why in a mixture of different size same density steel balls we have a separation when shaken?
When you open a can of mixed nuts, why are the Brazil nuts on top? The segregation of large and small nuts is called the Brazil Nut Effect. Do a google search on the Brazil Nut Effect.
I searched on "Brazil Nut Effect" in quotes and got 179,000 hits.
For the same reason, farmers keep having to clear their fields of large stones and boulders, which constantly find their way to the surface.
But why does it happening? Even when all the components have the same density it seems that the larger particles falls slower than the small particles...
and nobody can explain the reason why small particles get at the bottom!
Yes they can. If you have a mixture of large and small particles, the small one can fall in between the big ones every time the mixture is shaken, and take small steps toward the bottom. On the other hand, the big one cannot fall through spaces between little ones. It is very hard for the big ones to push small ones up.
The above post says it all.
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