Terminal velocity of a heavy object in a superlight granular medium
CIMAV, Monterrey, Mexico
Vendredi 24/09/2010, 11:00
NIMBE Bât 125, p.157, CEA-Saclay

A granular material is a system composed of many solid particles interacting mainly

through contact forces. Therefore, the dissipation of energy usually plays a dominant role

in the dynamics of these materials. For this reason, in experiments done so far, when an

object impacts on a granular bed it eventually dissipates all its energy and comes to rest.

In contrast, when a dense enough object is placed inside a fluid it keeps falling,

asymptotically approaching a terminal velocity.

Here we present experiments of a heavy object falling into a silo full of expanded

polystyrene spherical particles. The density of the granular medium is so low that it can not

bear the weight of an intruder whose mass is beyond a threshold value, even if the object

is very deep in the silo. We systematically vary the mass of an object impacting in such a

granular bed and we find a transition between the commonly observed behavior where the

object stops at a given depth, and a situation where the object keeps falling and reaches a

terminal velocity, just as in a fluid.

Contact : Florent MALLOGGI


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