What Hemisphere You Are in Does Not Affect the Way Water Spins Down Your Drain

coriolis effectToday I found out what hemisphere you are in does not affect the way water spins down your drain.

So why do some textbooks, most tour guides, and pretty much all TV shows like The Simpsons get it wrong?  The myth that water in your drain will spin differently depending on what hemisphere you are in primarily stems from taking a very real physical precept, namely the Coriolis Effect, and applying it to a situation that it doesn’t make sense with.

The Coriolis Effect, named after Fustav Gaspard de Coriolis (1792-1843) who published a paper in 1835 on the subject, is basically an apparent force relative to the Earth’s surface that causes objects to appear as if they are moving in somewhat of a curved path. What’s actually happening is they are moving straight and it is the Earth turning that makes it look like they are curving.  So more practically, it causes apparent deflection of moving objects to the right in the Northern Hemisphere; to the Left in the Southern Hemisphere; and no apparent deflection on the equator.

Northern Hemisphere KittehSo it seems reasonable enough to think that the Coriolis Effect would affect the way the water spins down the drain.  Indeed, things such as hurricanes and other large cyclonic systems are very much affected by the Coriolis Effect in terms of which way they spin.    However, a hurricane might literally be 500 miles in diameter and last for many days;  your sink or toilet is very small in comparison and the time the Coriolis Effect has to influence the draining water is very small as well.  In fact, when we are talking draining sinks, toilets, and bathtubs, the size and time scale is so small that the Coriolis Effect force is practically non-existent in terms of effecting the water in any way, especially when compared to the other forces in play here like the shape of the sink, the way the jets are pointed in the toilet, and things of this nature.

In this case, the Coriolis Effect has about the same affect on the swirling water in your toilet as a butterfly’s wings flapping have on a Tornado.

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  • you… are…an…idiot…
    have you ever been south of the equator?
    When I lived in New Zealand, I observed this very effect.
    once again….
    you… are…an…idiot…

    • It’s an engineering issue not a gravity or natural force variant. Most manufacturers of toilets in the US use a similar model for toilet design so that the release of water over the curved bowl surface creates a cyclonic motion to better clean away, well you know.

      Different countries with different manufacturers of toilets will have different types of flush. So a different release path for the water or a variant in the design and curvature of the bowl can change the outcome of the direction the water takes.

      For example, when I lived in Germany in the 90’s The toilets jetted straight to the drain and there was nothing swirreled at all due to the larger drain hole at the bottom of the bowl.

      SOOOOOOO…If you are going to call someone an IDIOT. Be sure you yourself can clearly and astutely articulate the argument you are getting into. In other words…please be nicer!

      HEGALIAN THOUGHT: Thesis –> Synthesis <–Anti-Thesis

      AND FINALLY: Most of the times problems are overthought!
      I.E. Need to find a needle in a haystack, BURN DOWN THE HAYSTACK!

      OH, and I may be completely wrong…please prove it!

      • It is amazing to me how sombody can be so kind and patient in case of answerimg such a crasy and dumb man.
        Thanks Kevin, I have to learn this important thing from your great manner.

  • I teach high school Earth Science, and used to teach that the water rotated differently in the hemispheres. Until one day I decided to test the theory in our own ladies room of the school. Guess what? Two out of the six toilets had water that rotated counter-clockwise, while the others rotated clockwise. THEN I actually researched the Coriolis Effect (instead of just blindly teaching potentially bad science)and had to apologize to my classes. It did however turn in to an excellent lesson on debunking myths.

  • Hi from Australia. I concur with Jim – the water DOES rotate the opposite direction when going down the drain here.

  • Daven Hiskey

    @jim: sometimes personal experience can fool you, particularly when it comes to physics and things of this nature. Check this out: http://www.snopes.com/science/coriolis.asp

    If you still aren’t convinced you can look at the mathematical explanation and see that the Coriolis Effect affects the water in your drain a few orders of magnitude less than the combined other forces in your drain; so again, like a butterfly’s wings flapping against a tornado: http://en.wikipedia.org/wiki/Coriolis_effect

  • I live very close to the equator, and have seen how water swirls indifferent directions when the plug is pulled 20 m to the south and 20 m to the north of the equator. Believe it or not, precisely on the equator, the water goes straight down the plug! You probably won’t believe me, but I have seen it demonstrated several times.

