The physics of sandpiles

The physics of sandpiles
2/14/08

What is more ordinary than a sand pile? Even watching the sand pile up at the bottom of an hourglass is old hat for most. Still, researchers are drawn to the complex physics that underlies the formation of a sand pile or other piles of various kinds of grains or powders. Physicist Geoffroy Lumay wrote a doctoral dissertation about this matter under the direction of Nicolas Vandewalle.

The physics of granular materials, better known as “sandpile physics”, aims at the characterization of certain aspects of powders, grains, spheres, etc. The GRASP laboratory (Group for Research and Applications in Statistical Physics) at the University of Liege is devoting part of its research effort to this problem. This effort has focused on a very ancient question that arises from everyday life: how much space will a pile of grains (of sand or something else) occupy? The answer to this question applies, obviously, to problems involved in the packaging of products. How many apples will fit into a carton? How much flour can be placed in this bag? How can we optimize the volume of a pile of something? This kind of physics is also the reason for the graduated measuring cups we use in kitchens.

Sandpile physics looks for quantitative answers to such questions that may seem simple at first, since after all things like apples and flour are pretty familiar to us. But the great complexity of these ordinary situations arises when you try to describe them in terms of equations. Many studies dealing with these things begin with a simplification of reality – for example by supposing that all the grains are spherical, or that they pile up in an orderly manner. Without these simplifying hypotheses, though, the problems are real head-breakers…but certain physicists like them that way.

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