Electrical Pendulum Drive (was Re: moon's synchronism)

[brian whatcott <inet@intellisys.net>]

At 11:51 3/20/98 EST, you wrote:
> ... any pendulum analogy would be like driving a steel
> pendulum bob on a long string whose natural period is 3 seconds at 60 Hz
> about its equilibrium orientation with an electromagnet.  In such a
> system the fact that we have a pendulum at all is quite secondary when
> describing the bob's high frequency vibrations.
>
> In conclusion, I don't necessarily recommend against using a pendulum
> analogy for this problem, but I do advise that it only be used with
> caution and with awareness of the significant limitations of the analogy.
>
> David Bowman
> dbowman@gtc.georgetown.ky.us
I found David's exposition exhilarating - as I often do.
  I note my regrettable tendency to pick on microscopic
blots in erudite academic pieces and so, despite the finer part 
of my nature I cannot resist remarking that a 60 Hz solenoid is 
found to be a viable (and delightfully simple) method of driving 
a Foucault's pendulum of period approaching 10 seconds. (*)

 So in a sincere symmetry, I note that cautions against using the
pendulum analogy should be made with an awareness of the unexpected
capabilities of driving it successfully with way-off-resonance forcing
frequencies.    :-)

Whatcott   Altus

Refs:
R Stuart Mackay, UCal, "Detecting the Earth's Rotation"
(*) (Professor) C.L. Stong, Book of Projects for the Amateur Scientist,
Simon & Schuster, 1960
 (and in fairness - R.S. Mackay in Am Journal Physics, 1953)