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# The "Think Test"

### #16 Major Payne Posted 02 February 2008 - 09:20 PM

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Actually, the water drain part was incorrect. It doesn't matter on which side of the hemisphere you are, the water is always going to drain clock-wise.

Wasn't talking about the sink drain and it was just a joke. The Coriolis effect does have an effect, but there are too many other factors that can change it so the sink drain is not the best model to use. Plus, it is a total myth:

A misconception in popular culture is that water in bathtubs or toilets always drains in one direction in the Northern Hemisphere, and in the other direction in the Southern Hemisphere as a consequence of the Coriolis effect. This idea has been perpetuated by several television programs, including an episode of The Simpsons and one of The X-Files. In addition, several science broadcasts and publications (including at least one college-level physics textbook) have made this incorrect statement.

Some sources that incorrectly attribute draining direction to the Coriolis force also get the direction wrong, stating that water drains clockwise in the northern hemisphere. If the Coriolis force were the dominant factor, drain vortices would spin counterclockwise in the northern hemisphere.

In reality the Coriolis effect is a few orders of magnitude smaller than various random influences on drain direction, such as the geometry of the container and the direction in which water was initially added to it. Most toilets flush in only one direction, because the toilet water flows into the bowl at an angle. If water shot into the basin from the opposite direction, the water would spin in the opposite direction.

When the water is being drawn towards the drain, the radius of its rotation around the drain decreases, so its rate of rotation increases from the low background level to a noticeable spin in order to conserve its angular momentum (the same effect as ice skaters bringing their arms in to cause them to spin faster). As shown by Ascher Shapiro in a 1961 educational video (Vorticity, Part 1), this effect can indeed reveal the influence of the Coriolis force on drain direction, but only under carefully controlled laboratory conditions. In a large, circular, symmetrical container (ideally over 1m in diameter and conical), still water (whose motion is so little that over the course of a day, displacements are small compared to the size of the container) escaping through a very small hole, will drain in a cyclonic fashion: counterclockwise in the Northern hemisphere and clockwise in the Southern hemisphere—the same direction as the Earth rotates with respect to the corresponding pole.

Ron
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### #17 Troy Posted 02 February 2008 - 09:50 PM

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You should all be catching the water in your buckets and watering your garden with it, anyway!

*troy hates being in a drought-restricted area...
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### #18 Tal Posted 03 February 2008 - 10:43 AM

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Thanks for the explanation Ron Water goes clockwise here anyway

I wonder what direction water would drain if it's placed in a

a large, circular, symmetrical container (ideally over 1m in diameter and conical), still water (whose motion is so little that over the course of a day, displacements are small compared to the size of the container) escaping through a very small hole

Right on the equator
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### #19 Troy Posted 03 February 2008 - 03:59 PM

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Maybe it would just sit there and not go down the drain at all?
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### #20 zorba the geek Posted 03 February 2008 - 04:09 PM

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Maybe it would just sit there and not go down the drain at all?

Good point there Troy

Btw:We are just waisting water
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### #21 cokane Posted 27 February 2008 - 09:55 AM

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i got 18 of them. the way the ask questions are tricky. had to read some more than once.
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### #22 mrsleadfoot Posted 31 March 2008 - 01:15 PM

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I got 15 out of 25 right. I should know better with some of the questions I got wrong.
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### #23 Artellos Posted 02 April 2008 - 04:30 AM

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15 Questions here.
Some where hard and guess works since some involved US stuff and I live in Holland

Regards,
Olrik
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### #24 Mr. Green Posted 02 April 2008 - 11:05 AM

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HHmmm only 19. Well I guess it really is time to start hitting the books again.
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HydraZulu

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18
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### #26 Nerdlinger Posted 28 April 2008 - 06:44 PM

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19 out of 25. Woot!
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### #27 Connor D Posted 16 May 2008 - 04:04 PM

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18 - And I'm not american

The flag one seemed obvious,
I got the statue of liberty one wrong

And I saw the brainiac with the plugholes

Connor
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### #28 PILL5B3RRY Posted 18 May 2008 - 12:26 AM

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I got 14 out of 25. Its those questions you got to think about... hard!
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Breaku

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19 of 25 here.
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### #30 dsenette Posted 19 May 2008 - 02:50 PM

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*Cough*25*Cough*....take that
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