Sphere collision response problem

Hi, for sphere collision response i use this code: vec x_axis = p2->pos - p1->pos; x_axis.norm(); vec U1x = x_axis * (x_axis * p1->vel); vec U1y = p1->vel - U1x; vec U2x = x_axis * (x_axis * p2->vel); vec U2y = p2->vel - U2x; vec e1 = U1x * p1->mass; vec e2 = U2x * p2->mass; vec e3 = (U1x - U2x) * p2->mass; vec e4 = (U2x - U1x) * p1->mass; vec e12 = e1 + e2; float odm = 1.0f / (p1->mass + p2->mass); vec V1 = U1y + (e12 - e3) * odm; vec V2 = U2y + (e12 - e4) * odm; p1->vel = V1; p2->vel = V2; it works good, but there is one problem: sometimes when velocity is small first sphere connects to second 1) how to fix this problem? 2) maybe there are faster method to do it?