I'd like to know which methods I could use to reduce the loss of kinetic energy when two iron balls collide, or when a plastic ball collides with the floor after a free fall. I have tried to cover the floor with a fabric that would make it more elastic, but it had a small effect (if it hat effect at all). The general case is the loss of a considerable amount of mechanical energy with the "crack" sound between the two surfaces. All the solutions I thought would help reduce the sound energy, but would involve bodies whose internal vibration in the collision (bodies who suffer considerable deformation), and the result is practically the same. My goal is to transfer the maximum of the momentum of m1 to m2, or to make m1, colliding with the floor, to bounce back as high as it can.