Sorry guys but the Simpsons have done this already !!!!
Who Knew?
by Louis-Benoit Desroches
(view PDF)
Do you remember that episode of “The Simpsons”—the one where Bart calls collect to Australia to determine if the toilet drains clockwise or counterclockwise? Lisa explains that water drains in the opposite direction in the southern hemisphere because of the Coriolis force. Later, the Simpsons discover a toilet in the US Embassy, which drains in the “American” way thanks to hardworking technology. It is a funny episode and one of my personal favorites. Unfortunately, it makes no scientific sense.
The Simpsons, great icons of popular culture, are propagating a terrible misconception about the role of the Coriolis force that is so prevalent, we all seem to share it. If you’ve ever stared at your toilet while repeatedly flushing it (not that exciting, I must warn you), you probably noticed that it only drains in one direction, reinforcing the notion. The Coriolis force is not the culprit, however.
The Coriolis force is a pseudoforce, much like a centrifugal force, resulting from a rotating coordinate system (i.e. the Earth as it spins). Inez Fung, professor in the Department of Earth and Planetary Science and director of the Berkeley Atmospheric Sciences Center, explains that as the Earth rotates, a person standing at the equator moves in a larger circle than someone at higher latitudes, and thus moves faster. A pocket of air moving northward from the equator would therefore “gain” on the Earth below, resulting in an arced path that drifts eastward. Similarly, a pocket of air moving southward from the Arctic would “trail” the Earth below. This east-west pseudoforce is what we call the Coriolis force. It is responsible for many atmospheric effects including the spiral patterns of hurricanes, as surrounding air is funneled into a central low-pressure zone. “What is relevant,” says Fung, “is the time and distance traveled.” Storm systems develop over several days and travel hundreds of kilometers. Your toilet draining lasts ten seconds and is (hopefully) confined to a foot-wide bowl. Fung points out that a sky diver doesn’t need to account for the rotation of the Earth below because the Coriolis force is simply too weak on such quick, small-scale events.
So why does your toilet always drain in the same direction? There are other factors that far outweigh the Coriolis force: the symmetry of the bowl’s shape, the direction that the water jet flows when you flush, and the location of the drain. Any of these mundane details can determine which way the water drains. Despite what you’ve heard on “The Simpsons”, you won’t need to travel to Australia to find an oppositely draining toilet. A quick peek in your neighbor’s bathroom might be enough (though you should probably ask first).
lol, don't worry mate, we've all done it
