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In my experience, the audible doppler shift is best used as a TERMINAL
activity. The best INITIAL demonstration needs to be one that sets a deep
conceptual basis for a new understanding, not just a label that can be
recalled. The basis for the phenomenon needs to be pictured in terms of
wavefronts from which wavelengths for various observers can be readily
seen. I know of two ways of showing this that have been successful. One of
them is to use a ripple tank where a periodic point source is moving with
respect to the water. This can be projected in various ways for the benefit
of viewers, but the best way to appreciate it is within arms reach of the
apparatus. Another way, which can also be projected on an Overhead
Projector, is to gather three or more macrame hoops of incremental sizes.
When these are positioned concentrically. they represent the "right now"
position of wave fronts that were generated periodically by a stationary
source in a stationary medium. If the centers of the hoops are positioned
evenly along a number line, the hoops represent a doppler pattern as it
might be seen by an observer in front, behind, or anywhere else. The wave
barrier is portrayed by stacking all the hoops to have a common point and
beyond that the shock wave possibilities can be easily explored. I refer to
these two means of illustration as the wet ripple tank and the dry ripple
tank. Fundamental to an understanding of the doppler effect would be an
appreciation of the apparent wavelength as seen by the observer. It is the
wavelengths that are measured in the case of stellar spectroscopy. In the
case of the audible examples, the wavelengths are not perceived, only the
frequencies are heard and the analogies must be carefully drawn..
Tom Ford
At 10:39 AM 8/11/04, you wrote:
>ISEN-ASTC-L is a service of the Association of Science-Technology Centers
>Incorporated, a worldwide network of science museums and related institutions.
>*****************************************************************************
>
>for a workshop about finding extrasolar planets, I am looking for a
>convenient way to demonstrate Doppler shift. (An intern of mine told me
>how cool it was when her science teacher demonstrated it to them by
>driving by the school with his horn blaring -- not feasible, sorry)
>
>The obvious thing is some sort of constant-tone noisemaker whirled around
>on a string - but in a small (10m/33ft) room, and with a lot of elderly
>docents running things, this doesn't seem like a good idea.
>
>Of course, I could depend on their experience, but to have a concrete
>example would be best. Any suggestions?
>
>Marc Taylor
>Coordinator, Andrus Planetarium
>Hudson River Museum
>511 Warburton Avenue
>Yonkers, NY 10701
>(914) 963-4550 x223
>Fax: 963-8558
>[log in to unmask]
>
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