Physics and Chemistry

Energy, Motion, and Force

Does water running down a drain rotate in a different direction in the Northern versus the Southern Hemisphere?

There is a widespread belief that water draining from a bathtub, sink, or toilet bowl in the Northern Hemisphere swirls counterclockwise while in the Southern Hemisphere the water drains clockwise due to the Coriolis effect. First described by the French mathematician and engineer Gaspard Gustav de Coriolis (1792–1843), the Coriolis effect is the apparent deflection of air masses and fluids caused by Earth’s rotation. Although it does have an effect on fluids over great distances or long lengths of time, such as hurricanes, it is too weak to control fluids on a small-scale, such as bathtubs, sinks, or toilet bowls. These can drain in either direction in both hemispheres. The direction is determined by numerous factors including the shape of the container, the shape of the drain, the initial water-velocity and the tilt of the sink.


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