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There is a common myth that water flowing out from a sink should rotate in direction governed by on which hemisphere we are; this is shown false in many household experiments, but how to show it theoretically?

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I would go about this by computing the magnitude of the Coriolis effect in a typical sink drain and comparing it to other effects that might change the direction of the drain, e.g. some tilt in the sink or faucet. – j.c. Nov 2 '10 at 20:32
Exactly what @J.C. said. Other factors, namely the angle of the sink's axis relative to gravity and how the water enters the sink or bowl. – Mark C Nov 22 '10 at 18:07
By the way, congratulations, MBQ! – Mark C Nov 22 '10 at 18:14
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@Mark For breaking 1k? Thanks. Now its time to make some edits [-; – mbq♦ Nov 22 '10 at 20:35
Yes, I like to be the one to give the "deciding" vote. – Mark C Nov 22 '10 at 23:06

1 Answer

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The calculation of the Coriolis force is dependent on latitude:
$F = m a$ where $a = 2 \Omega sin(lat)$, with $\Omega$ being the Earth's angular velocity
$m$ is the mass of the object in question

The Earth's angular velocity is (about) $7.29 \times 10^{-5}$ rad/sec

So, for a sink with a couple gallons of water in it at 45 degrees north... the Coriolis force is about $7.57 \times 2 \times 7.29 \times 10^{-5} = 1.10 \times 10^{-3}$ N.

Interesting reading about this over this way, and (of course) here.

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The Coriolis force is dependent on velocity. You can't get it just from the latitude. – Mark Eichenlaub Mar 29 '11 at 12:45

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