On Wed, 01 Oct 2003 10:32:56 -0700, Jim Kelley
wrote:

Gene Nygaard wrote:
They are incorrect in the doctor's office, and even more incorrect in
the supermarket or the jewelry store. Like I said, you don't have to
call the quantities used there "weight"--but if you do call them
weight, use the definition which is correct in that context. Don't
misinterpret what is being used there.

Do you know what you're talking about Gene? Cuz I sure don't.

It's generally accepted that weight is a force.

I've shown in this thread from the experts in the field, including
NIST (the U.S. national standards agency) and ASTM (an industry
standards agency) and NPL (the U.K. national standards agency) and the
Canadian Standard for Metric Practice, that this is false.

I don't agree.

All of
these sources and many others tell you that weight is an ambiguous
word, with several different meanings.

What physical quantity do you think a grocery store scale measures?

You can probably figure that out for yourself, if you stop to think
about how they are tested and certified.

Especially if you have enough common sense to figure out that when we
buy and sell goods by weight, we wouldn't want to measure some
quantity that varies with location.

Another big clue is the units in which that quantity is measured;
grams in most of the world, and at least on prepackaged goods in the
United States. In that regard, you might also consider how the law
defines a pound (i.e., 0.45359237 kg), and then ask youself why in the
world the law bothers defining a pound in the first place.

When I was a kid, almost all the scales in the grocery stores were
balances. You do understand what Richard Clark, among others, has
told us about what we measure with those balances, don't you? Sure,
they had evolved to the point where you didn't have to place loose,
individual weights on a pan to get them to balance. The store we used
most often had one with a dial readout, and a computing scale listing
total price based on various prices per pound, but it prominently
displayed the company motto on the side facing the customer:

HONEST WEIGHT
NO SPRINGS

That scale wouldn't give you any different reading atop Mt. Chimborazo
or at the North Pole than it did in the store in which it was used.
Now, after the invention of the microprocessor, we have other options
with reasonable cost and performance to accomplish the same thing.

Problems can arise when
someone claims a mass is a force and vice versa.

I agree.

And so a torque wrench has what kind of units printed on its scale -
mass and distance, or force and distance?

Once again, it doesn't cost you any more to pay attention.

Like I told you a long time ago, my torque wrench has "meter
kilograms" on it. What does that tell you? Why didn't you answer me
then?
Message-ID:
Date: Fri, 26 Sep 2003 23:35:11 GMT

Though I have had mine for several years, such torque wrenches, of
course, are still readily available.
http://jcwhitney.com/webapp/wcs/stor...&storeId=10101

They are units of force and distance, if you can't figure it out, just
as the "foot pounds" which are the other units on my wrench are. But
just as the existence of the kilogram force does not prove that pounds
are not units of mass, the existence of pounds force does not prove
that pounds are not units of mass.

You could, of course, argue that we should all change to your usage.

Many people already have, obviously.

Not very many, surprisingly.

Just the ones who write physics books maybe?

It is much more common to find people
claiming, erroneously, that there is some error in that usage.

You're the first guy I've ever seen making claims about errors in usage.


Like slugs, poundals only exist in one limited purpose system
of mechanical units, mostly used to simplify calculations.

But you'd like us to believe the unit of mass in that system is
ubiquitous and universal, and that everybody is wrong!

The pound, of course, like the foot and the second, predates that
system, and those units are all used in many other systems as well as
outside any such specialized system. IIRC, there is only at most one
unit in any of the commonly used specialized systems of English
mechanical units that was invented specifically for use in that
system: the poundal in the absolute fps system, the slug in the
gravitational fps system, the slinch in the gravitational
inch-pound-second system. The old metric cgs systems have two
mechanical units with special names that aren't in other systems, the
dyne and the erg, and of course they also have various names in the
different flavors of cgs for electrical and magnetic units, quantities
that have never been measured in English units. Of course, you also
have combinations involving those units, such as foot-poundals.

That the poundal system is much older than the slug system is merely
one of the many clues as to which is older, the pound mass or the
pound force.
Gene Nygaard
http://ourworld.compuserve.com/homepages/Gene_Nygaard/