Granular liquids with zero surface tension
DOI: 10.1063/1.2835143
New experiments with spherical glass beads show that liquid behavior can arise simply from rapid collisions among a sufficiently dense stream of particles. If one or two beads are dropped onto a horizontal target, they will rebound back the way they came. However, physicists at the University of Chicago have now shown that when many beads are propelled at a target all at once in a dense granular stream, the grains deflect out laterally in the form of a very thin, symmetrical sheet or cone as if they constituted a liquid (see the figure). Indeed, the experiments using noncohesive granular particles quantitatively reproduce results obtained with streams of water in the limit of vanishing surface tension. To ensure there was no cohesion between the beads, the researchers baked them in a vacuum oven to evaporate any lurking moisture. The stream’s liquidlike conditions are established near the target in a small region where the incoming and rebounding beads rapidly collide with each other. As the density of the stream decreases, the particulate nature of the flow gradually reasserts itself. (
