Why does the sugar move towards the centre of the cup when you stir it

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Why does the sugar move towards the centre of the cup when you stir it

[From: ] [author: ] [Date: 11-09-16] [Hit: ]

but it is the same theme.Heres a link to Wikipediahttp://en.wikipedia.org/wiki/Tea_leaf_pa…There is indeed an Ekman layer involved.......

This is consistent with the above explanation.

Now if we took lighter particles. Perhaps sawdust? Then we should not only see them move to the middle but from there we should be able to see them rise and form currents similar to convection currents.

I am going to test this. I have pondered this problem before but never taken the time to truly understand it.

Fascinating.

Of course there are other ideas to test but I don't think they are right.
If heavy things move to the middle for other reasons than the above description then things lighter than the water should move to the outside. But I don't think that this happens.

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Ekman pumping

As spinning fluid spins down in the cup under the action of viscosity, boundary layers are formed at the bottom and sidewalls of the cup. One of the net results of a boundary layer is that slow moving fluid within the layer is pumped out into the faster moving fluid outside the layer (effectively growing the thickness of the layer of slower moving fluid.)

The net circulation pattern that results from the Ekman pumping is for the fluid at the bottom of the cup to move towards the axis of rotation and then be pumped vertically up the axis of symmetry.

Any particles entrained in this circulation pattern (like tea leaves or sugar) will move towards the center of the cup and form a little pile there.

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First you look the Cup, you will see that when you stir the sugar, sugar move towards outside until the centrifugal force decrease. When we stop stirring, the centrifugal force decreases and the sugar comes toward centre.

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Einstein trumps!

It turns out that Einstein did a paper on this in 1926. Well, not on sugar, but tea leaves, but it is the same theme.

Here's a link to Wikipedia

http://en.wikipedia.org/wiki/Tea_leaf_pa…

There is indeed an Ekman layer involved.

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