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Re: dispersion at Chichenitza



Your last comment just clicked. I once wrote extensively on
reflections from washboard surfaces, correct - in part, as it turned out -
an earlier paper by Rayliegh (Annals of Physics (NY) about 1958).
The reflection pattern is very complicated, to say the least,
but the directions of the maxima of different frequencies are
grating-like.
Regards,
Jack

Adam was by constitution and proclivity a scientist; I was the same, and
we loved to call ourselves by that great name...Our first memorable
scientific discovery was the law that water and like fluids run downhill,
not up.
Mark Twain, <Extract from Eve's Autobiography>

On Mon, 10 Jan 2000, kyle forinash wrote:

At 10:47 AM 1/10/00 -0500, kyle forinash wrote:
there is a distinctive chirp in the echo; lower sounds
return faster creating an echo that rises in pitch.
...
Does anyone know exactly how this works?

If you had reported a sound that *falls* in pitch there would be a
beautiful explanation. It would be a great demonstration of
diffraction-grating physics.

It pretty much sounded like a rise to me (but no one said I have
perfect pitch!). The first half of a wolf whistle.

If I had stood in one spot and heard only the low notes coming back
and then heard high notes at a different location I would have said
diffraction. But I didn't move. I don't see how diffraction changes
the speed of return. Dispersion does this but I don't see why the
steps cause dispersion.


You don't need to travel to the Yucatan to observe acoustical
diffraction. Any building with exterior lattice-work on a sufficiently
coarse scale will do nicely. Actually most such buildings are nicer than
pyramids, because they give you more options as to the angle of incidence.

===========

If you really are reporting a sound that *rises* in pitch I have no idea
what is going on.
-----------------------------------------------------
kyle forinash 812-941-2390
kforinas@ius.edu
Natural Science Division
Indiana University Southeast
New Albany, IN 47150
http://Physics.ius.edu/
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