Which way water swirls

Tornadoes are too small to be affected by the Coriolis force and spin in any direction. The spinning direction of drain water is random, determined mostly by how the water is bumped, sloshed, or distributed when it starts to drain.

Topics: Coriolis force , angular momentum , drain , drain direction , draining water , hurricane , swirl in drain. Hurricanes are large enough to be affected by the Coriolis force. Sinks draining water are not. Hurricanes spin counter-clockwise in the northern hemisphere. For any normal bathtub you are likely to encounter in the home, however, the answer is no.

Imagine a cannon fired southward from any latitude above the equator. Its initial eastward motion is the same as that at a point on the spinning earth. This initial eastward velocity is less than that at a point later in its trajectory, because points closer to the equator travel in a bigger circle as the earth rotates. Therefore, the cannon shell is deflected westward to the right , from the perspective of a person standing on the earth.

A gunner firing a cannon northward would find that the shell is also deflected toward the right. These sideways deflections are attributed to the Coriolis force, although there really is no force involved--it is just an effect of being in a rotating reference frame. The circulation directions result from interactions between moving masses of air and air masses moving with the rotating earth.

The effects of the rotation of the earth are, of course, much more pronounced when the circulation covers a larger area than would occur inside your bathtub.

Even in a tub having a perfectly symmetric drain, the circulation direction will be primarily influenced by any residual currents in the bathtub left over from the time when it was filled.

It can take more than a day for such residual currents to subside completely. If all extraneous influences including air currents can be reduced below a certain level, one apparently can observe that drains do consistently drain in different directions in the two hemispheres.

Finally, Thomas Humphrey, a senior scientist at the San Francisco Exploratorium, discusses in more detail the reasons why we do not see the Coriolis effect at work in the bathroom:. For a fee, they will allegedly demonstrate that the toilets flush in opposite directions. It is only for show, however; there is no real effect. Yes, there is such a thing as the Coriolis effect, but it is not enough to dominate the flushing of a toilet--and the effect is weakest at the equator.

Coriolis acceleration at mid-latitudes is about one ten-millionth the acceleration of gravity. Because it is a very small acceleration, it needs a very long distance for it to produce an appreciable curvature--and hence directionality--to the motion. There you have it. Another myth, going down the Skip to content Site Navigation The Atlantic. Popular Latest. The Atlantic Crossword.

Sign In Subscribe. The Simpsons episode " Bart vs. Australia ," which involves the oldest Simpson kid getting indicted for fraud in the Commonwealth, starts with a scene in a bathroom. Bart has noticed that the water in the sink always drains in a counterclockwise way; Lisa informs him that, in the Southern Hemisphere, it drains the other way. Bart doesn't believe her. To find out for sure, though, he calls a number in Australia—collect—and … hijinks ensure.