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



Some more details recalled from several years back:
As I remember it the tuning fork was mounted vertically in a wood block
on a phonograph turntable. The mirror chip was mounted vertically also
on the top of one of the arms of the fork. Now that I think about it, I
will try putting mirror chips on both forks. The laser was set aiming
upwards at the mirror - a fairly shallow angle. The resultant sine
pattern was about 1 ft in amplitude and was sweeping across the top of
the room's walls. It does produce a surprisingly long horizontal
pattern, but did not completely pan the room. Optical levers never
disappoint. I can (would) check my notes, but they are back in the lab.

Scott
*******************************************
Scott Goelzer
Physics Teacher
Coe-Brown Northwood Academy
Northwood NH 03261
s.goelzer@comcast.net
*******************************************

On Jan 14, 2005, at 4:44 PM, James McLean wrote:

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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