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Re: Cryogenics Bat



Bill (and the rest of the phys-l and sci am club lists)
Just a quick note to let you know that one of my students (Kori
Valz, Shenandoah Valley Governor's School) has, in fact, done the
suggested experiment. Details at 11.

The bad news first: the tuning forks used were aluminum alloy so
the results may not be valid for the musical instrument types. We will
repeat this in the spring sometime with different forks.

The forks were analyzed using a microphone hooked up to a PC
running Cool Edit 96 (a program which I use in the Sound portion of my
Physics course and recommend). The FFT was a triangular one with size
65536. The 16 forks (one full octave (256 - 512 Hz) x2) were measured
x5 before, quenched in liquid nitrogen for 1 minute, measured
immediately (x5 @ 10 second intervals), remeasured x5 after the forks
came to room temperature (>2 hour), quenched again for 10 minutes in
liquid nitrogen and remeasured x5 after the forks came to room
temperature (>24 hours).

The results are still being analyzed but preliminary results
indicate that any permanent effect is small (<1 Hz). Note that she did
see that the frequency changed when the forks were cold (immediately
after quenching) and that the frequency continued to change as the fork
warmed. The frequencies were around 3-4% higher for each fork
immediately after quenching, and got lower as the fork warmed. After 2
minutes the forks were back within 1% of the original frequency.
(Condensation was a problem and was removed with a paper towel). After
two hours any effect was very small (< 1 Hz). The quenching for ten
minutes appears to produce about the same results when the forks were
tested after 24 hours (any effect < 1 Hz).

Thanks for the suggestion and we thought that you ought to be in
on the results.


THO

Thomas O'Neill
o'neill@csvrgs.k12.va.us
Physics
oneill@csvrgs.k12.va.us
C Shenandoah Valley R Governor's School


-----Original Message-----
From: William Beaty [SMTP:billb@ESKIMO.COM]
Sent: Wednesday, May 12, 1999 7:54 PM
To: PHYS-L@LISTS.NAU.EDU
Subject: Re: Cryogenics Bat

On Wed, 12 May 1999, brian whatcott wrote:

> Fitting a miniature spark plug in a mouthpiece, and capturing
the impulse
> response
> from a microphone capsule via an A/D sounds relatively easy to
set up.
> A kitchen piezo gas igniter could provide the spark. an
ordinary plotter
> shareware package offers FFT.... Now THERE's a science fair
experiment!

...or for a quick check, clamp two similar bits of metal in
small vises,
adjust them to give identical tones when plucked, then dip one
in LN2.
When the sample has warmed up again, has the resonant frequency
changed
as compared to the control?

Hey, I know! See if LN2-dipping can de-tune one of a pair of
identical
tuning forks. If whacked simultanously, any changes to their
beat-note
would be pretty obvious. If this demonstration gives large
results, then
it might be interesting to see how low a temperature is required
to achive
an easily-measured effect. What happens in a -30F freezer? Or
in a
dry-ice/alcohol bath? Does temporarily *heating* the treated
fork remove
the changes, or make them even larger?


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William J. Beaty SCIENCE
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