Hi! Thanks for such an interesting question.
This is what is called by some as an example for the Coriolis force
BUT according to most experts THIS DOES NOT APPLY to the explanation
of the rotation of water draining in your sink.
?Don't believe what you hear about Coriolis making the water in a sink
or toilet rotate one way as it drains in one hemisphere, the other way
in the other hemisphere. The Coriolis force is noticeable only for
large-scale motions such as winds.?
USA Today: ?Understanding the Coriolis force?
?Is it possible to detect the Earth?s rotation in a draining sink??
?Yes, but it is very difficult. Because the Coriolis force is so
small, one must go to extraordinary lengths to detect it. But, it has
been done. You cannot use an ordinary sink for it lacks the requisite
circular symmetry: its oval shape and off-center drain render any
results suspect. Those who have succeeded used a smooth pan of about
one meter in diameter with a very small hole in the center. A stopper
(which could be removed from below so as to not introduce any spurious
motion) blocked the hole while the pan was being filled with water.
The water was then allowed to sit undisturbed for perhaps a week to
let all of the motion die out which was introduced during filling.
Then, the stopper was removed (from below). Because the hole was very
small, the pan drained slowly indeed. This was necessary, because it
takes hours before the tiny Coriolis force could develop sufficient
deviation in the draining water for it to produce a circular flow.
With these procedures, it was found that the rotation was always
?Explanations are funny things. Indeed, what do you mean by suggesting
that the difference in behavior is a result of the difference in the
(underlying) velocity. Let?s start by ignoring the fact that you
thought (incorrectly) that the issue was just the easterly component
of the velocity and just explore the difference between these two
situations: the large scale with a big velocity difference and the
small scale with a small velocity difference. The implication is that
if one were to match the velocity differences on the two scales, then
the Coriolis force, or maybe the displacement, would suddenly be the
same in each case. Alas, it would not be so (unless other things were
?The traditional response to what you have suggested is that you have
confused two things, a spatial scale and temporal scale. As usually
presented, the Coriolis force (being a force) produces a result (such
as displacement) over time. The spatial scale (how far it is across
something, or how far an object travels) does not even appear in the
equations. There is much to commend this approach. Within this
context, it is not the spatial scale that produces the effect (for a
given force), but how long the event lasts. A sink drains quickly (not
much time for a small force to produce a significant displacement); a
missile or the air in a hurricane takes much longer to traverse its
territory (a much longer time for a force to produce a significant
?Bad Coriolis FAQ?
Ascher Shapiro of MIT demonstrated this in 1962 with the following experiment.
?All this was demonstrated way back in 1962 by one Ascher Shapiro, a
researcher at the Massachusetts Institute of Technology. Shapiro
filled a circular tank six feet in diameter and six inches high in
such a way that the water swirled in a clockwise direction. (Remember,
now, that Coriolis forces in the Northern Hemisphere act in a
?Shapiro then covered the tank with a plastic sheet, kept the
temperature constant, and sat down to read comic books or whatever
scientists do while they wait for their experiments to percolate. When
he pulled the plug after an hour or two, the water went down the drain
clockwise, presumably because it still retained some clockwise motion
?On the other hand, if Shapiro pulled the plug after waiting a full 24
hours, the draining water spiraled counterclockwise, indicating that
the motion from filling had subsided enough for the Coriolis effect to
take over. When the plug was pulled after four to five hours,