    • Notice a logical comment was ignored by the “math” guy. There is a few you tubes showing this exact same statement you posted.

  • Wow!!! I can’t believe this. Daven, you say that it is so. Just that it would be very hard to observe. So why even say that it isn’t true? Jim may actually be overstating your intelligence. If you are going to hold that a certain result will occur you should not clearly relate opposing facts.

    • Daven Hiskey

      @John: The water will swirl the way the jets are pointed or with how the sink is shaped vs. how the water enters it and other such factors. The Coriolis effect isn’t strong enough on this scale and time-span. It has about the same effect as you waving a hand fan at a tornado. Feel free to read up on the math behind it to see just how little force the Coriolis effect has on this scale/time if you don’t want to take my word for it.

  • Gidday. I’m from Oz & I’ve been watching water spin clockwise all my life.
    However. I made a point of observing during visits to England and Germany.
    The water spun in the anti-clockwise direction.

    Despite the Coriolis effect being debunked. Is this the only explanation ?
    There is much we don’t know about water & we probably wouldn’t build damns if we knew more.

    Surely human anecdotal evidence counts for something.

    With all due respect, I say it’s true and the answers probably won’t be found in a maths book.

  • all those who are saying it’s true seem to be ignoring all the variables that account for the different directions the water goes ie. what daven has already stated; the direction the jets are pointed, the shape of the container etc. etc. Listen….. physics has already proven that the hemisphere you are in has nothing to do with the which way your water drains, so if you want to continue believing in things that have already been disproven, enjoy your time at sea, because your going fall off the edge of your flat world!! But the good news is, as your falling you can finally swallow all the gum you want, because you wont have to worry about it taking 7 years to pass through your system!!!!

  • lol @ jim …
    it is amusing how many people are not able to acknowledge the fact that something they believed in their whole lives is proven (by science, math and logic) to be not true at all. and we’re talking about stupid, pointless thing as direction of water spinning in drains.. now try to talk some sense into religious people.

    • WOW Helinka! I thought you were going to add something of value to the conversation but it appears to me that you just wanted to throw a dagger into the beliefs of people of faith. Well, I don’t know about the beliefs/faith of others but I am a believer in JESUS CHRIST who is GOD THE SON in the triune God head of the Christian faith and HE is the Creator of this universe. It’s okay to believe in science, math and logics to a great extent, but… until that “intelligence” can explain which came first… the CHICKEN or the EGG… and I won’t mention all the other plants and animals (inclusive of MANKIND) who had a “beginning” somewhere…, then the people of faith appear to have as much and probably more sense than those whom you deem qualified to speak to us. Said all of that to say… you can’t offer what you don’t have… don’t try to talk sense into us… try to get some first. Now my thoughts concerning the direction of the water in the toilet… I’m just glad when it flows down and fulfill it’s purpose.
      I’d like to invite you to read the Bible and pray that GOD would reveal Himself to you. Grace and Blessings be unto you.

  • I tried this out in my bathroom and I live in the northern hemisphere. The shower water spins clockwise, but the toilet and sink spin counter-clockwise. Case closed for me.

  • It seems the problem people have with accepting this explanation is very similar to the problem they have with global warming. Eg. “But we had a really cold winter this year – and the last one” or “I don’t notice it getting any warmer – global warming must be a myth”. Scientific experimentation trumps individual, one-off, small sample experience – if we can’t trust science on these questions it becomes every man/woman’s opinion for themselves. I’ve got the humility to accept when data proves me wrong – I hope most other people do too.

  • Nope. The coriolis effect can indeed affect the direction of angular momentum in draining water.

    Unlike clapping in a tornado or the flap of a butterfly wing in a hurricane, water draining in a sink is an amplifier of angular momentum.

    The tiniest angular momentum differential between opposite sides of the drain will become amplified by the the inertial component of spin. Spin influence becomes cumulative and amplified. And self-sustaining.

    You can observe this yourself when you see that water spinning around the drain spins so fast that centrifugal force holds the water up against the sides of the toilet bowl and inhibits draining. That causes a slowdown of spin and re-establishes drainage, but now a balance is reached and maintained, where spin and drainage is maintained at a steady rate until all the water is gone.

    Among other things, this means that – yep, Coriolis effect, however slight, does influence the spin direction of draining water in the hemispheres.

    Coriolis effect also makes flushing toilets marginally inefficient. Too much water is wasted going around in circles around the bowl when it should be flushing stuff straight down the drain.

