Why toilets flush in different directions

It is an interesting sidelight that when back on the bus, he informed his fellow tourists that they had just witnessed fakery the Earth did not cause the rotation they had just seen there was widespread disappointment. The tourists preferred the fantasy to the reality. Fraser proceeds to explain how you can fake it yourself. According to various sources , it is possible to demonstrate a Coriolis effect on water on a small scale, but only under extremely controlled circumstances -- involving predictably shaped water vessels, long periods of time of waiting for water to become as still as possible, carefully removing a stopper in the bottom of the vessel without adding spin, and other such crazy stuff.

But in your typical toilet or sink, the Coriolis force is so small as to be undetectable relative to other forces. Even holding a bowl of water and turning around introduces sufficient spin to get things going in one direction or another.

Go to your bathroom now and observe water going down the drain -- any drain you want. Depending on the efficiency of your plumbing, you may need to stop up the drain, fill the basin, then unplug it and wait. It might also help to have something lightweight floating in there, to mark any motion -- a few bits of tissue may work, or a matchstick or two. Observe whether the draining water forms a clockwise or counter-clockwise spiral.

Go ahead, I'll wait. Now check all the other drains you can find. Do they match? In my admittedly unscientific testing just now, one sink drained clockwise, the other counter-clockwise, one didn't have an easily observable spin it's small , and the toilet was also counter-clockwise, clearly due to the position of its water jets. There you go: science in action. Via Steven Frank , via Snopes. 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. A toilet or sink is just not large enough.

The Coriolis effect influences because wind velocities may be hundreds of times greater than the motions in a sink and because the distances involved are far larger than the tiny draining diameter in a sink or toilet. The net motion in the water becomes much more pronounced as the water is forced to move in toward the center of evacuation, causing the normally invisible flows in the water to become visible as the water nears the drain.

The ultimate direction of that flow is random--it can go one way one time, the other way the next. But you will find that the faucet is almost always off center or that there is some other asymmetry in the sink. As a result, filling the sink consistently gives it some net rotation in the same direction, which you see as the normal direction of evacuation.

In , Ascher Shapiro, an expert in fluid mechanics at the Massachusetts Institute of Technology who died in , ran an experiment showing that the Coriolis force does affect water drainage, but the rotational effect is so small that it's overshadowed by other factors, such as the direction that water enters a basin or the shape of the basin which is a function of how the toilet-maker designs the bowl and flush mechanism. Shapiro began his experiment by filling a large, shallow dish with water, making sure that the water entered the dish with a clockwise swirl, the opposite direction you'd expect it to turn in the Northern Hemisphere.

He covered the dish with a plastic sheet, which removed any air drag, and let the water stand for 24 hours to negate its initial spin. When Shapiro first unplugged a drain at the bottom of the dish, he didn't notice any rotation to the water as it drained.