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Re: summary of weight



This is just to clarify that I am not totally sure what camp I am in.
I see merits in several viewpoints.

However, one viewpoint I have, which comes from my chemistry background
is a fondness for the wording "apparent weight." This wording is
extremely common in the chemistry realm, but no one seems to be using
it in the physics realm.

It seems perfectly obvious to me that what your scale reads (assuming
it is a force scale rather than a freshly calibrated mass balance) is
an apparent weight.

The apparent weight includes all the artifacts we might want to
"correct out" if we want to arrive at the true weight. The problem
becomes one of agreeing on which artifacts should be corrected out, and
which are left in, when we attempt to calculate the true weight.

It seems most of us on this list would agree that buoyancy is something
that should be corrected out. That is, buoyancy is one of the things
that makes the apparent weight different from the true weight.

We don't agree on whether a locally accelerating frame (e.g. free fall)
is or is not a correction in going from apparent weight to true weight.

In the chemistry camp I was taught that it is. Explicitly, astronauts
in orbit have an apparent weight of zero, but their true weight is
almost as much as it is it on earth. I guess this is consistent with
camp 1.

What I don't remember well is what the chemists say about earth's
rotation, your elevation, and earth's varying density. I think they
would claim these also should be removed as one goes from the apparent
weight to the true weight. I think that means they would know what
their local value of g is, then they would correct the apparent weight
back to some standard value for g. However, I don't know what value of
"standard g" they would use. Would they use Gm/r^2, or would they use
9.80665?

Hence, as I sit here and think out loud, it is probably correct that I
am most closely aligned with the weight = Gmm/r^2 group, i.e. camp 1.
But I am not sure if I think g is Gm/r^2, or whether g is 9.80665.

But I readily admit that, if I am in this camp, is primarily because
that is my background. That is, I am here for reasons similar to the
fact that I basically have the same religious faith as my parents.
That's simply the way I learned it, and it always made some degree of
sense to me.

Michael D. Edmiston, Ph.D. Phone/voice-mail: 419-358-3270
Professor of Chemistry & Physics FAX: 419-358-3323
Chairman, Science Department E-Mail edmiston@bluffton.edu
Bluffton College
280 West College Avenue
Bluffton, OH 45817