Granular physics: creating a dry variety of quicksand.

Lohse, Detlef; Rauhé, Remco; Bergmann, Raymond; van der Meer, Devaraj · Nature · 2004

basic_science · Level V

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Abstract

Sand can normally support a weight by relying on internal force chains. Here we weaken this force-chain structure in very fine sand by allowing air to flow through it: we find that the sand can then no longer support weight, even when the air is turned off and the bed has settled--a ball sinks into the sand to a depth of about five diameters. The final depth of the ball scales linearly with its mass and, above a threshold mass, a jet is formed that shoots sand violently into the air.