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Re: Apparent weight




-----Original Message-----
From: Leigh Palmer <palmer@sfu.ca>


Rick, You're not addressing my question. How can I tell that there
is a gravtational force acting in my frame of reference? What are
the consequences of such a force present? If the force can only be
calculated, what is the difference between it and, say, my shoe
size squared?

Leigh


As Ludwik points out in a later message, the crux of our disagreements rests
on the sophistication of the student and hence the point of view taken for
explaining the 'weightless' condition in the shuttle. You and your students
seem comfortable with dealing directly with an accelerating frame of
reference and the equivalence principle. I've chosen to analyze the
situation from the earth's frame of reference and since from such we
recognize that the shuttle is in free fall, immersed in the earth's
gravitational field, we need a way to explain the sensations experienced by
the astronauts. The apparent weight discription WITH a strong emphasis on
the fact that we tend to experience forces backwards (weight is one, being
pushed 'back' into our seat as the airplane takes off is another) explains
why free fall simulates a weightless condition but IS different (externally)
from being at rest in the shuttle far away from any large gravitational
bodies. This appoach also works well in explaining the 'artificial' gravity
one experiences in a rotating frame (like the space station in 2001) or in
the 'infamous' elevator accelerating 'upwards' (but in deep space) where
one can have a full sensation of weight (including the measurement on
Ludwik's bathroom scale) without a mass generated gravitational field.

This is a topic that I feel is NOT a misconception in the text books. There
are different ways to approach the phenomena some more appropriate to
introductory non-majors courses and others more appropriate to graduate
level General Relativity courses.

Rick