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[Phys-l] Zero-gravity vs. weightlessness



Hi,

I happened to read AAPT periodical "Interactions" (April 2008). There was an open forum letter stating that weightlessness should not be confused with zero- or microgravity. The letter made a distinction between the airplane flying a parabolic path (zero-gravity flight) and the space station following a circular orbit around the earth.

It was explained how in the space station "centrifugal force, due to inertia, equal and opposite gravity makes people and things orbit weightless". On the hand, the aeroplane is flying a parabolic path "that does not resist the force of gravity on the passenger and they are weightless but accelerating toward the earth due to gravity".

I have thought that both cases are equivalent from the point of view of relativity theory: the vehicles execute essentially free motion in gravitational field. Hence, the gravitational field in the frame of the vehicles is very nearly zero in both cases.

Or am I missing something here?

Regards,

Antti

P.S: I know that the term "weightlessness" is quite ambigious but I don't think that it is a problem in these examples.

Antti Savinainen, Ph.D., B.Ed.
Senior Lecturer in Physics and Mathematics
Kuopio Lyseo High School
Finland
E-mail: <antti.savinainen@kuopio.fi>
Website: <http://kotisivu.dnainternet.net/savant/>


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