On Thu, 02 Oct 2003 09:25:38 -0700, Jim Kelley
wrote:



Gene Nygaard wrote:
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.

You misunderstand, Gene. It's not at all clear what _you_ think they
measure. I'm not asking about the units displayed on them. What
physical quantity do you think is actually being measured?

I think that is probably obvious to anybody with half a brain. But it
really doesn't matter, that shouldn't be any impediment to your
telling us where my clues have led you.

Where are you trying to lead me? Maybe you have some strange notion
of what the verb "to measure" means? It wouldn't hurt you to stop and
reflect on that for a moment, and answer it at least to yourself,
before you get to the "Open mouth, insert foot" stage.

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.

They are units of force and distance,

There's the point.

Why are you still refusing to deal with the "meter kilograms" on my
torque wrench, even going so far as to dishonestly snip that out from
the middle of what you quoted, in between your own comments, without
telling us that you were doing so?

Since this involves only force and distance, what could it possibly
tell you about the existence of a unit of mass called a kilogram?
Since this involves only force and distance, what could it possibly
tell you about the existence of a unit of mass called a pound?

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.

Ah, older. So that means.........what?

Let's not overlook the obvious. Perhaps most the most important thing
for your education, and that of several other fools in this thread as
well, that it exists. That's something you weren't willing to admit
in the beginning. But if it didn't exist, we certainly wouldn't be
able to say that it is older. (A corollary, of course, is that if
pound force didn't exist, there would be nothing for these units to be
older than.)

Thus, what you quoted from the appendix of Halliday and Resnick (1981)
was incorrect. Do you agree?

That it is legitimate. Conversely, that it is the pound force that is
the ******* child.

This is also one important factor in the usage rules as spelled out by
the ASTM and followed by NIST, the U.S. national standards laboratory,
and the National Physical Laboratory, the U.K. national standards
laboratory. That is indeed one reason why this unit gets to use the
unadorned name "pound" and the original symbol "lb," while the newer
spinoff needs to be identified as a "pound force" and use the symbol
"lbf" to distinguish itself.

That the troy pounds, in terms of which the avoirdupois pound was
defined for centuries, are units of mass. This doesn't tell you that
they have never spawned units of force of the same name; you have to
figure that fact out by other means.
Gene Nygaard
http://ourworld.compuserve.com/homepages/Gene_Nygaard/