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[Phys-L] Re: Foucault pendulum



I am disappointed that nobody has been able to see through the analysis
of a continuous AC pendulum drive.
As far as I recall, there is a speed of crossing the axisymetrical
electromagnet which provides an advantageous impulse to the pendulum
bob.
The appropriate crossing speed is associated with an appropriate
amplitude, sure enough - so that the period is as always controlled by the
pendulum's length, but the amplitude is conditioned by the drive frequency.

It is quite possible that the impulse is insufficient to drive the pendulum
(or maintain it) at the appropriate amplitude, in which case it will subside.

This is the magic behind this method....

Brian Whatcott

At 01:41 PM 11/14/2005, you wrote:
What you want is a clock pendulum drive. They are very inexpensive and
do not modify the period as determined by the pendulum. The Sci. Am.
article's may be the same as the commercially available one. The only
problem I see is the commercial drive expects little drag; a huge, in
comparison, pendulum, especially w/ a spherical bob instead of s
lenticular one, will have too much drag. However, I suspect it will be
easier to add a stronger drive than begin de nuovo.

bc

p.s. My friend, the horologist, is an old hand at custom designing such
things, and may be of assistance. However, he is not subsidized as an
academic, and therefore, unless it is especially interesting won't want
to spend much time w/o compensation.


http://www.bmumford.com/clocks/

Brian Whatcott wrote:

At 07:59 AM 11/14/2005, John Suhl, you wrote:


Brian's suggestion of a simple AC circuit is interesting but I wonder
about phase issues and keeping the pulse period exactly the same as
the pendulum's period. I'll look up the articles in Sci. Am.

Still open to circuit ideas.

Thanks.

John

- - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
John E. Sohl, Ph.D.


The constant AC drive method uses line frequency.
The method depends on the balance of force as seen from
the pendulum's bob. The desired condition is a little more pull to
the center while approaching than when leaving the center.

The method is extremely frustrating to folks who want to take
care of transients and feedback from a sensor to a drive...
There is no sensor - only the time varying magnetic field in the
vicinity of the coil.


Brian Whatcott Altus OK Eureka!



Brian Whatcott Altus OK Eureka!
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