Re: standing waves

[Tom Ford <tomford@THESCIENCESOURCE.COM>]

It has been pointed out that for a good fork, higher modes (not harmonics)
will quickly damp out. How the fork is made (home-made is fun on the school
milling machine) and where it is struck and with what it is struck make all
the difference. An interesting low-tech exploration can be done with nested
tubes that can be quickly adjusted. Similarly an array of slightly
different quarter-wave resonance tubes (tube with a sliding styrofoam plug)
can be used for the exploration, including end corrections in the
calculations. Try hard and soft hammers on different parts of the tine.
Vernier's LabPro/LoggerPro combination is a favorite tool for this and
other acoustical investigation. In this way, one can see the struck tine
teach the other tine what to do and what two forks do just before they
settle down to a consistent beat. A picture on the screen is worth a LOT of
words when it comes to making waves.
Tom Ford

At 12:45 PM 4/17/02 +0200, you wrote:
> Hello,
>
> I have question on standing waves. I have undestood that standing wav=
> es
> (fundamental and higher harmonics) are produces on any object that is=
> set onto
> vibration. Then I read from a high school physics book that a tuning =
> fork would
> have only one frequency and no higher harmonics at all.
>
> Well, I checked one tuning fork using a microscope and oscilloscope. =
> The signal
> was quite sinusoidal but it was altered significantly. To me it looke=
> d like an
> interference between the fundamental frequency and harmonics. Perform=
> ing a
> Fourier analysis could separate the signal into components but I do n=
> ot have
> that possibility at school.
>
> Could it be that a tuning fork minimizes amplitudes of higher harmoni=
> cs and
> that's why the book stated that only one frequence is produced?
>
> Regards,
>
> Antti
>
> Antti Savinainen
> Physics Teacher
> Kuopion Lyseo High School/IB
> Finland
>
> Homepage: <http://personal.inet.fi/tiede/physics/>