
measurements) mass in slugs is another. The fact that we can
generally choose any of several different systems of units to use in
our calculations, with no change in difficulty, is still another piece
in the puzzle.
Let's look at what the English physicists William Thomson (for whom
the SI unit of temperature is named) and Peter Guthrie Tate had to say
about this way back in 1879, Treatise on natural philosophy, 1879,
reprinted as Principles of mechanics and dynamics, quoted by Jim Carr
in Apr 1998 on newsgroups alt.sci.physics, sci.engr, sci.physics.
"By taking the gravity of a constant mass for the unit
of force it makes the unit of force greater in high than
in low latitudes. In reality, standards of weight are
masses, not forces. They are employed primarily in
commerce for the purpose of measuring out a definite
quantity of matter; not an amount of matter which
shall be attracted to the earth with a given force."
<... description of merchant using spring scale to
defraud or be defrauded depending on latitude,
etc ... Jim Carr>
"It is therefore very much simpler and better to take
the imperial pound ... as the unit of mass, and to
derive from it, according to Newton's definition
above, the unit of force."
Then you might also know what "weights" means in the English versions
of the international bodies charged with keeping our international
standards:
CGPM General Conference on Weights and Measures
CIPM International Committee for Weights and Measures
BIPM International Bureau of Weights and Measures
In the introduction to their SI brochure (available at
http://www.bipm.fr), the BIPM tells us for the first half-century of
their existence, their only responsibility was keeping the standards
for length and for mass. Take a wild guess which of those two
corresponds to "weights" in these names.
Post by Richard ClarkPost by Gene NygaardI can, OTOH, prove that pounds are indeed units of mass.
By a reference found at the NIST? I think you would have done that by
now if you could.
Cocky little bastard, aren't you!
Just making clear that you accept the fact that doing so would prove
you wrong, before I do it.
I have already done so, of course, without referring to NIST, with
that description of the absolute fps system above.
But before we get to wandering around NIST's website, let's do a
little primary source research, and find the definition which NIST
considers controlling. For that we need to look to NIST's
predecessor, the National Bureau of Standards, and to the law of the
land.
Earlier in the 20th century, Congress had had the sense to delegate
the authority to make these definitions to the experts in the field
who know what they are doing, and had given the predecessor of NBS
this authority. This was officially implemented in 1959 by official
regulatory action by NBS, made official with its publication in the
Federal Register of 1 July 1959.
This redefinition of the pound was done in accordance with an
agreement reached among the national standards laboratories of several
of the most advanced nations in the world, not back in the Dark Ages
but in the middle of the 20th century, two years after Sputnik and the
year before the International System of Units was introduced. The old
U.S. definition, which had been a slightly different exact fraction of
a kilogram for the 66 years before then, was replaced by the new
international definition as 1 lb = 0.45359237 kg.
You can read the current U.S. law (this Federal Register Notice), as
well as a discussion of the earlier U.S. law and of the international
agreement, at one of these web sites (same document both places):
http://www.ngs.noaa.gov/PUBS_LIB/FedRegister/FRdoc59-5442.pdf
http://gssp.wva.net/html.common/refine.pdf
Of course, the same definition is was also adopted in Canada, in the
U.K., in South Africa, in Australia, and in New Zealand, the other
parties to this international agreement. It is also used all around
the world, and was adopted by statute or regulation in some other
countries not a party to the original agreement, such as Ireland.
Now, let's get to the NIST web site. You obviously didn't follow the
links you provided to get to the right place. Start with the one you
recommended
http://physics.nist.gov/cuu/Units/units.html
click on Return to Units Home Page which takes you back up one level
to
http://physics.nist.gov/cuu/Units/index.html
click on Bibliography: Online publications and citations to go to
http://physics.nist.gov/cuu/Units/bibliography.html
Go down to NIST Special Publication 811 and first of all, order
yourself a free printed copy of this document. You need it. Then
look at it in the online version, either in .html or in .pdf,
whichever you prefer. I'll use the html version to give some links to
specific parts of it below; I also have the printed version, and I
have the .pdf version right on my computer.
I already know what you think of NIST. In another message, you told
us that "NIST describes all this at the links offered
and they do not equivocate nor banter terms casually. For any
Professional Engineer, they carry the force of law as the only
authoritative source for definition. "
This is NIST's official _Guide for the Use of the International System
of Units (SI)_, by Dr. Barry N. Taylor, reviewed and approved by both
the director of NIST and by his boss, the Secretary of Commerce. It
is cited as an authority not only by many of the national standards
agencies around the world, but also by the BIPM itself.
