It’s the first thing that many tourist do when visiting the southern hemisphere. Right after departing their flight, they hit up the nearest bathroom to watch the water flush down the “wrong” way. However, many people have little understanding of what causes this “weird” phenomenon.
The Coriolis Effect
When traveling in an airplane, you might not realize, but you can actually see the earth slowly rotating. However, if someone were to look up at that same airplane, it would appear to them as though the plane was seemingly diverging off course. What is happening here is an example of the Coriolis Effect. The plane is traveling straight, however because the earth is rotating beneath the plane, we have a skewed perception and the plane’s path appears to be curved.
The Great Toilet Debate
One of the biggest misconceptions associated with the Coriolis Effect is that it causes the rotation of water down the drain of the sink or toilet. This is actually not the reasoning behind the flow of water in your toilet or sink. The water itself is simply moving too fast down the drain to allow for the Coriolis Effect to have any real impact.
Though the Coriolis Effect does not influence the movement of water in a sink or toilet, it does have an impact on wind, the ocean, and the Earth’s winds. Even though in Australia and the rest of the southern hemisphere, toilets often spin counterclockwise, but the flow isn’t strong enough to notice.
In the end, the Coriolis Effect is caused by the Earth’s rotation, and only has an influence on very large objects or forces, such as hurricanes or tornadoes. Water draining from a toilet, sink or bathtub is too small to be impacted by this natural phenomenon, but it isn’t out of the question. The bowl design and the direction of the water flow going into the toilet determines the rotation direction as it is flushed.