[time-nuts] Non electrical time-nuttery

[J. Forster]

> namichie at gmail.com said:
>> The reason that I remember a hard vacuum is not used is because the
>> low pressure is used to rate the pendulum (fine tune) by slightly
>> increasing or decreasing, and in a hard vacuum metals tend to weld
>> together and oils evaporate so the mechanical bits seize up.
>
> How does the pressure change the frequency?

I don't think it does.

> Why are oils a problem?  I thought typical pendulums used a spring rather
> than a bearing.

I think a torsion pendulum suspended by a fiber woul have no oil to be an
issue.

> That does raise an interesting issue.  How would you fine tune a pendulum?

A back-and-forth pendulum is tuned by adjusting it's active length. If
it's suspended by a flat spring, you can adjust the spring length,
adjusting the period.

With a torsional pendulum you could also adjust the spring rate or the
wheel moment of inertia with symmetric radial screws.

> If you can get close enough, then you can tweak things by varying the
> amplitude, or temperature.

I don't think that's a good idea. With a back-and-forth pendulum amplitude
adjusts non-linearity. A good pendulum should be temp independent.

> Big Ben is tuned by adding/removing a penny from the pendulum.
>   http://en.wikipedia.org/wiki/Big_Ben  (search for penny)
> That technique gets more interesting in a vacuum, but you might be able
to rig up something equivalent.

Effectively changing the pendulum length by moving the CG relative to the
pivot point.

-John

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