Large sphere surrounded by small spheres rises to surface

a href ="http://berkeleyphysicsdemos.net/taxonomy/term/4">(C)Properties of Heat and Matter - C+25: Fluid Dynamics

Here a large steel ball is submerged underneath a lot of small steel balls and the system is shook. The large steel ball rises to the surface and then remains there as the system is shook more. This is one of the ways buried large stones can rise to the surface of the ground over time.
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C+25+82
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