First, a word about Dr. Barry N. Taylor. He is not only a
professional metrologist with a Ph.D. in physics, but he has also
served on both the Consultative Committe on Units which advises the
CGPM (still on that, I think), and on the SUNAMCO Commission
(Commission on Symbols, Units, Nomenclature, Atomic Masses and
Fundamental Constants) of the International Union of Pure and Applied
Physics (IUPAP).
In other words, for the benefit of anyone else reading this, if
Richard Clark is a "Metrologist" then Dr. Barry Taylor must be a
"METROLOGIST" because even capitalizing all the letters won't
adequately show the difference between the two, especially when it
comes to expertise in the particular subfield related to teh
definitions of units of measure.
First, before we get to the pounds, let's digress a little bit and
finish up that loose end I left above.
http://physics.nist.gov/Pubs/SP811/sec08.html
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 same is true for pounds, of course. Units of mass in this
context, as the term is used in physiology and medicine, and in
sports--the reasons we normally weigh ourselves.
There's more to the explanation in section 8.3, including a good
discussion of the force definition of weight often used in physics and
engineering. This section concludes with the excellent advice that
whenever the word 'weight' is used, it should be
made clear which meaning is intended.
Now, let's go to the extensive list of conversion factors found in
Appendix B to SP 811.
http://physics.nist.gov/Pubs/SP811/appenB8.html#P
To convert from to Multiply by
pound (avoirdupois) (lb) 23 kilogram (kg) 4.535 924 E-01
pound (troy or apothecary) (lb) kilogram (kg) 3.732 417 E-01
[The 23 is a reference to a footnote in the printed and pdf versions,
a note on a separate page in html]
http://physics.nist.gov/Pubs/SP811/footnotes.html#f23
23 The exact conversion factor is 4.535 923 7 E-01. All units
in Sec. B.8 and Sec. B.9 that contain the pound refer to
the avoirdupois pound.
This unit, of course, is not defined by this publication. This is
just the legal definition made by NBS in 1959.
Also, take a look at another section of 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.
As you can see above, this sensible rule is also followed by NIST. It
is also followed by NPL, the U.K. national standards laboratory. It
is the older unit, the one more often used, and the one more likely to
be used by those who care least about the distinction, which gets to
use the original, unadorned symbol "lb"; it is the recent
bastardization, the less often used unit, and the one more likely to
be used by those who care most about the distinction, that must be
distinguished by using a different symbol, "lbf" instead.
Post by Richard ClarkPost by Gene NygaardThat will prove that you are flat-out wrong in your claim that they
are not.
Well, I have seen a lot of math tossed over the transom here. But if
we are to work by your own standard, cite an NIST reference.
Post by Gene NygaardJust for practice, consider the troy system of weights. Unlike their
avoirdupois cousins, and unlike grams and kilograms, the troy units of
weight have never spawned units of force of the same name. They are
always units of mass; a troy ounce is exactly 31.1034768 grams, by
definition. There is not and never has been any troy pound force or
troy ounce force.
Hi Gene,
Sounds like you proved a pound is not mass.
No. You just proved that you are hopelessly ignorant when you get
outside your fields and start discussing things such as linguistics,
history, or the law.
Post by Richard Clark"The 3d CGPM (1901), in a declaration intended to end the
ambiguity in popular usage concerning the word "weight," confirmed
The kilogram is the unit of mass..."
One of the most confusing and impossible to understand resolutions any
political body has ever passed. You will note that NIST places no
emphasis on this whatsoever.
Yes, even then there were evidently enough scientists so utterly
confused as to think that the standards they were keeping were
standards of force rather than the standards of mass which they always
had been. As were the old standards for pounds, naturally. Of
course, by that time, we in the United States has already abandoned
our independent standards for pounds, and we already defined them as
an exact fraction of a kilogram. So where does that lead you?
But of course, you are making a big mistake you think that this
particular resolution meant that we couldn't use kilograms force. In
fact, it was just the opposite--this very same resolution endorsed the
use of grams force and kilograms force by adopting a standard
acceleration of gravity, which is not a concept of physics but rather
of metrology, something which serves no purpose other than defining
units of force in terms of units of mass. Kilograms force had never
been well-defined units before then. Neither had pounds force, of
course--and what's more, even today pounds force don't have an
official definition. The de facto standard, never officially adopted
by any national or international standards agency, nor by any
professional organization, is probably to use the same standard
acceleration of gravity which is official for defining grams force and
pounds force, namely 980.665 cm/s² in the units used in that 1901
resolution, before mks systems had come into use, at a time when
neither slugs nor newtons had ever been used for the units they are
now.
