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Re: Weight and Mass and Coordinate Systems



At 02:59 PM 9/24/01 -0400, Larry Cartwright wrote:
Is is correct to say that mass is a property of matter that is the same
in every coordinate system; while weight, a force acting on matter,
depends entirely on the frame of reference and coordinate system
employed?

Short answer: Yes.
Longer answer can be found below.

I am thinking, a 75 Kg shuttle astronaut has a mass of 75 Kg in every
and any reference system?

Yes.

The astronaut is "weightless" in a coordinate
system centered on the spacecraft, but has a weight depending on his
mass and altitude in a coordinate system centered on the Earth?

Yes. And you can leave off the quotes on weightless.

The weight force usually associated with 75 Kg of mass is about 165 lbs at
the Earth's surface, but decreases to about 150 lbs at shuttle
altitude?

Yes.

The weight force even varies depending on whether one's
coordinate system assumes a stationary Earth or a rotating Earth, does
it not?

Yes, although the difference is slight.

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

In modern physics, mass means rest mass. It is relativistically invariant,
that is, manifestly independent of the choice of reference frame.

BTW, even saying "rest mass" is a pleonasm, like saying "apple fruit". The
word "apple" by itself already means the fruit of the apple tree.

There are !rare! exceptions to the rule, so rare as to be not worth
discussing. The exceptions will be obvious from context.