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Re: Steel Bar Music aka "singing rods"

I havn't seen too many replies on this so here goes ...

this is a demo which is described in Meiners book on physics demos,
and there are variations on this theme reported in AJP:

38(9), 1152 - regenerative feedback in a similar rod at fundamental f.
41(5), 734 - speed of sound in a similar rod
42(12), 1117 - speed of sound in a metal wire.

These references are from a bibliography (c) U of MN board of Regents.

the PIRA News also carried a short article on this last fall. More
discussion then took place on tap-l, at

Interesting to see that this may be another item that Ben Franklin
had his fingers in .... (smile)

I've also done this while walking down a street with a couple of other
people ... spotted a piece of electrical conduit (hollow pipe) about
a meter long and tried it - it worked - got some strange looks from
my companions that day though ....

- Roger Key

I first "learned" the singing rod demo from Fred Leitner at Rensselaer, but
it was also used as a lab exercise to measure the speed of sound in brass,
steel, and aluminum. A couple of hints:

Mark the rod using a file (whatever its length, but ~ 6' seems to work well
with all these materials) at intervals from each end 1/2, 1/3, 1/4, 1/5 its
length. Holding the rod at each of these will allow you to generate all
the harmonics as well as the fundamental. For odd harmonics, once
excited you can grab the rod at the center and the "other" node without
killing the sound. Pretty convincing standing wave demo! Beware of
neighborhood dogs responding to the call of the rod!

I've found that having rosin on thumb and forefinger works better than on
the palm, I suspect because you are trying to "excite" a smaller region of
the rod.

I haven't followed up in the literature to confirm this, but Fred Leitner
told me that the earliest reference to this demo was attributed to Benjamin
Franklin, perhaps in a letter to Lavoisier.
George Spagna ******************************************
Department of Physics * *
Randolph-Macon College * "Imagination is more important *
P.O. Box 5005 * than knowledge." *
Ashland, VA 23005-5505 * *
* - Albert Einstein *
phone: (804) 752-7344 * *
Internet: ******************************************

Roger Key Teaching Laboratories and Demonstrations
Cal. State University, Fresno Department of Physics
2345 E San Ramon Ave 209-278-2728 fax: 209-278-7741
Fresno CA 93740-0037 Pager 209-489-5977