We consider grains with rotational degrees of freedom, experiencing frictional forces when colliding. We show that the rotational motion of a grain is correlated with its linear velocity. A simple theory is derived for these correlations. We furthermore compute the distribution for the partitioning of energy into rotational and translational degrees of freedom, $x=E_{rot}/E_{trans}$. This distribution is nontrivial due to the breakdown of equipatition and even singular.

Université de Goettingen