There's no such thing as "the Coriolis force". It's the Coriolis effect, and
is only responsible for weather systems, and large scale fluid mechanics.
Not bath tubs.


"Road_Hog" wrote in message
...

"maxi" wrote in message
...
so there is no difference in the turning direction between the northern
and
southern hemisphere?

Yes, but as the reply said all other factors would have to be taken out of
the equation. In reality this doesn't happen.

"Bathwater should drain anticlockwise in the northern hemisphere,
clockwise
in the southern and straight down at the equator. This is caused by the
Coriolis force, a result of the earth's eastward rotation, which in the UK
causes water north of the plug to run to the western edge of the hole,
while
water on the opposite side of the plug moves to the eastern edge,
producing
an anticlockwise vortex. In Australia, the water should move in the
opposite
direction.
However, the direction of the vortex is easily disturbed by currents in
the
water, the alignment of the plughole, the shape of the bath, or water
temperature, so the phenomenon is difficult to observe."

And a little more detail.

"If you had a perfectly smooth bathtub in a perfectly round shape, and you
filled it full of water, let the water sit for a few days (to let every
last bit of turbulence from the filling of the bathtub die out), and then
let the water drain though a single hole in the middle of the bathtub,
then the water would begin to circulate (counter-clockwise in the northern
hemisphere, and clockwise in the southern hemisphere). This is exactly
what happens with weather systems. A low-pressure system is just like
this ideal bathtub - air is rushing in to the middle of the low pressure
system to try and fill the low pressure area, and water is rushing in
toward the drain to try and fill it.


However, bathtubs and toilets do not have these perfect shapes, and the
direction that the water circulates is determines by the shape of the
bathtub or by any turbulence that may be present from filling the bathtub.
The Coriolis forces are swamped by any minor imperfections.


It is possible to estimate the Coriolis forces in a bathtub. If we have a
bathtub at the North Pole (where Coriolis forces would be greatest, so
assume it is a hot tub so it doesn't freeze), and the bathtub is one meter
in radius, and the water drains from the edge of the bathtub to the drain
at the center in one second, then the deflection of the water will be less
than approximately 0.05 millimeters. This would be measurable, but is
rather tiny, and definitely nowhere near the circulation seen in most
bathtubs. A larger bathtub or a faster draining rate would amplify the
deflection.


In short, any "experiment" purporting to show the Coriolis effect in a
bathtub, toilet, or pan of water is a fraud, although not necessarily
intentional. But a glance at a satellite picture of clouds shows true
Coriolis effects without the need for a hottub at the North Pole!"



HTH









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