Re: What is weight?

[John Mallinckrodt <ajmallinckro@CSUPOMONA.EDU>]

On Mon, 11 Oct 1999, John Denker wrote:

> The obvious answer is:
>         Weight is the gravitational force on a body.
>
> That's all.  Why make it complicated?

As a definition of weight it *may* be "obvious"; it certainly is not
"mandatory"; and I don't believe it is even "optimal."  And who's making
it complicated?  Can you answer the question, "What is the weight of a 100
kg astronaut in a 9,900 kg rocket that is subject only to the 100,000 N
thrust of its engines?"  I can and I think most of us would agree that my
answer is correct.  But you'd need to know where the rocket is.

> At 05:26 AM 10/11/99 -0800, John Mallinckrodt wrote:
> > As I said before, I (and others) would have it be "what a scale reads"
> > or, more accurately, the magnitude of the vector sum of all
> > "nongravitational" forces.
>
> Hmmm, that works only for statics.  If I observe a baseball in flight (and
> there was a lot of that last night) then it has the usual weight but the
> "vector sum of nongravitational forces" is much less.

This simply is not true.  It works in *all* situations including the
baseball (which would simply have a small weight while in flight due to
the effects of air resistance).  I'm willing to concede that my definition
of weight is not particularly *useful* for the baseball in flight, but it
certainly is not "wrong."  Besides, why should we even need to talk about
its "weight"?  Isn't it clearer to use the phrase "gravitational force"?

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