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Re: What is weight? (was Re: Internal or external?)



On Sun, 10 Oct 1999, Robert Carlson wrote:

John,

This brings to question the area that most students will be working in. Is
Newtonian mechanics their bread and butter? Are most of your students going
into areas of engineering or pure physics? Is the new definition better for
their understanding in subsequent engineering courses? Or, is this not an
important issue for you and your students? How is the new model an
improvement in these areas when the old model works just fine?

Bob,

As I've mentioned in the past when this subject came up, there is a time
and a place for everything and the intro course is, IMO, a place to stay
pretty squarely in the Newtonian world. Most engineers (who do indeed
comprise the great majority of my students) may never have any genuine
need to go beyond that world, although it saddens me to think of such
talented folks missing out on the awesome beauty of twentieth century
physics.*

On the other hand, one needn't go out of one's way to use language that
will make the ultimate transition from Newtonian gravity to GR a little
easier for those who do go on. The definition of weight is probably one
of the best examples of this.

Students already have experience with the fact that their weight depends
on their motion (whether or not they would describe it that way) and it
isn't that hard for them to understand the concept of "artificial
gravity." These can be drawn on to help motivate the definition of weight
as "what a scale reads" (with the caveat that the scale must exert the
only non-gravitational force).

But my comments in this thread have been directed more to us as teachers.
At the very least, I think *we* ought to have a pretty clear understanding
of what our best theory of gravitation--now nearly a century old--has to
say about the meaning of g.

John

* My father, a *very* talented and now retired electrical engineer, is
currently (at age 73) just learning about quantum mechanics and loving
every minute of it.

John Mallinckrodt mailto:ajm@csupomona.edu
Cal Poly Pomona http://www.csupomona.edu/~ajm