Granular physics: creating a dry variety of quicksand.
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.
Lohse
Detlef
D
Faculty of Science and J.M. Burgers Centre for Fluid Dynamics, University of Twente, 7500 AE Enschede, The Netherlands. d.lohse@utwente.nl
Rauhé
Remco
R
Bergmann
Raymond
R
van der Meer
Devaraj
D