Violently shaking a box of breakfast cereal does not make the
particles act exactly like molecules in an ideal gas, but there
are similarities. According to the 23 October PRL there is a
simple mathematical expression for the distribution of particle
velocities in a shaken box of steel beads which–like the formula
for gas molecules–depends only on the average speed of the
particles and not on the density or details of the shaking. To
model problems such as grain motion in silos, soil shifting in
earthquakes, and dry foods mixing in processing plants,
physicists studying granular materials want equations as simple
and comprehensive as those for gases and fluid motion. The new
results suggest that such a theory may be possible. The century-
old kinetic theory of gases assumes the gas molecules are in
equilibrium with their surroundings–they exchange energy with
the outside world each time a molecule collides with a wall. But
the particles in a granular material are not in equilibrium;
they constantly soak up ene