Force is the key to granular state-shifting

Ever wonder why sand can both run through an hourglass like a liquid and be solid enough to support buildings? It's because granular materials -- like sand or dirt -- can change their behavior, or state. Researchers from North Carolina State University have found that the forces individual grains exert on one another are what most affect that transition.

Fuente : http://www.eurekalert.org/pub_releases/2013-02/ncs...