Motion-induced quicksand
From a mechanical perspective, granular materials are stuck between a rock and a fluid place, with behavior resembling neither a solid nor a liquid. Think of sand through an hourglass: As grains funnel through, they appear to flow like water, but once deposited, they form a relatively stable mound, much like a solid. Ken Kamrin, an assistant professor of mechanical engineering at MIT, studies granular materials, using mathematical models to explain their often-peculiar behavior. Now Kamrin has applied a recent granular model, developed by his group, and shown that it predicts a bizarre phenomenon called “motion-induced quicksand” — a scenario in which the movement of sand in one location changes the character of sand at a distance. “The moment you start moving sand, it acts like fluid far away,” Kamrin says. “So, for example, if you’re walking in the desert and there’s a sand dune landslide far away, you will start to...