Folks,
Actually, the USGS goes around measuring the local gravitational constant
in various places. There was a gravimeter set up in the basement of one of the
local universities a few years back doing just that. And some time ago, the
U.S. spent a fair amount of time, money and effort (presumably as did the
Soviet Union and others) mapping the Earth's external gravitational field to
correct for its effect on ballistic missile trajectory. Probably still do.
Francis
On Dec 12, 2011, at 5:19 PM, Magnus Danielson wrote:
> On 12/12/2011 01:37 AM, Jim Lux wrote:
>> On 12/11/11 4:04 PM, Tom Van Baak wrote:
>>
>>> GCPC -- gravity controlled pendulum clock (elevation)
>>>
>>
>>
>> intriguing. From your parenthetical remark, I'm assuming you move the
>> whole assembly up and down to adjust the speed?
>>
>> I was thinking about a huge mass that moves around?
>>
>> let's see.. period is proportional to sqrt(1/g)
>>
>> g is proportional to 1/r^2, so period is proportional to r.
>>
>> Earth is roughly 7000 km radius, so moving it 1 meter higher or lower
>> changes the period by 1part in 7million... interesting.
>
> Hmm... how does the near-field gravitational pull behave?
>
> The far-field is surely r^-2, but wonder about the near-field effect.
>
> Need to grab some paper and pen and convince myself.
>
> Cheers,
> Magnus
>
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