Re: What is weight?

[John Denker <jsd@MONMOUTH.COM>]

Hi Folks --

The obvious answer is:
        Weight is the gravitational force on a body.

That's all.  Why make it complicated?


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.


==============


On Mon, 11 Oct 1999, Ludwik Kowalski wrote:

> if the weight is not the same thing as "the force
> of gravity" then what is it?

I'm with you, Ludwik!

> You would probably say "weight is zero in a free-falling elevator".
> Right?

I take this to mean that the elevator defines the frame of reference -- in
which case I agree.  But a lab-frame observer watching the elevator would
not agree.

Whenever we permit consideration of reference frames that are accelerated
relative to one another, then weight is not absolute -- it depends on the
choice of refrence frame.

Consider some astronauts training in NASA's "Vomit Comet" (i.e. a KC-135
flying zero-G parabolic arcs for 25 seconds at a time).  According to
observers in the KC-135, the astronauts are weightless.  In contrast,
according to observers on the ground, the astronauts' weight is nonzero,
and is just sufficient to bend their trajectories into the shape of an
parabola.


______________________________________________________________
copyright (C) 1999 John S. Denker             jsd@monmouth.com