Down the plughole (Was PBS show on Tornadoes...)
 

"Sir Jean-Paul Turcaud" wrote in message
...
Just take basic Physics 101, Fool !

The clockwise or anticlockwise spin in your bathtub drain is generated by
the De Coriolis forces .... and the subject is well documented indeed !

Err... no.

The "Coriolis force" is much too weak on these scales to have any effect on
this. Which way the water goes down the plughole is determined mostly by
the initial "swirl" you can hardly avoid giving it (and which is magnified
by angular momentum conservation as the water is drawn to the plughole) with
a possible contribution due to the shape of the bath.

I have heard stories of tourists who have visited equatorial countries being
amazed by demonstrations of vessels emptying through holes and the
"experiment" being repeated either side of the equator. Much as I hate to
spoil the local tourist trade, this is a conjuring trick using the principle
of the second sentence in the above paragraph, not a scientific
demonstration.

Even on the scale of the tornado (about three orders of magnitude greater
than that of a bath tub!) it is possible for local airflow to dominate the
Coriolis force and there are well-documented reports of "anticyclonic"
tornadoes in the literature. In fact the motion in a tornado is held in
balance by the pressure gradient force acting inward providing the
acceleration required to hold the rotating air in its circular path. Once
established, this works in either direction.

A hurricane is different. These *are* initially organised by the Coriolis
force and indeed cannot form very close to the equator because there is no
"spin" to start them going there. On this scale the principal balance is
between the Coriolis force and the pressure gradient force, but there is
still an extra contribution required from the pressure gradient to provide
the "circular path" acceleration, which is quite significant close to the
eyewall.
--
- Yokel -
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