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December 18, 2003
"And water always flows out the drain in a clockwise direction....?"
actually, it's supposed to be anti clockwise and then only in the northern
hemisphere, but it is a fallacy - water rushing down a drain flows at
speeds on the order of a meter per second in most sinks, which are
themselves less than a meter wide. Qualitatively, there doesn't seem to be
much chance for deflection. Quantitatively, putting these numbers into the
equation for the Coriolis force
F = -2 m (w x vr)
results in an estimated change in rotation of only a fraction of a degree
per second, and a very small fraction at that...less than an arc-second
(1/3600th of a degree) per second over the course of the entire draining of
the sink, ignoring additional effects caused by conservation of angular
momentum and the like. Under extremely controlled conditions, this can
cause water to flow out of a container counter-clockwise in the northern
hemisphere and clockwise in the southern hemisphere, but your kitchen sink
is not so controlled. Things like leftover spin from filling the sink (even
when the water looks still, it's rotating slowly for a long time after it
seems to stop), irregularities in the construction of the basin, convection
currents if the water is warmer or colder than the basin, and so forth, can
affect the direction water goes down the sink. Any one of these factors is
usually more than enough to overwhelm the small contribution of the
Coriolis effect in your kitchen sink or bathtub. Research in the 1960s
showed that if you do carefully eliminate these factors, the Coriolis force
can be observed.
Water in the sink doesn't go far enough to trigger a noticeable
north/south deflection. Most often, it simply spirals down the sink the way
it went into the sink, and the same is true of things like the famous
"demonstration" of the Coriolis force shown at tourist traps along the
Equator. Maybe there's a conspiracy to manufacture right-handed sinks in
the Northern Hemisphere and left-handed sinks in the Southern Hemisphere?
In any case, don't blame it on the Coriolis force unless your sink is the
size of a small ocean.
(Google for Coriolis effect for more of this!)
Regards
David
"David Jacobs" < davidj@... > 27677
Posted on December 18, 2003 07:54 PM
Posted to category(s) Cooling System | Engine (external)
