Re: Apparent weight

[Leigh Palmer <palmer@sfu.ca>]

> << It doesn't make the problem solving easier, but David Hestenes's fine
> textbook "New Foundations for Classical Mechanics" does not define
> weight at all. >>
>
> Probably because he didn't have too, as it had been previously defined in pre-
> req courses.  Also, it's not a new word and what are words without
> definitions.  Here are some more sources for definitions of weight:

I guess I didn't make my point. Hestenes doesn't enter the controversy
over which, the "true weight" or the "apparent weight", is what we call
"weight" in common parlance. He does represent "apparent weight" by W,
and he does say W = mg, so it is clear that what he means by apparent
weight is what I defined as weight, the quantity measured by a bathroom
scale in the normal manner. There are still books out there that treat
what Hestenes calls "true weight" as being weight. David is a good
friend of mine. I have no difficulty whatever in detecting his intended
irony in the choice of the term "true weight".

> So, do we throw out weight and call it something else?  Re-define it?  I'll
> continue to use it until someone starts a revolution and calls it something
> else with less than six letters.

No. I think we should keep weight, but we should define it operationally
as I have suggested. If a discussion arises of the sort John Mallinckrodt
initiated, so much the better; students will learn from that. I do not
think the operational definition is difficult, nor will it do violence to
students' preconceptions. It only seems to bother physics teachers who
have been raised in another religion. It is not difficult for students to
grasp the concept.

What's not to like about it? Well, it will change the "correct" answer to
some multiple choice questions, like "How does a person's weight change
when an elevator accelerates him upward?" from "(A) It says the same, but
but *apparent* weight increases" to "(C) It increases as the elevator's
acceleration increases". That's what the scale tells the student; that's
what it tells me, too. I think I can live with that change. Of course I
don't give multiple choice tests in physics courses, so perhaps my ox is
not being gored. After all, what is the answer to the question "How much,
in comparison to his weight on Earth, does a person weigh on the surface
of the Moon?"?

Leigh