Now go back to that Bibliography page on NIST and download NIST
Special Publication 330, which includes the unofficial English version
of this resolution, or at least the salient parts of it.
http://physics.nist.gov/cuu/Units/bibliography.html
Then pay special attention to the footnote added by NIST, found on
page 17 in the document's own pagination (I don't know the page number
in the pdf format):
[dagger] USA Editor's note: In the USA, ambiguity exists in
the use of the term weight as a quantity to mean either
force or mass. In science and technology this declaration
[CGPM (1901)] is usually followed, with the newton the
SI unit of force and thus weight. In commercial and
everyday use, weight is often used in the sense of mass
for which the SI unit is the kilogram.
Post by Richard ClarkAny other usage of "weight" in regard to the sensation of the action
of Gravity upon an amount of mass is outdated by more than a century
of understanding and convention.
You said weight is a force. This resolution clearly said that weight
is not a force, but merely something "in the nature of a force,"
whatever the hell that is supposed to mean.
But fortunately, in any case, nobody was ever damn fool enough to give
the 1901 CGPM any say-so on what "weight" means for the "net weight"
of my bag of sugar, or for the troy weight of a bar of gold or
platinum. That's outside their authority.
That resolution isn't seriously offered as proof of any change in
meaning of the word. In fact, I doubt that the 1901 CGPM ever
intended to change the meaning of the word--they wrongly thought that
they were merely stating existing definitions.
"Outdated by more than a century of understanding and convention"?
Nonsense. Go back and read that section 8.3 of NIST Special
Publication 811 again. That's 1995--hardly a century ago.
Need more. Here's 1989, in the still-effective official National
Standard of Canada, CAN/CSA-Z234.1-89 Canadian Metric
Practice Guide:
5.7.3 Considerable confusion exists in the use of
the term "weight." In commercial and everyday use,
the term "weight" nearly always means mass. In
science and technology, "weight" has primarily
meant a force due to gravity. In scientific and
technical work, the term "weight" should be
replaced by the term "mass" or "force," depending
on the application.
5.7.4 The use of the verb "to weigh" meaning "to
determine the mass of," e.g., "I weighed this
object and determined its mass to be 5 kg,"
is correct.
Note that "nearly always" is much stronger than "primarily"; they even
got that part right. Note further the difference usage for the noun
forms in 5.7.3 and the verb forms in 5.7.4; for the former, the
meaning is context-specific, but for the latter that definition is
unqualifiedly called "correct" (which does not, of course, say
anything one way or the other about the use of the verb to mean to
determine the force due to gravity, which is also correct).
Need more. Here's 2003, on the web pages on the National Physical
Laboratory (NPL), the official national standards agency of the United
Kingdom of Great Britain and Northern Ireland:
NPL 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.
Note that they are talking about DIFFERENT MEANINGS of the word
"weight." Just as NIST does. Just as ASTM does. Just as the
Canadian Standard for Metric Practice does. Just as any good
dictionary does.
That, of course, is how the word weight entered the English language
over 1000 years ago, meaning the quantity measured with a balance. A
quantity which you yourself explained so lucidly to be mass, not the
force due to gravity. Of course, when those tribesmen in what is now
England were looking for a word to use to measure how much stuff they
have, when they buy and sell goods, they didn't make any mistake when
they invented this word "weight" for that purpose, did they? They
couldn't have used "mass" for this quantity instead, unless they had
happened to choose those phonemes for the word they invented. Mass
didn't have this meaning until more than 750 years later, when some
obscure translator translated Newton's major work into English after
Newton's death. Or do you think it was a mistake that these heathens
didn't figure out the God-given word they were supposed to invent for
this purpose?
There is no error when we use the very same word, with the very same
meaning, for the very same purposes today. We have a prior claim to
this word by 3/4 of a millennium over the physicists who recently
borrowed it and often use it with a somewhat different meaning.
Sometimes we borrow the physicists meaning, sometimes we use the
original meaning. But like all the experts tell you, because of these
ambiguities, you should just avoid using the term "weight" in a
technical context--and if you do use it, make damn sure your meaning
is clear.
Gene Nygaard
http://ourworld.compuserve.com/homepages/Gene_Nygaard/
Gentlemen of the jury, Chicolini here may look like an idiot,
and sound like an idiot, but don't let that fool you: He
really is an idiot.
Groucho Marx