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Q & A: Coriolis myths

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Most recent answer: 10/22/2007
Q:
I know that water will go down a drain opposite ways in the northern and southeren hemisphers but I want to know would this work exactly? If you where just an inch over the equator and then steped an inch to the other side would it work that closly? how about if you where EAXCTLY on the equator? Also what makes water behave this way in opposite hemispheres?
- James
U.S
A:
That stuff about water going down drains opposite ways in the hemispheres is a myth. In practice, tiny irregularities in real drains or little accidental swirling imparted to the water play a much bigger role, evcen when you're far from the equator. The Coriolis forces, which do twist the water different ways north and south of the equator, become important on a very large scale, in driving weather and persistent currents.

The basic idea behind the effect is this. Angular momentum is conserved. We all have some angular momentum due to the Earth's spin. If you were to keep spinning around with the Earth, your angular momentum would decrease as you approached the center of the Earth, just like the angular momentum of a skater would go down as she pulled her arms in- if her spinning rate didn't change. The angular moment that would be lost as something fell partly goes into a spinning motion of the thing falling.

That's the effect- but like I said it's small for smallish objects.

Mike W.

(published on 10/22/2007)

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