Foerster et al. [Phys. Fluids 6, 1108 (1994)] proposed a binary collision model for spheres and a way to measure the constant impact parameters in the model. These three parameters were necessary to describe the translational momentum exchange during a collision. An extensive data set for a variety of materials was made possible using these measurements. In recent years many studies have shown that rolling friction between particles has strong effects on the bulk behavior of granular materials. In the present paper, an expansion of the previous collision model is studied to include rolling friction. It is shown that rolling friction does not affect the postcollision linear relative velocities for the conditions used in the impact experiments. Furthermore, it is suggested that the same impact experiment could potentially be used to measure the coefficient of rolling friction.
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