[time-nuts] FW: Pendulums & Atomic Clocks & Gravity

Dr Bruce Griffiths bruce.griffiths at xtra.co.nz
Tue May 29 20:10:02 EDT 2007


Bill Beam wrote:
>>> 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 
>> attendant problems.
>>     
>
> 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....
>
>   
The existence of "privileged" frames of reference in Newtonian mechanics 
and special relativity has always seemed problematic, especially when it 
may be observationally difficult to identify such a frame of reference. 
Fortunately the inertial reference frames are not imbued with the same 
privileges by general relativity.
>>>> 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.
>   
>   
Surely the forces involved are impractically low for a real pendulum.
>> 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).
>
>   
I should have been more explicit I meant a finite gradient at a point 
does not imply the field is no zero at that point.Bill Beam

Bruce





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