    • Daven Hiskey

      @Bananas: And your sources for this are?

    • There is no such thing as “centrifugal force,” and no one who really understands physics or engineering uses the term. Centripetal force, or angular momentum, is demonstrated by a centrifuge, which is how this semantic error came into being; but this phenomenon does not make basin drainage less efficient.

  • im a fith grader and at my school we are doing an expimernt abot this and i wrote my report then i cheacked this again and forgot to look at the reviews and turns out i wrote a great report on the WRONG FACTS THANK YOU

  • When I went to Ecuador on vacation I visited the actual center of the world (not the one with the big monument, which is off by some 200 meters). There they had a plain metal bowl with a hole in the middle. The people there would pour water into the bowl and pull the plug. On one side of the Ecuador (can’t remember which), a spiral would form clock-wise. Doing the same exercise on the other side of the Ecuador, a spiral would form counter clock-wise. When the bowl was placed on the Ecuatorial line, the water would pour from the bowl straight down with no spiral at all. I saw this happening various times. No jets on a toilet, no forces pushing the water in one direction or another, just a plain bowl, with a hole in the bottom, still water, the plug was pulled from the bottom, so not to disturb the water.

    • Daven Hiskey

      @Lao: The problem with that is that even if you were many thousands of miles on one side of the equator or other, the math just doesn’t work out. Being just slightly on one side of the other, makes it even drastically less likely as the forces involved to make something like that happen are for all practical purposes, equal. If you don’t want to take my word for it, and the math quoted, feel free to Google around. This is a very well known myth and has been thoroughly debunked by scientists the world over.

      • Davin your wrong. Every touist has seen it work on the equator. Just go on you tube and look it up there are numerous videos posted from around the world. When you use the exact same sink and remove the drain plug where there is no other forces other the gravity the water will go cw or ccw or straight down depending on where you stand.

        • Daven Hiskey

          @Alex: Certainly, what do scientists know? I’m sure you’re right and all the physicists are completely off on this one. 😉

      • If the math doesn’t work out, then your math is bad. This is basic science (that which you seem to reverently respect but do not understand) in that when your observations don’t match your predictions then you have to re-examine your predictions. You don’t just say that the observations are wrong.

  • Look guys, doubting is a fantastic thing to do, but there is a point where doubting turns into burying your head in the sand.

  • i would d love to see a video of the guy in Ecuador do the experiment

  • Of all the articles on this website (terrific, by the way), what sparks the most heated debate? Flushing toilets. Go figure…

  • It is amazing that people still discuss this in 21st century. Don’t we switch to figure out why bean spiral up in one direction?

  • I agree that the phenomenon may be real, but the reason given by science is simply a guess. In all honesty we don’t know a whole heck of a lot. About all science does is come up with a story that sounds good, that’s it.

    • Daven Hiskey

      @russ fleenor: The reason given by science is not at all a guess in this case. Science is actually all about not guessing, but finding the truth of things.

      • While you are correct that Earth rotation had no effect on flushing or draining average tubs in the bathroom, You are incorrect that the Coriolis effect can not be observed as affecting draining water differently in the 2 hemispheres. In controlled experiments eliminating all other external factors the Coriolis effect can be shown; however it could never be a factor in an actual setting because of all the variables present. Robert Ehrlich, a physicist at George Mason University explains it in several articles if you care to read them.

  • Toilets are too “explosive” for this. As already mentioned, they are engineered to send crap away as fast as possible (without making a mess), so the water jets are pointed such to do make the vortex to pull the stuff away.
    So the actual experiment should be done with a big deep bow with a drain stopper. Fill it with water (or similarly very fluid stuff), let it rest for some time, and pull the plug.
    Go to the south and repeat…..
    Bonus: in this internet instant communication with a friend on the opposite hemisphere should be a big helper.

  • This article is an interesting experiment in language, specifically tone. If you write something authoritatively enough in tone (set aside facts for the moment) and then claim you have math (the science says so), then any number of people will believe you. The fashionable way to do this is to make the claim “what you’ve always known is wrong.”

    Youtube has plenty of demonstrations of the effect that this article disclaims. Toilets are a bit of a strawman since they force the water in one direction or another. The coriolis effect may in fact be like a butterfly flapping its wings in a tornado comparatively, but it’s still observable by the naked eye in a sink or other container.

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