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Bathtub vortex

  1. Oct 21, 2011 #1
    Is it true that bathtubs in northern hemisphere the water drains out in clockwise rotation and those in southern hemisphere in anticlockwise direction?
    If so then why?
    And in equator?
     
  2. jcsd
  3. Oct 21, 2011 #2

    DaveC426913

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    False. A big honkin' stinky myth that just will not die.

    Snopes has a good description of this silliness.
    http://www.snopes.com/science/coriolis.asp

    Frankly, I think even they are too generous. They talk about it as a "miniscule" force that is "easily overwhelmed" by larger forces.
    Unfortunately, this getting-a-foot-in-the-door caution leads people to "...OK but a perfectly symmetrical bowl filled with reeeeeally still water would - in theory - still exhibit blah blah blah..."

    Do this thought experiment.

    Pick up a bucket of water. Hold it still.
    Over the course of ten minutes, rotate it 2.5 degrees - a turn of about two centimeters.

    That's less than 2cm over ten minutes. That's how much torque is applied to the water by the Earth turning. Now, the 10 seconds it takes for a toilet to drain is 1/60 of that - 300 micrometers - on the order of the width of a human hair.
     
    Last edited: Oct 21, 2011
  4. Oct 22, 2011 #3
    Wikipedia details the lengths necessary to observe the Coriolis effect in draining water:
    http://en.wikipedia.org/wiki/Coriolis_effect#Draining_in_bathtubs_and_toilets
     
  5. Oct 22, 2011 #4

    Danger

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    If I ever had a toilet that took more than 15 minutes to flush, I would have to install at least 2 more bathrooms in my house. In any practical situation, the hemispheric influence is unmeasurable.
    You could also counteract any such Coriolis effect by training your turds to curl in the opposite direction and thus redirect the fluid flow.

    At the equator, the water just hovers over the drain because it can't make up its mind.
     
    Last edited: Oct 22, 2011
  6. Oct 22, 2011 #5

    DaveC426913

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    And I now have my weekend project!:tongue2:
     
  7. Oct 22, 2011 #6

    Danger

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    Keep it fair too, Dude. You're not allowed to swallow a Bratwurst whole.
     
  8. Oct 22, 2011 #7
    My earth science teacher in high school specifically taught us that the toilet water spins due to the coriolis effect. When they teach it in school, I'm not surprised the myth keeps going.
     
  9. Oct 22, 2011 #8

    Danger

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    Yeah... I couldn't figure out why my Grade 12 chemistry teacher was such an idiot until about 10 years later when I found out that once you have your degree in Education they assign you to what you will teach, whether or not you know anything about it.
     
  10. Oct 22, 2011 #9

    HallsofIvy

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    Most states (in the United States, specific requirements for teaching are set by the state and so vary from state to state), a secondary school teacher must have an undergraduate degree in the subject, with a minor in education. Of course, once they are teaching, they may be assigned by the principal to teacher a course in different area. Too much of that can cause trouble with the school's accreditation.

    In the elementary grades, teacher's typically have degrees in education.
     
  11. Oct 22, 2011 #10
    Never mind that vortex. The best myth I heard in that area was that this same force determines... the direction your cat wraps its tail around when sitting! I always knew cats are neat and picky but THAT picky? Hmm.
     
  12. Oct 22, 2011 #11

    Danger

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    That is true, and very irritating. Normal cats are ambidextrous, so they don't care. Mine is dyslexic, so she just stands there whipping it around until she get too tired and falls over.
     
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