On Thu, 25 Sep 2003 06:45:29 -0400, wrote:

Gene Nygaard wrote:

Apparently you are claiming that pounds are not units of mass.

Where did you learn that?

Being the skeptic that I am, how can I convince myself that that is
true? Is there some textbook, or something from some national
standards agency, that would help me verify this?

Gene Nygaard

Nice web page you have on the subject, but I suspect it is not
quite so cut and dried as you make out.

It is. I never claimed that pounds force aren't used also.

I have a strong recollection (from many years ago) of being
taught that pounds where force. Going to google with 'pound
mass force' yields some modern university teaching material
which says the same. My ancient thermo text uses lbf and lbm
throughout to eliminate confusion.

But that isn't what our resident Capital-M Metrologist was telling us.
He claimed flatout that pounds are not units of mass.

Furthermore, he also set the ground rules that I could prove him wrong
from the NIST web pages. Yet even though I have indeed done not only
that, and with a dozen other reasons and citations as well, he remains
recalcitrant in his erroneous ways.

Richard Clark is a big windbag, of no substance whatsoever. But much
worse than that is the fact that he has absolutely no integrity.

Yes, some do use lbm and lbf. Or some other variation. I remember
one textbook using p for pounds force and lb for pounds mass.

Here's the way the British physicist who named the slug put in, in the
little treatise in which he introduced this unit to the world:

In the interests of clear teaching, the convention
(which I am glad to see has been adopted in America)
has been adhered to throughout, of using the word
‘pound' when a force is meant, and ‘lb.' when a mass
is meant, and I have ventured to give the name of a
‘slug to the British Engineer's Unit of Mass, i.e. to the
mass in which an acceleration of one foot-per-sec.-
per-sec. is produced by a force of one pound.

It's easy to see why that convention didn't go very far. People would
naturally like to have both a spelled out word and a symbol for both
pounds. He also says, another source showing that Richard Clark is an
incompetent metrologist (and if is also a professional engineer,
guilty of malpractice by his own words because he doesn't follow
NIST's definitions):

British Absolute Unit of Torque. Since in the British
absolute system, in which the lb. is chosen as the unit
of mass, the foot as unit of length, and the second as
unit of time, the unit of force is the poundal, it is
reasonable and is agreed that the British absolute
unit of torque shall be that of a poundal acting at a
distance of 1 foot, or (what is the same thing, as regards
turning) a couple of which the force is one poundal and
the arm one foot. This we shall call a poundal-foot,
thereby distinguishing it from the foot-poundal, which
is the British absolute unit of work.

A.M. Worthington, Dynamics of Rotation: An Elementary Introduction of
Rigid Dynamics, London, New York, Bombay, Calcutta, and Madras:
Longmans, Green, and Co., 1920

As I pointed out to Richard Clark, however, according to the modern
rules, it is the pound force which must be distinguished from pounds
in their original and still most common meaning as units of mass. The
ones using pounds mass (the unit much more often used by those who
care least about the distinction--witness the thousands of items in
every grocery store and hardware store in America measured in pounds)
are the ones who can get away with using the original "lb" symbol.

There seems to be little doubt that today the pound is
defined in terms of the kilogram so is clearly a unit of
mass.

I can't understand how so many science teachers, and even textbook
authors in the past decade or so, can remain oblivious to this simple
fact.

But usage of the pound seems to be less consistent. Consider
pounds per square inch or foot-pounds; in each of these
the pound is a unit of force.

Yes, and for all those items in our stores, the pound is a unit of
mass. For density in pounds per cubic foot or pounds per gallon or
pounds per cubic yard (civil engineers) or pounds per cubic inch
(mechanical engineers), pounds are units of mass. For defining a
British thermal unit, how much water? Certainly not an amount that
exerts a certain amount of force. By the same token, the pounds in
the denominator are units of mass if you say the latent heat of fusion
of water is 80 Btu/lb, or if you express specific heat capacity in
units of Btu/(lb·°F).

Of course, we also have kilograms as units of force when you see the
thrust of jet or rocket engines expressed in kilograms, or pressure
gauges in kg/cm², or torque wrenches in "meter kilograms" rather than
newton meters (still readily available; I have one). The only
difference is that these uses are decreasing. That's because the
metric system is still fully supported and updated, and kilograms
force are not part of its modern version, the International System of
Units (SI). The English units, OTOH, are like obsolete versions of
software--still often usable for the purposes the user wants, but
eventually you may have to upgrade if you want to communicate with the
rest of the world. Nobody is ever going to bother to tell us to stop
using pounds force, without telling us to stop using pounds as units
of mass as well.

I expect the definition of pound will be argued for some
years to come.

Let's just all go metric. The only really confusing measure
there seems to be the definition of the litre.

The litre, of course, is not part of SI. While its definition was
confusing around the time I first learned this, when it was different
from a cubic decimeter, that changed in 1964 when the CGPM redefined
it, restoring the definition as exactly 1 dm^3, and said that under
that definition it would be acceptable for use with SI, something that
hadn't been true for the first four years of the existence of SI.

No. You have the mole, which shares its name with the pound mole and
the kilogram mole, both still used. Guess nobody has the political
will to rename it the loschmitt.

For other non-SI units, of course, the calorie is the absolute worse,
with several different flavors in each of two major groupings,
differing from each other by a factor of a thousand.

Gene Nygaard
http://ourworld.compuserve.com/homepages/Gene_Nygaard/