On a Season 6 episode of The Simpsons entitled “Bart vs. Australia,” Bart and Lisa are squirting toothpaste down the sink (see video below). The kids notice that the water circles counter-clockwise down the drain which Lisa claims is due to the “Coriolis Effect.” Furthermore, she says that water always drains counter-clockwise in the Northern Hemisphere and drains clockwise in the Southern Hemisphere.
Bart is skeptical and tries to prove his sister wrong. He calls a boy in Australia to disprove this theory and after hours of making the child flush toilets , admits his defeat. Toilet water flushes in different directions in the Northern and Southern Hemispheres.
Only one problem: this is a common plumbing myth.
The Coriolis Effect
First of all, the Coriolis Effect is misrepresented in the episode. What Lisa says is based on fact, but not actually factual.
All things being neutral, water will in fact drain counter-clockwise in the North and clockwise in the South due to the rotation of the earth. But this only happens in perfect conditions, such as a flawless tank in a room that is entirely still; the conditions that can only be met in a laboratory. If there are any imperfections in the tank, movement in the water, or other extra-ordinary conditions, then those can be blamed for the water swirling in the reverse direction.
So if the Coriolis Effect does not cause the water to drain a certain direction, what does?
Solution: Jet Streams
When you flush the toilet, water is sprayed out of jets just below the rim that are facing the same direction. These determine which direction the water flushes and can be pointed counter clockwise or clockwise, regardless of what hemisphere you live in.
As for your sink, well it drains based on outside factors, such as slope of the room and interference from outside objects, like rinsing your hands.
Although “Bart vs. Australia” is one of the best episodes of The Simpsons, the basis of the episode is fictional. No matter what hemisphere you live in, the toilet company decides what direction your water drains, not the Coriolis Effect.
Watch “Bart vs. Australia” below. The argument between Lisa and Bart occurs right after the opening credits, 22 seconds into the episode. Enjoy!
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