Contact of Viscoelastic Spheres

are the effective radius and mass of thegrains, respectively. A is a material constant depending on the Young modulus, theviscous constants and the Poisson ratio of the material. The initial conditions forsolving (2) are ξ(0) = 0 and ξ˙(0) = g. The coefficient of restitution ǫ of at timet = 0 colliding spherical grains can be found from this equation relating the relativenormal velocities g = ξ˙(0) at time of impact and at time t