:-)

[link|http://www.physics.ohio-state.edu/~dvandom/Edu/newcor.html|Getting Around The Coriolis Force]:

5.2. Water Going The Wrong Way Down The Sink

In a kitchen sink, of course, speeds and time scales are much smaller than hours and miles. 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 Equation 1 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 effect can be observed1,2.

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 effect shown at tourist traps along the Equator (especially since east/west deflection is absent!). 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 effect unless your sink is the size of a small ocean.


Even if it goes the other way down under, that doesn't mean it's due to the Coriolis effect (or, in other words, due to the Earth's rotation). It's not - the Coriolis effect is too weak in a sink or toilet unless everything is carefully controlled.

HTH.

Cheers,
Scott.