Coriolis Force and Water 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. And, of course, the rotation of the frame is only about 1° every forty minutes (360° per day). There simply isn't a lot of opportunity for deflection to happen!
    Quantitatively, putting these numbers into the equation on the main page 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. So, say it takes 20 seconds for a sink to drain, the water is totally unmoving when you start, and there's nothing else to mess with your results. It might be rotating at 1/180th of a degree per second when it finishes draining, ignoring conservation of angular momentum. If the drain is 1/100th as wide as the sink overall, you're still getting less than a degree per second rotation down at the drain. Nothing you'd ever notice.
    Under extremely controlled conditions (as were established in the work done in the references on the main page), 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 more than enough to overwhelm the small contribution of the Coriolis effect in your kitchen sink or bathtub.
    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 at the Equator!). Maybe there's a conspiracy to manufacture right-handed sinks and toilets 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.

Back to the Main Coriolis force Page.