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Ne morate, kao Bart Simpson, zvati tetku u Australiji, evo zanimljivog sajta na dilemu strana na koje se vrti voda u slivniku na suprotnim zemljinim poluloptama, zasto mislimo da su te strane suprotne,a zasto one to ipak nisu!
Which Way Will my Bathtub Drain?
Question: Does my bathtub drain differently depending on whether I live in the northern or southern hemisphere?
Answer: No. There is a real effect, but it is far too small to be relevant when you pull the plug in your bathtub.
Because the earth rotates, a fluid that flows along the earth's surface feels a "Coriolis" acceleration perpendicular to its velocity. In the northern hemisphere, Coriolis acceleration makes low pressure storm systems spin counterclockwise; however, in the southern hemisphere, they spin clockwise because the direction of the Coriolis acceleration is reversed. This large-scale meteorological effect leads to the speculation that the small-scale bathtub vortex that you see when you pull the plug from the drain spins one way in the northern hemisphere and the other way in the southern hemisphere.
But this effect is VERY weak for bathtub-scale fluid motions. The order of magnitude of the Coriolis acceleration can be estimated from size of the "Rossby number" (1) (see below). The effect of the Coriolis acceleration on your bathtub vortex is SMALL. To detect its effect on your bathtub, you would have to get out and wait until the motion in the water is far less than one rotation per day. This would require removing thermal currents, vibration, and any other sources of noise. Under such conditions, never occurring in the typical home, you WOULD see an effect. To see what trouble it takes to actually see the effect, see the reference below. Experiments have been done in both the northern and southern hemispheres to verify that under carefully controlled conditions, bathtubs drain in opposite directions due to the Coriolis acceleration from the Earth's rotation (2).
http://math.ucr.edu/home/baez/physics/General/bathtub.html
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