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[Phys-L] Re: Singing Rod Demo....



on 11/25/05 5:15 PM, von Philp at vonphilp@MYACTV.NET wrote:

Some other physics teacher and I were recently debating the singing rod demo
where an aluminum rod resonates after stroking it with fingers rubbed in
rosin.

The debate was about whether the standing waves created were transverse or
longitudinal. My gut feeling is the waves are longitudinal based on the
manner in which the metal rod is stroked. Another teacher strongly believed
that the waves must be transverse because the impressive volume of the sound
is too great to be achieved longitudinally.

What do the rest of you think? Is there a compelling test or evidence to
prove what type of wave it is?

Thanks,
Ralph von Philp
Ralph,

I used to have students determine the frequency of vibration by whatever
method the wanted to use than have then determine the speed of the wave. A
quick look in the CRC Handbook and they could determine the type of wave and
their accuracy. The CRC lists three wave speeds for Al but they are widely
separated so it is easy to choose. Just for fun note that were you strike
the side of the rod you generate a wave which degenerates quickly,
relatively speaking, into the wave that is generated by striking the end of
the rod.

Carl
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