[time-nuts] nubie querie

Bruce Griffiths bruce.griffiths at xtra.co.nz
Fri Mar 5 21:50:35 UTC 2010


Matthew Smith wrote:
> Quoth Bruce Griffiths at 2010-03-06 07:58...
>    
>> Yes it does due to the variation of gravitational attraction between the
>> object and the Earth with height above the ground.
>> However this classical effect is very small and probably virtually
>> impossible to measure.
>>      
> So, if the mass is closer to the centre of the planet, it weighs more?
> Never really considered this before, but fascinating nonetheless.
>
> Wonder if this would affect the moment of a pendulum.
>
>    
For a spherical Earth with a spherically symmetric mass distribution the 
vertical gradient is around -0.3ppm/m.

For the real Earth with the situation is somewhat more complex:

http://gge.unb.ca/Personnel/Vanicek/MeanVerticalGradient.pdf

The period of a pendulum will vary with its height above the terrain.

Bruce





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