[time-nuts] FW: Pendulums & Atomic Clocks & Gravity
wbeam at gci.net
Tue May 29 10:08:52 EDT 2007
On Tue, 29 May 2007 22:27:42 +1200, Dr Bruce Griffiths wrote:
>Bill Beam wrote:
>> On Tue, 29 May 2007 16:31:40 +1200, Dr Bruce Griffiths wrote:
>>> Ulrich, Didier
>>> Talking about forces, gravitational fields etc makes no physical sense
>>> if the observer's reference frame isn't specified.
>>> For an observer in/on a satellite orbiting about the Earth with their
>>> reference frame fixed with respect to the satellite.
>>> There is no gravitational field, whatever methods chosen to measure a
>>> gravitational field (within the satellite) will always produce a null
>> Not true.
>> Very simple experiments will show occupants of the satellite that they
>> are in a non-inertial reference frame. (Release a few test masses
>> about the cabin and you will observe that they move/accelerate for no
>> apparent reason, unless the satellite is in free fall which you'll know soon
>> enough,) The experimenter must conclude that the satellite is undergoing
>> acceleration due to the influence of an attractive (gravitational) field.
>> Just because NASA calls it 'microgravity' doesn't make it true. It means
>> NASA is wrong. Weightlessness is not the same as zero-g.
>Only, if you insist on sticking to Newtonian physics with all its
This discussion began as a classical problem. The relativistic effects
are many orders of magnitude smaller than Newtonian (v/c=2.6e-5).
For example: A test mass released on the Earth side of the satellite
cabin will advance in its own orbit a few mm/sec faster than one released
on the far side due to purely classical differences in orbits. Easily observable
without even using a timepiece.
Once your feet leave the ground, not even Newtonian mechanics is
intuitive. Who would have thought that 'putting on the brakes' to
leave orbit would cause a satellite to speed up....
>>> Pendulum clocks fail to work, given an initial push they will just
>>> rotate around the pivot, provided the pivot suitably constrains the
>>> motion of the pendulum (ie a shaft running in a set of ball or roller
>>> bearings or similar and not a knife edge pivot).
Run the numbers - depends on how hard the push.
Consider sheeparding of material in Saturn rings by small moons.
>>> If, however the satellite acts as a rigid body and has a large enough
>>> diameter then it would be possible for an observer on the satellite to
>>> detect a gravitational field gradient.
>> Therefore, you must conclude that somewhere inside the satellite g is not zero.
>A finite gradient doesn't imply that the field itself is nonzero, except
>of course towards the extremeities of the satellite.
Of course it does.
If g=0 everywhere in the neighborhood of a point then the gradient is zero.
Else, what is the meaning of gradient?
Grad not zero implies field not uniform implies not(field zero everywhere).
>> Bill Beam (PhD, physics 1966, past tenured Associate Professor of Physics)
>> Bill Beam
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