John Rumm wrote:
Guy King wrote:

The message
from John Rumm contains these words:

The hot chocolate effect discussion neatly snipped (by other(s).)

Any other explanations you can think of?

Change of speed of sound in the fluid. That should affect the resonance
much as breathing helium affects the pitch of your voice.

Yup - that could certainly be the case... you would probably expect to
detect a pitch change with temperature as well then as the density of
the liquid changes.

Rotation of the fluid in the container. Particularly if the fluid is

The other problem with rotation based theories is that I tend to stir side
to side rather than by inducing rotation. You still get the same effect.

What would really help would be having a name for the phenomenon to make
it easier to find other research.

I believe it is called the "hot chocolate effect":
http://www.sas.org/E-Bulletin/2004-0...ack/index.html

I tried to engender a discussion on the subject once:
http://groups.google.com/group/sci.g...1cc2037b081d0e

But of course that was in a couple of scientific newsgroups so there
were no takers.