A simple method is described to measure the coefficient of rolling friction, ##IMG##
[http://ej.iop.org/images/0143-0807/36/6/065018/ejp519061ieqn3.gif] {${mu }_{{rm{r}}}$} , for a
hard ball rolling on a hard, horizontal surface. The method involves attaching a small mass to the
side of the ball so that the ball precesses slowly along a spiral path. Since the radius of
curvature decreases slowly with time, the decrease in ball speed can be measured over a relatively
long path length on a small area surface. Results are presented for three steel bearing balls and a
billiard ball rolling on a polished granite surface, with ##IMG##
[http://ej.iop.org/images/0143-0807/36/6/065018/ejp519061ieqn4.gif] {${mu }_{{rm{r}}}$} ranging
from 0.000 086 to 0.000 84. Estimates of the combined deformation of the ball and the surface are
also presented, based on impact duration measurements at very low impact forces.