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Re: Apparent weight

What Roger says below is how I try to resolve the problem in my classes; I
don't define weight as the force of gravity on an object, but rather as what
the "bathroom" scale reads. Then there is no problem for astronaughts, they
are weightless and there is a force of gravity acting on them, which
provides the centripetal force that . . .

Joel

PS. the above is obviously the intro physics discussion.
----------
From: Roger Pruitt
To: QuistO; RAUBERJ; phys-l
Subject: Re: Apparent weight
Date: Friday, February 13, 1998 8:03AM

Rick Tarara wrote:

-----Original Message-----
From: Leigh Palmer <palmer@sfu.ca>
Let me try and take up Ludwik's sword here. First of all I don't like to
talk about 'Gravity' without the qualifiers--the Force of, or the
acceleration due to. With the first--the force of gravity is (as we all
know) described at levels below General Relativity as the force of
attraction between masses. The shuttle (and passengers) are being pulled
towards the earth with a gravitational force that is approximately 90% of
that which they would undergo if sitting on the surface of the earth.
Likewise the acceleration that they experience, due to this force, is also
about 90% of the 9.8 m/s^2 they would experience (in free fall) at the
surface of the earth. Since this force is so common (and in fact
dominates
our experiences) we have a special name for it--weight (the attractive
force
of the earth {or other very massive body} on an object). HOWEVER, our
physiological EXPERIENCE of this gravitational force IS NOT the earth
pulling us towards its center, but rather the everyday phenomenon that
something pushes on us in the opposite direction such that we don't
actually
accelerate 'downwards'. Right now, my chair is providing me that
sensation
of weight. When the upwards compensating force is somehow removed, our
experience is one of 'weightlessness' even though in general, such
experiences will accompany a definite acceleration downward DUE to the
force
of gravity. A high dive, bungee jump, the free falling elevator, and the
space shuttle are examples of where the 'upwards' force is absent despite
the fact that the 'downward' force of gravity is still present. It IS
THIS
UPWARDS force that produces what Ludwik and I like to call the APPRARENT
weight. Using this concept one can go on to examine one's experiences on
say a Ferris Wheel and other carnival rides as well as those of free fall
and the space shuttle. Students can handle this approach (without math
mind
you) in almost any level introductory course.

Rick

I see. Gravity is responsible for weight, and in the case of the shuttle,
it is responsible for weightlessness. I'm sorry, Ludwik; that would
utterly
confuse me if I didn't understand the topic thoroughly. Understanding it,
I
reject it. Please give me an operational definition of either "gravity"
or
"gravitational field". Otherwise the question of "What is the gravity in
the space shuttle?" cannot be resolved except by your adjudicating it.

Leigh



How about operationally defining weight as that which is measured when
you step on a scale? Stepping on a scale in the space shuttle would
result in a zero reading. Thus the person is weightless. This also
relates to Rick's comment, "Right now, my chair is providing me that
sensation of weight. When the upwards compensating force is somehow
removed, our experience is one of 'weightlessness'." The force of
gravity is still acting on the astronaut so there should be no problem
when discussing that the astronaut and shuttle are falling around the
earth.

Roger
--

================================
| Roger A. Pruitt, PhD |
| Department of Physics |
| Fort Hays State University |
| Hays, KS 67601 |
| Ph. (785) 628-5357 |
================================
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Subject: Re: Apparent weight
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