On Thu, 18 Dec 2003 19:41:06 GMT, R wrote:

On Thu, 18 Dec 2003 15:30:26 GMT, Gene Nygaard
wrote:

Bad example. All forces, of whatever kind, are totally irrelevant to
the weight on that driver's license.

This is definately the case with most of the women that I know.


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.

Oh, I don't know. Maybe it's because I live in a country using
english-based units; when someone says they weigh 170 pounds, they
mean weight,

How can that make any difference, when those pounds are legally
defined as 0.45359237 kg, all around the world where pounds were used?
It wouldn't make any difference if the NIST example had used
pounds--the only reason it used kilograms is because SP811 is the
official NIST "Guide for the Use of the International System of Units
(SI)."

What is this country which uses the "licence" spelling and has pounds
on the driver's licence? Does Canada, or some of its provinces, have
pounds on the licence? Anyway, if it matters to you, you shouldn't be
the mystery woman without a name and without an email address, or you
should put that country info into a signature or something.

Sure, there are also pounds force, a recent *******ization, something
never well defined before the 20th century. There are also kilograms
force too--they used to be quite acceptable units. The only
difference is that the metric system is still fully supported and
updated, and those kilograms force are not a part of the modern
version of the metric system, the International System of Units.
Nonetheless, we still see many vestiges of their use--but not in the
use of kilograms for body weight. They are units of mass just as the
pounds are, when used for this purpose in medicine or in sports.


as their weight was determined by a device created to
measure weight, not mass.

Nonsense. Sure, we often accept the measurements of a cheap spring
scale as a substitute for what we want to measure. Those scales
aren't very accurate for the measuring either force or mass--if your
mother's scale shows you to be 5 lb more than your scale home showed
an hour earlier, you don't congratulate yourself on a successful
weight loss program, do you?

But what about when you get serious about your weight, and weigh
yourself on one of those platform type beam balances at the doctor's
office or the gym? Those are mass-measuring devices, as are the ones
which promise

HONEST WEIGHT
NO SPRINGS

But that's moot anyhow; while you are
correct in that we are entangled in a difference in semantics, the
real difference is not the one that you are referring to. Peter, for
example, is referring to weight in the Newtonian sense. In this
context, weight is a force, and acceleration is proof of that force.
Peter is correct within the framework that he's talking about. I am
referring to weight in the Relativistic sense.

No. As I had already pointed out in my earlier reply to Peter,
quoting from Sears and Zemansky, your differences are at a more
fundamental level than differences in how you would define it in
Newtonian physics or using relativity. As S&Z said, "There is no
general agreement among physicists as to the precise definition of
"weight."

The differences they are talking about hinge on things like whether or
not "centrifugal force" is accounted for in your definition of weight.

In this context,
weight is not a force, it is part of the geometry of spacetime.
Philosophically, Relativity probably holds more weight in this
argument. The whole problem with the Newtonian perspective in this
case is "what perspective do you approach this from"; i.e., what
gravitational fields do you reference when calculating "weight". Do
you leave out the sun? Do you leave out the galaxy?

That applies whether you are using Newtonian physics or relativity.

Heck, the galaxy
itself is accelerating. Relativity is not bothered by these
questions. Your own point of view is the only one that matters; if
you are in freefall, if you are moving along the geodisc, you are
"weightless". If you're not, you're not.

Under this definition, the Earth itself has no weight.

-R

Yet Cavendish was successful in "Weighing the Earth" (the title of his
paper, IIRC)--in the same meaning used in commerce and for body
weight, not the different force definitions you and Peter have been
arguing about.

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