The Coriolis effect is probably the most scientific excuse humans have for staring into toilet bowls. The effect makes objects on the Earth curve when they should go straight, and it's why some people insist that toilet bowls flush in the opposite direction on the southern hemisphere than in the northern hemisphere.
But if you've tried to make that happen when visiting Australia, you've probably been disappointed. So is the Coriolis effect real? Very. But toilets will lie to you every time.
Destin Sandlin, famous for his educational YouTube series Smarter Every Day, teamed up with fellow entertainer Derek Muller of the channel Veritasium to answer this question with what might be the coolest video project ever tackled on the Internet. It's up there, anyway.
The videos below are designed to be played in sync (there are some brief introductions and a countdown); fumbling with the play button is well worth the effort. The videos, unfortunately, can't lay side-to-side on our blog, which means missing out on a few visual tricks therein. We promise you'll still get a cool experience watching here, but if you really want the full effect, take a second to hop over to Sandlin's Web site, where he has them embedded the way he intended. Or, as Sandlin suggests, you can pull out your phone and hold it up to your computer screen, letting one video play on each. It's a brave new world.
So there you have it! The toilet myth is busted, but don't blame the Coriolis effect -- blame your toilet for being more powerful than the rotation of the Earth.
This effect is caused by the mismatched speed of the Earth's rotation: The equator is wider than the poles of the Earth, so points on the equator have to move faster to make one rotation in a day. If you threw something from the equator toward a pole, it wouldn't go straight, because the point you were throwing it from wouldn’t actually be moving at the same speed as the point you were throwing to. The ball would appear to curve while moving from point a to point b, even if those points were directly across from each other.
But the Earth rotates very slowly, indeed. On other planets, like massive Jupiter (which spins on its axis once every 9.9 hours) the same effect can be much easier to spot. Jupiter spins so fast that it has crazy-complex air circulation, with super-strong winds running in alternate directions. It gets its striped appearance from bands of dust with different compositions whirling in response to the planet's speedy rotation. And when those winds interact, they can form massive storms like the Great Red Spot, which is big enough to fit three Earths inside and has been raging for at least as long as humans have been looking at it (about 400 years and counting). On the other hand you have Mars, which rotates more slowly than the Earth and seems to exhibit an even weaker form of the Coriolis effect than we see at home.
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