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On 01/02/2013 04:23 PM, Ludwik Kowalski wrote:
What might be measured in a falling elevator is called apparent acceleration.
I don't like terms such as "apparent" acceleration or "apparent"
weight. The weight measured in one frame is no more (or less)
apparent than the weight measured some other frame.
The point is, no matter what you do, it's frame-dependent.
It is the g calculated from the universal gravitational force, either in Spain or in N.Z.
Calculating g is not so simple. In particular, suppose we have
a frame comoving with a freely-falling elevator in Spain. The
elevator is small, but we can extend the /frame/ as far as we
wish. If we extend it all the way to New Zealand, we find that
the framative g is
|g| = 0 in Spain [1]
and
|g| = 2 G M / r^2 in NZ (approximately) [2]
relative to this frame ... with a very remarkable factor of
two in equation [2].
The law of universal gravitation tells us the difference
between these two g-values, but it can't tell us either
of them separately. Einstein's principle of equivalence
guarantees that it can't.
============
Also, to save people the trouble of looking it up, I
should have mentioned that Spain and NZ are antipodes.
If you want another example, Hawaii and Botswana are
antipodes.
Examples are relatively hard to come by. Only about 4%
of the earth's land is antipodal to land.
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