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Re: Waves (was ...Chichenitza...)



At 11:38 7/9/00 -0700, Richard Hake wrote:

... go the great Phys-L Listserv archives at
<http://mailgate.nau.edu/archives/phys-l.html>, click on "Search the
archives"
...
1. Search the archives of a list before asking a question or opening
a new topic (it may already have been discussed ad nauseam).

10. Use a brief signature which includes your affiliation, mailing
address, and (if you have one) your homepage.


Richard Hake, Emeritus Professor of Physics, Indiana University
24245 Hatteras Street, Woodland Hills, CA 91367
<rrhake@earthlink.net>
<http://www.physics.indiana.edu/~hake>

This valuable clue from Richard on accessing the list search facility
immediately yielded this note from Kyle F on the ascending chirp
at Chichenitza.

*******************************************************

Date: Mon, 10 Jan 2000 10:47:42 -0500
From: kyle forinash <kforinas@IUS.EDU>
Subject: dispersion at Chichenitza

I...was able to visit the ruins at
Chichenitza. While there I was able to hear...
a kind of dispersion effect for sharp
sounds made directly in front of the great pyramid. If you clap your
hands about 30 to 50 meters away while standing directly in front of
the stairs there is a distinctive chirp in the echo; lower sounds
return faster creating an echo that rises in pitch....
kyle
-----------------------------------------------------
kyle forinash 812-941-2390
kforinas@ius.edu
Natural Science Division
Indiana University Southeast
******************************************************************
Compare the note above with my observation from last night (below).
The geometry is almost identical: the position of the impulse
generator is similar (40 meters vs. 150 ft. estimated).
The position of the listener is different: Kyle was at an oblique
angle from the array of steps, I was almost in the plane of the
array of furrows.

********************************************************************
...
These artillery shells set off a propellant charge and then
explode in a star burst at one or two hundred feet. ...
Each shell first lifted off and banged with a shower of stars, and
then there was a distinct sustained echo at a few hundred Hertz...
much lower than the 2 kHz note
...was the diffraction grating due a ploughed field(?)

... The note lasted perhaps 2 seconds or less, and
descended one or two semitones in the first half second, then held on
the lower note.
This was another possible indicator of some geometrical effect of
ground interference, I suppose.

**************************************************************

The juxtaposition of these two observations makes it clear to me,
that Kyle could possibly have heard a descending tone from close
to the foot of the pyramid, while I could have heard an ascending
tone if stationed in a high tower adjacent to the shell burst.

I take the view that the frequency dispersion in time is geometry
dependent for these two cases.

brian whatcott, independendent student
<inet@intellisys.net>
Altus OK