Everything from powdery snow to desert sands, from salt to corn flakes are granular materials. Physicists have known for many years that granular materials have many perplexing properties that make them behave at times liquid solids, liquids, and even gases. This new research reveals for the first time how to measure a concept called "granular temperature" that could be the key to explaining how they behave.
"Take the solid snow covering a ski slope, for instance", suggests lead author of the paper Patrick Mayor of the EPFL in Lausanne, Switzerland. "While it stays still it is a solid, but as soon as it starts flowing downhill as happens during an avalanche the flowing material is behaving more like a liquid. Similarly, during a desert storm, sand grains are whipped up and behave like molecules in a gas, rather than as a solid".
"Whereas most materials are usually described as solid, liquid or gases, granular systems do not seem to fall into any of these categories and are often considered a separate state of matter of their own," says Mayor, "The diverse behaviour of granular materials makes it extremely difficult to establish a general theory that accounts for the observed phenomena."
Mayor and his colleagues, Gianfranco D'Anna, Alain Barrat, Vittorio Loreto, have shown that shaken granular matter behaves in a way related to Einstein's theory of Brownian motion, first published in 1905.
Contact: David Reid
Institute of Physics