Hi! I am having a little trouble with a question asked by a colleague. There’s a ball B with a certain mass M, at rest. A small ball A of mass m is moving with speed v toward M. If m=M, and the collision is perfectly elastic and the two objects perfectly rigid, than we know that A would come at rest and B will start to move with velocity V. Now if M = 2m, than upon collision, A would rebound with a velocity V1 and B would start to move with a velocity V2. These are one-dimensional collisions. If I have to think about the forces that B exerts on A during the collision in the two cases above, than: If the collisions are instantaneous, impulse imparted to A in second case is greater than in first. That means, when B has a greater mass, it offer greater inertial resistance. Is it right to say that the contact force from B in the second case is greater? Since normal force has its roots in electromagnetic forces, is it okay to say that now that the mass has increased, the normal force is greater? How else would I quantify that inertial resistance? Does an increase in mass leads to an increase in rigidity?