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

Daven Hiskey July 23, 2010 24
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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24 Comments »

  1. jim July 23, 2010 at 12:02 am - Reply

    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…

  2. Maribeth July 23, 2010 at 12:05 am - Reply

    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.

  3. Geoff July 23, 2010 at 12:06 am - Reply

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

  4. Daven Hiskey
    Daven Hiskey July 23, 2010 at 12:10 am - Reply

    @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

  5. sophia July 23, 2010 at 5:05 am - Reply

    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.

  6. John July 23, 2010 at 12:24 pm - Reply

    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
      Daven Hiskey July 23, 2010 at 3:45 pm - Reply

      @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.

  7. Trex July 23, 2010 at 11:45 pm - Reply

    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.

  8. Fabio! July 25, 2010 at 7:37 pm - Reply

    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!!!!

  9. halinka July 27, 2010 at 4:56 pm - Reply

    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.

  10. misterpold July 30, 2010 at 2:20 pm - Reply

    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.

  11. BlackNarcissus October 20, 2010 at 5:18 pm - Reply

    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.

  12. Joe Bananas December 5, 2010 at 6:08 pm - Reply

    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
      Daven Hiskey December 5, 2010 at 9:29 pm - Reply

      @Bananas: And your sources for this are?

  13. Jack January 18, 2012 at 2:39 pm - Reply

    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

    • Daven Hiskey
      Daven Hiskey January 18, 2012 at 3:24 pm - Reply

      @Jack: If you wrote that what hemisphere you are in does not affect the way water spins down the drain/toilet, than you wrote the correct facts. :-)

  14. Lao September 18, 2013 at 5:10 pm - Reply

    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
      Daven Hiskey September 18, 2013 at 8:38 pm - Reply

      @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.

  15. Akane January 22, 2014 at 12:51 pm - Reply

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

  16. Thomas Smith January 23, 2014 at 11:43 am - Reply

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

  17. joka March 3, 2014 at 1:36 am - Reply

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

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