> [email protected] 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 =============== _______________________________________________ time-nuts mailing list -- [email protected] To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
