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-----Original Message-----
From: Leigh Palmer <palmer@sfu.ca>
To: phys-l@atlantis.uwf.edu <phys-l@atlantis.uwf.edu>
Date: Saturday, May 02, 1998 12:59 AM
Subject: Re: Centrifugal force
As an afterthought, would it make any difference in the outcome of
Chuck's proposed experiment if the unpowered rocket were resting on the
launch pad (a launch pad one meter higher to be exact) instead of
hovering? A lot of fuel could be saved that way. I would not expect it
to make any difference whether the rocket was supported by the contact
force of the launch pad or the thrust of the rocket engine.
No, it wouldn't. That is the point of Donald's example. Let's stick
to the hypotheses what brung us, eh? Discussion is simpler that way.
If it makes no difference, and we don't have to pay for hypothetical
fuel, please let it be!
Leigh
Yes it would! The rocket must produce an acceleration equivalent to the
(now removed) gravitational field of the earth!
Previously I believed we were on the same page as far as the physics
was concerned, that we only differed in outlook. Now it is clear we
are not in agreement on the physics. I claim the results of the
experiments performed in the rocket depend not at all on whether the
rocket is tethered firmly to the pad and running, running and
hovering above the pad, or resting on the pad. Of course the rocket
must be running after the Earth is removed; we understand that.
By the way, I see what the problem may have been. What was "Chuck's
proposed experiment"? I was under the impression this was Donald's
gedanken experiment under discussion here.
Leigh
Next question. Let's ignore the 'slight bump' but keep in mind that the
rocket DOES have a finite size. If our experiments are accurate enough can
we not measure that two falling objects in the rocket will move closer to
each other because of the non-uniformity of a 'real' gravitational field,
than they would when the acceleration is 'caused' by the rocket blast?
I'm familiar with the word 'local' used to describe the principle of
equivalence and GR, but is there a fundemental arguement that forbids our
experimentally distinguishing between the divergent gravitational field and
the uniform acceleration of the rocket??