Re: Steel Bar Music aka "singing rods"

[rogerk@maxwell.phys.csufresno.edu (Roger Key)]

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 listserv@appstate.edu.

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."         *
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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
email: rogerk@csufresno.edu    http://maxwell.phys.csufresno.edu:8001
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