ISEN-ASTC-L is a service of the Association of Science-Technology Centers
Incorporated, a worldwide network of science museums and related institutions.
*****************************************************************************

Okay, for one last piece, try <http://www.pasco.com> and there search for:
"doppler rocket" (product WA9826) and there you will be able to download
and both watch and listen to this foam football with a sound source on
board being propelled back and forth in a novel way. All that I have
previously said about a tossed football still applies so the demo does not
give you the perspective of someone that the moving source passes by. You
will see how a trolley system is inadequate for the task of speeding the
source along in a convincing way, since you need something on the order of
10m/s for a vehicle speed. All of my responses to this thread have been
based on my own actual experiences, including this one. I have actually
used the Dopper Rocket, and it is quite fun. A deep understanding of the
Doppler PRINCIPLE still needs work with wavefronts, either before or after
the audio fun.

Tom Ford

At 10:50 AM 8/14/04, 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.
>*****************************************************************************
>
>I agree with most of what Tom is saying on this but I still think it's
>worth messing about with sound demos. Here's another idea which may or may
>not work: If you have a fairly large auditorium (we don't) string a loop
>of tight wire from the front to the back with two pulleys, one at the
>front and one at the back. (The whole thing should be like an old-time
>laundry line used in tenements.) and attach a little "car" holding a horn
>to this wire. Then use the pulley at the front of the room to move the car
>quickly to the back. My guess is that this would do quite nicely, at least
>for those sitting more or less in line with it.
>
>By the way, I saw a re-creation of the original train experiment on a PBS
>show years ago where they had a group of trumpeters standing on a flatcar
>being pulled by a steam locomotive of the era. The whole "band" played a
>set note (I think "A") and proceeded down the track past the observer. All
>the time the whole ting was very well explained. You might want to contact
>PBS to see if you can track this video down. It was fun and great!
>
>John Bowditch
>
> > ----------
> > From:         Tom Ford
> > Reply To:     Informal Science Education Network
> > Sent:         Friday, August 13, 2004 9:49 AM
> > To:   [log in to unmask]
> > Subject:      Re: doppler shift demo
> >
> > ISEN-ASTC-L is a service of the Association of Science-Technology Centers
> > Incorporated, a worldwide network of science museums and related
> institutions.
> >
> *****************************************************************************
> >
> > The context of the original question was related to celestial observations
> > and (ordinarily) we don't listen to the stars! I have already posted
> > sufficiently with respect to the doppler interpretation of wave fronts. If
> > the discussion is now restricted to audible demonstrations for large
> > audiences, I have to agree with William that most of the demonstrations are
> > unsatisfactory in that they are confusing for a neophyte audience, even
> > using the demo he proposes. A major difficulty is that the effect is not
> > uniform for all observers in a typical classroom or auditorium and that has
> > to do in great measure with the distance the moving source is from the
> > observer. A foam football with a sonalert and battery is a help if there is
> > time to listen to everyone be the passer and the receiver.  A sound source
> > moving directly toward or away from the observer conveys the best
> > information. If the sound source is passing the observer, the time it takes
> > for the up-doppler to become the down-doppler depends on the passing
> > distance. For my students, this was a common task to calculate and graph
> > this for an assortment of speeds and distances.
> >
> > The most satisfactory endeavor evolved from an original attempt to record
> > the doppler shift of an automobile horn. It happened that this gave good
> > results on the approach only. When a separate 500Hz horn was rigged with a
> > switch to plug into the cigarette lighter socket, a passenger could keep it
> > aimed out the window at the stationary observer at the side of the road who
> > similarly kept the microphone aimed at the vehicle. Driving by at different
> > constant speeds and different passing distances gave data that could be
> > actually analyzed on a computer back in the classroom and compared with the
> > student graphs. My point here is that the recording itself was an excellent
> > demonstration tool, even without the analysis. If I were doing it again
> > today, I would do it with a digital video camera instead of just an audio
> > tape. This would make it easier to clean up the recording for analysis and
> > the playback would be more self explanatory. Asking people to "remember"
> > something they might have witnessed is dangerous to proper concept
> > formation, but using this form of playback would enable all listeners to
> > witness the same thing at the same time and be guided to distinguish>
> > between changes in intensity (sound doesn't have "volume") and changes in
> > frequency or pitch.
> >
> > Tom Ford
> >
> >
> > At 10:22 AM 8/12/04, 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.
> > >***********************************************************************
> ******
> > >
> > >Unfortunately a number of classroom-sized doppler effect demos (for
> > >after-the-fact demonstrations) aren't that accurate.
> > >For example I recall the aluminum rod demo where the teacher moves his arm
> > >(with the singing rod) forward and backwards.  In that one, most people
> > >will buy that it's a pitch phenomena (because that's the topic you're
> > >talking about) unless they really have an ear for pitch in which case they
> > >will realize that the pitch doesn't change noticeably - what does
> change is
> > >the volume.  The primary factor there is actually one of volume (the speed
> > >you can move the rod forward with your arm isn't that appreciable, and if
> > >you leave your hand extended forward it still basically sounds the same).
> > >  However, using a rotational motion you can achieve substantial
> velocities.
> > >  If you really want to see if the doppler effect is achieved, use a sound
> > >source that clicks - you should hear the clicks coming more rapidly or
> less
> > >rapidly depending on the item's motion.  With a lecture hall/auditorium,
> > >you could arrange for a device to fly overhead with such a
> sound.  Everyone
> > >knows of the changing sound of a motorcycle, and can relate to that
> > >wavelength change partially because it doesn consist of clicks that turn
> > >from a whine to a low pitched clicking sound.
> > >
> > >-William
> > >
> > >William Katzman                    "The important thing is to never stop
> > >questioning." -A. Einstein
> > >Director of Exhibits               "Are you sure about that Al?" -His
> wife.
> > >Catawba Science Center
> > >ph: (828) 322-8169 x307
> > >fax:(828) 322-1585
> > >[log in to unmask]

***********************************************************************
More information about the Informal Science Education Network and the
Association of Science-Technology Centers may be found at http://www.astc.org.
To remove your e-mail address from the ISEN-ASTC-L list, send the
message  SIGNOFF ISEN-ASTC-L in the BODY of a message to
[log in to unmask]