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Q & A: Toilet Water

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Most recent answer: 10/22/2007
Q:
My friend and I were, taking about toilets, I don’t remember why, but I added that I heard in the southern hemisphere the water spins in the opposite direction from the Northern Hemisphere. I remember hearing this when I was kid, but couldn’t find any resources to explain and didn’t have the funds to travel to Australia to do some scientific experimentation. Could you confirm that this is indeed the case and let me know why exactly this happens. Thank,
- Brian Moore (age 25)
Burlington, VT
A:
Brian -

The way that the water in your toilet swirls is determined by the way that your toilet is built, not which hemisphere you live in. The toilet shoots the water into the bowl at an angle, which determines which way the water swirls.

What you may have been thinking of, though, is the way that water swirls when it drains out of your sink or bathtub. Old science textbooks did say that this is different in the Northern vs. Southern hemispheres. Unfortunately, this is one of the many cases where you can't always believe what you read.

The reason that the old books gave is the Coriolis effect, which has to do with the way that the Earth rotates out from under something that moves freely. (You can picture this by imagining a cannon that sits on the equator and fires straight North. As the planet rotates out from under it, the cannonball will appear to veer to the right, or go clockwise. If the same cannon were to be fired straight South, the ball would still appear to veer to the right, but it would be moving counterclockwise with respect to the ground.)

However, this effect isn't strong enough on water to actually determine which way the water will swirl. (It's a nice theory, though.) There are far too many other things that can effect it, like the slight pre-existing movements of the water.

-Tamara

(published on 10/22/2007)

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