Re: Waves

[Stan Dodds <dodds@RICE.EDU>]

David Abineri asks

> Am I correct in explaining string instruments, to say that a string
> actually vibrates in many modes simultaneously when bowed or plucked?
> That is, is it producing its fundamental along with several harmonics
> all at the same time?

Yes. The relative intensity of the harmonics is determined by the
excitation conditions and the nature of the instrument. That's why a
violin and guitar sound different when playing the same note, and why
a plucked violin string sounds different than a bowed string. (The
sound you hear is also influenced by the various resonances of the
instrument body, of course.)

> Is it possible to show this behavior (if the notion is correct) with a
> string vibrator or other equipment, rather than just postulating to
> students that this does in fact occur?

You could try plucking a simple string at various points and listening
for different 'tone quality'. Or get a student to demonstrate with a
plucked vs bowed violin. If you have CBL equipment, a microphone
and Fourier Transform software would show differences in the
spectrum. (Your students don't have to understand the FT. Just
demonstrate how the display relates to changing pitch, and remind them
of the graphic displays on some music systems.)

There is lots more information in musical acoustics books, but perhaps
this will help you get started. It's a really good topic for a general
physics class.

Stan