ضمن تشکر از اظهار نظر صورت گرفته ، محتوای لینک مورد نظر دوستمان در زیر آمده است.
The water in a sink (or toilet) rotates one way as it drains in the
northern hemisphere and the other way in the southern hemisphere.
Called the Coriolis Effect, it is caused by the rotation of the Earth.
First on this page is a discussion of the issue. Towards the bottom of the page you can see examples of incompetence from PBS,NPR, and Sports Illustrated.
The Coriolis force does influence long-lasting vortices.
On the scale of hurricanes and large mid-latitude storms, the Coriolis force causes the air to rotate around a low pressure center in a cyclonic direction. Indeed, the term cyclonic not only means that the fluid (air or water) rotates in the same direction as the underlying Earth, but also that the rotation of the fluid is due to the rotation of the Earth. Thus, the air flowing around a hurricane spins counter-clockwise in the northern hemisphere, and clockwise in the southern hemisphere (as does the Earth, itself). In both hemispheres, this rotation is deemed cyclonic. If the Earth did not rotate, the air would flow directly in towards the low pressure center, but on a spinning Earth, the Coriolis force causes that air to be deviated with the result that it travels around the low pressure center.
In the accompanying picture of the Caribbean, one can see the cyclonically spiraling clouds of Hurricane Andrew (at the mouth of the Mississippi) and of another vortex in the Atlantic.
But, the Coriolis force is very small, indeed.
Compared to the rotations that one usually sees (tires on a travelling automobile, a compact disc playing music, or a draining sink), the rotation of the Earth is very small: only one rotation per day. The water in a sink might make a rotation in a few seconds and so have a rotation rate ten thousand times higher than that of the Earth. It should not be surprising, therefore, to learn that the Coriolis force is orders of magnitude smaller than any of the forces involved in these everyday spinning things. The Coriolis force is so small, that it plays no role in determining the direction of rotation of a draining sink anymore than it does the direction of a spinning CD.
The direction of rotation of a draining sink is determined by the way it was filled, or by vortices introduced while washing. The magnitude of these rotations may be small, but they are nevertheless gargantuan by comparison to the rotation of the Earth. I decided to include a picture of a draining sink, and the first one I tried in my house was found to drain clockwise (the opposite of what the silly assertions would have it do here in the northern hemisphere). This direction was determined entirely by the way the tap filled the sink. The direction of rotation of a draining toilet is determined by the way the water just under the rim is squirted into the bowl when it is flushed.
Is it possible to detect the Earth’s rotation in a draining sink?
Yes, but it is very difficult. Because the Coriolis force is so small, one must go to extraordinary lengths to detect it. But, it has been done. You cannot use an ordinary sink for it lacks the requisite circular symmetry: its oval shape and off-center drain render any results suspect. Those who have succeeded used a smooth pan of about one meter in diameter with a very small hole in the center. A stopper (which could be removed from below so as to not introduce any spurious motion) blocked the hole while the pan was being filled with water. The water was then allowed to sit undisturbed for perhaps a week to let all of the motion die out which was introduced during filling. Then, the stopper was removed (from below). Because the hole was very small, the pan drained slowly indeed. This was necessary, because it takes hours before the tiny Coriolis force could develop sufficient deviation in the draining water for it to produce a circular flow. With these procedures, it was found that the rotation was always cyclonic.
Why do teachers claim that a draining sink reflects the rotation of the Earth?
A surprisingly large number of my undergraduate students tell me that their high-school teachers told them that sinks drain in opposite directions in the two hemispheres owing to the rotation of the Earth. Why would a teacher offer such garbage to students when it is so easy to check. A trip to the school washroom (let alone the ones at home) will reveal drainage in both directions (which would certainly require the equator to assume a tortuous track through the countryside).
Is knowledge just a bunch of abstractions to be memorized with no recourse to the relevance of everyday experience?
Sigh... I don’t know why teachers do this. I can but assume that those who do so just never feel any need to wash their hands --- or their minds.