Computers are ideal for solving such problems, but there's a snag: There are enough interactions in a single
bag of coffee to overwhelm a supercomputer. When scientists and engineers need to deal with
granular materials like soils and powders, they usually approach the problem empirically - that is, they measure how the material behaves in real life and make predictions accordingly. But the empirical approach is limited to things easily measured. Some things aren't. For example, what triggers avalanches on the Moon? How much soil can flow down a chute on Mars? Or, right here on Earth, what happens to damp sand underneath a building during an earthquake? To answer such questions we need a theory, a PV=nRT for granular flows, that can make predictions under a wide range of circumstances. NASA-supported researchers are working to develop such a theory through a combination of experimentation and mathematics. Jenkins, for example, is studying differential equations that describe molecular gases. It might be possible, he says, to adapt them for granular flows. He plans to test some of his ideas using a rotating chamber filled with beads; the device is slated for launch to the International Space Station (ISS) in 2007.We do this on the ISS, he
explains, because granular flows are affected by both gravity and internal collisions. We need to get Earth's gravity out of the picture to create a simpler system. For the same reason, engineering professor Stein Sture of the University of Colorado is leading a series of experiments called Mechanics of Granular Materials (MGM) onboard the space shuttle. His device repeatedly squeezes a column of damp sand and records what happens. The goal, explains Sture, is to understand the liquid-like behaviour. of soil during some earthquakes. MGM has flown before on shuttle missions STS-79 and STS-89, and it's slated for another flight in 2003 onboard the shuttle Columbia (STS-107). Earthquakes, avalanches, planetary rings, coal mines ... even bags of coffee. From the alien to the ordinary, we'll understand them all a little better when this research is done.