Physics News Update
The American Institute of Physics Bulletin of Physics News
Number 438 (Story #1), July 9, 1999 by Phillip F. Schewe and Ben Stein
CLUSTERING IN GRANULAR GASES Granular materials (e.g., salt, sand, sugar) share properties with solids (they support a load) and liquids (they pour) but have unique properties of their own owing to the complex ways in which thousands to millions of grains collide with each other. To understand better the ways in which grains move and organize themselves, it would be nice if gravitational interactions could be minimized so that only inter-grain and grain-wall interactions were important. For this reason, French researchers (Eric Falcon, Ecole Normale Superieure, 011-33-1-44-323501, eric.falcon@ips.ens.fr) resorted to outer space. They have performed the first experiment with vibrated granular media in a low-gravity environment. On board a sounding rocket, inelastic frictional collisions among the grains themselves and with the container walls were the only interaction mechanisms at work. Once fluidized (agitated) the grains formed a uniform gas. At higher densities, though, the grains formed dense, motionless, 3-dimensional clusters surrounded by low-density regions. (Falcon et al., Physical Review Letters, 12 July 1999.)
