[Physltest] [Phys-L] Re: 'Seeing' frequencies above 30-40Hz (fwd)

[James McLean <mclean@GENESEO.EDU>]

Scott Goelzer wrote:
> Ludwik reminded me of a neat demo done at Lowell Regional Physics
> Alliance, but I cannot remember the name of the demonstrator or source
> of demo.
>
> Tuning fork had a bit of mirror mounted on the top of one fork and was
> set vertically on rotating turntable. A laser aimed at the mirror
> reflected a nice sine wave on the wall as the fork rotated and
> vibrated.

I'm not sure I understand the configuration.

The best I can understand this, I'm imagining that the mirror is at a
45deg angle to the turntable radius, and the laser is aimed almost
tangentially to the turntable, so that the laser only reflects off the
mirror for a relatively small fraction of the rotation:
    __--__
   /      \   turntable from above
  /        \
|        /-------->
  \       |/
   \__  __|
      --  |
          |
        laser

But I'm still not sure how this would work, since the primary motion of
a tuning fork tine is towards/away from the other tine, which would not
result in vertical deflection of the laser beam.  Maybe the flexing of
the tine along with the optical lever is enough?

Is this the right configuration?
--
Dr. James McLean                     phone: (585) 245-5897
Dept. of Physics and Astronomy       FAX:   (585) 245-5288
SUNY Geneseo                         email: mclean@geneseo.edu
1 College Circle                     web: http://www.geneseo.edu/~mclean
Geneseo, NY  14454-1401
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