Toilet Bowl Trivia

You've probably heard that the spin of the earth causes toilet water to spin in a counterclockwise direction, but is it true?

The short answer: No. The long answer can be found below.

The premise of this popular toilet boil myth is based on something called the Coriolis force. The Coriolis force is the reason hurricanes spin in a counterclockwise direction in the northern hemisphere and clockwise in the southern hemisphere. To understand this, picture a merry-go-round on a playground. Now imagine, standing on one side throwing a ball to someone on the opposite side. Eventhough you throw the ball in a straight line, the spin of the merry-go-round causes the ball to curve on the way to its target. Now imagine spinning the merry-go-round the opposite way. The ball will still curve, but in the opposite direction. The earth works the same way.

Example: Air flows from high pressure to low pressure in the atmosphere. The air tries to flow in a straight line, but the curvature of the earth causes the air to curve to the right in the northern hemisphere and to the left in the southern hemisphere. This causes the wind to circulate clockwise around areas of high pressure and counterclockwise around areas of low pressure such as hurricanes.

Now that we understand the basic premise of the Coriolis force, let's revisit the merry-go-round experiment, but this time with a stationary merry-go-round. What happens when you throw the ball to your friend? Yeah, it goes straight to them. Shouldn't it curve due to the Coriolis force? Nah. See, the Coriolis is a large scale of motion, so it isn't detectable at such a short distance. A toilet bowl is much smaller than a merry-go-round, so there is no way the direction a toilet spins has anything to do with the earth's rotation.

So what causes toilet bowl water to spin? Well, I'm not toilet expert, but I would say it has much more to do with the direction the jets of the toilet are injecting the water into the toilet than it does the earth's rotation. Apparently, most toilets are built the same way.

The same holds true for bath tub drains. Being a science geek like I am, I've noticed that most do seem to spin in a counterclockwise direction. However, my house has 2 bathrooms and one of them spins in a clockwise matter. This proves by counter example that the Coriolis force has nothing to do with the way water travels down a drain--or your toilet.

What does this all mean? It means that this popular toilet bowl myth is worth no more than the stuff we flush down it.

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