The Misappliance Of Science

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The Drain in Spain

Debunked: Bathtubs and toilets drain the other way round in the other hemisphere, due to the Coriolis Force.

The Coriolis Force, named after French mathematician Gustave Gaspard Coriolis, is the name of the inertial force applied to moving objects within a rotating coordinate system, that appears to deflect the object's direction. It is most observable on Earth in winds and ocean currents, if you're measuring such things.

Because meteorological and oceanic phenomena show Coriolis influence regarding their direction of rotation, people who can't ordinarily observe such events like to believe that Coriolis can be observed on a small scale, such as with bathwater draining out of a tub. This is impossible.

On such small bodies of water, there are local forces at work that have vastly more influence over the behavior of the water than the Coriolis force. Still water in a home bathtub is in fact not still enough to be free of more powerful motions that would obliterate any Coriolis influence. Placement of the drain in the tub, the shape of the tub, thermal currents: these and many other things will overwhelm the influence of the Coriolis Force.

In the case of toilets, the direction that water is jetted into the toilet will determine the rotation of the toilet draining.

True: The Coriolis Force affects all fluids if you take incredible pains to isolate it.

If a small body of water is isolated from all external forces such that its internal motion is slower than one rotation per day, you could observe Coriolis influence on that water. The level of isolation required is unachievable in a typical home.

References:

• The Urbanlegends.com archive of Coriolis Force references