SCIENCE

Which Way Does Your Toilet Flush? Investigating The Coriolis Effect 'Down Under'

06/03/2015 12:07 pm ET | Updated Jun 03, 2015

There's more than one way to flush a toilet.

In fact, as this pair of videos from YouTube science gurus Dr. Derek Muller and Destin Sandlin illustrates, there's two. You just have to be in opposite hemispheres for it to happen naturally. And it helps if your toilet is actually a kiddie pool, but we'll get to that.

Press play on both of these videos at the same time. If your mouse-clicking fingers aren't that fast -- and who could blame you? -- there's another way to do it: Set the video on the right forward 18 seconds by clicking 18 seconds forward on the timeline, and pause it there. Next, press play on the video on the left. When it hits 18 seconds, press play on the first video. They don't have to be perfect, but it helps.

The pools in the above videos drain in opposite directions thanks to the Coriolis effect, the phenomenon caused by the spinning of the Earth, which also impacts everything from the rotation of hurricanes to the swirl of body hair (OK, there's not much evidence for this one, though it's plenty amusing).

Toilets -- like kiddie pools -- are beholden to the Coriolis effect, too. In theory, the same toilet would flush in opposite directions in opposite hemispheres, but in practice, since toilets direct the water flow within the bowl, they flow in the direction they're designed to. They're also so tiny that they don't feel the Coriolis effect on a large scale.

According to Dr. Paul Doherty, senior scientist at the Exploratorium in San Francisco, gravity is 30 million times more significant than the Coriolis effect in describing how water travels down a drain. Which doesn't mean the Coriolis effect isn't visible, only that lots of other external factors have to be minimized for it to appear.

"For household sinks, tubs and toilets this is a myth," Doherty told The Huffington Post in an earlier article on the Coriolis effect. "People can check it for themselves. Drain all the sinks and tubs in their house and see which way they swirl. Usually some sinks would drain clockwise and some counterclockwise, which means either it is a myth, or they live on the equator."

But as the two videos above illustrate, once outside factors are controlled for, the Coriolis effect does indeed hold water.

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