  We show that two basic mechanical processes, the collision of particles and
rolling motion of a sphere on a plane, are intimately related. According to our
recent findings, the restitution coefficient for colliding spherical particles
\epsilon, which characterizes the energy loss upon collision, is directly
related to the rolling friction coefficient \mu_{roll} for a viscous sphere on
a hard plane. We quantify both coefficients in terms of material constants
which allow to determine either of them provided the other is known. This
relation between the coefficients may give rise to a novel experimental
technique to determine alternatively the coefficient of restitution or the
coefficient of rolling friction.
