New concept of 'granular temperature' could shed light on avalanche movement

Brussels, 31 Jan 2005

Scientists in France, Italy and Switzerland have discovered a new concept of temperature which could help to explain how ice and snow particles flow the way they do during an avalanche, and which may also lead to improvements in handling tablets in the pharmaceutical industry.

Granular materials, from sand to snow to powdered sugar, often display strange properties that can make them behave like solids, liquids or even gases, As reported in the current issue of the New Journal of Physics, a team of four researchers have now revealed how to measure something called 'granular temperature' in such materials.

'Take the solid snow covering a ski slope, for instance,' says lead author Patrick Mayor from the Ecole Polytechnique Fédérale de Lausanne (EPFL) in 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.'

Mr Mayor continues: '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. The diverse behaviour of granular materials makes it extremely difficult to establish a general theory that accounts for the observed phenomena.'

The temperature of an object reflects the motion of its constituent parts. For example, the faster the molecules in a gas are moving, the higher the temperature of the gas itself.

Mr Mayor and his colleagues have come up with a thermometer that can measure the temperature of a granular material based on the amount of movement of its constituent parts. Unlike liquids, the temperature of granular material varies depending on how far the thermometer is inserted into the material, they discovered.

Being able to take such measurements could provide researchers with a better understanding of the properties of granular material, knowledge that could be of use to all industries that handle powdered and particulate material, such as the pharmaceuticals and construction industries.

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