Natural Science Forum / Earth Science / Oceanography / July 2006

I am pleased to find that I am not the only person on the planet that
has a scientific view of the so called Coriolis Effect. The following
is in reference to small bowls draining:

"...centripetal accelerations in any observed spiraling motion cannot
possibly come from the tiny Coriolis force from the Earth's rotation.

Water does not go down the drain differently in Auckland than it does
in Santa Fe. In order to demonstrate the Coriolis force in this
experiment one must have a very shallow sink, and tiny drain, so that
water drains over a time period comparable to a fair fraction of a
day."

It is a combination of pressure gradient in the volume of liquid and
the degree of neutrality of the resevoir that permits the formation of
an helical vortex at the plug hole. The water at the top of the bowl
has more acceleration than that at the bottom, so is preferentially
drained.

This explains why the funnelling needs some time to get set up.
Rotation takes place because at the eye of the vortex the resultant of
dynamic forces is neutral. The pressure of falling water is the same in
every direction.

It is this pressure that allows the wall of the funnel to form. Any
predilection to rotate in a certain direction is therefore due to some
other force. Something like a seiche effect, or in the case of a bowl
of water, a vibration in the housing.

And so onto the observed absurdity of hurricana. The writer seems to
have dropped the ball here:

"Extratropical cyclones are the big weather systems of the winter
season. They have a scale (L) of about 2,500 km, a typical wind
velocity of 10 m/sec, and the Rossby number is R_o = 0.04 or so.
Obviously a Rossby number so small means that the Coriolis force is
much greater than the observed centripetal acceleration, and some
additional force is needed to maintain the observed curvature of
motion. These systems are dominated by Coriolis force balancing mainly
a pressure gradient."

http://www.sas.org/tcs/weeklyIssues_2005/2005-06-03/feature2/index.html

But back to the small resevoir:

"The speed of sound depends of two parameters:  the stiffness of the
medium, and its density.  Very stiff materials transmit sound rapidly.
But sound travels more slowly in dense materials, because, given the
same force, heavier things are harder to accelerate than lighter
things. It turns out that the speed of sound is proportional to the
square root of the stiffness (Young's modulus) of the medium divided by
its density."

http://www.sas.org/E-Bulletin/2004-04-02/feedback/index.html

The more dense a material the more difficult it is to transmit sound.
And the more flexible the material the more likely the material is to
absorb it. But when a vortex funnel forms as a liquid drains the
pressure on the water changes subtly.

Of course this is nothng in comparison to the changes made to the
ability of the liquid to oscillate once the volume starts to fall. But
it is interesting that once the volume starts to fall, it falls faster.

Thus funnels form as a result of vibration and tension. And their
relationship to seismic activity may be seen in the fact that as an
harmonic reaches a certain geologic feature, the pitch changes and a
certain wavelength can be observed.

This is work ascribed to Bernard Chouet who analysed the pitch of
seimic waves and found long period events:

"Chouet said they were made by molten magma resonating - that is coming
under pressure - inside the volcano. The more long period events there
were, then the nearer the volcano was to exploding. Chouet could use
the long period events to predict an eruption to within days."

http://www.bbc.co.uk/science/horizon/2001/volcanohell.shtml