A theory is developed for the reaction of plates to forces of such short duration that the waves reflected from the boundary may be neglected. It is found that the velocity of the point of application of the force is proportional to the force, and hence the total displacement is proportional to the impulse of the force. The theory is applied to the impact of spheres with large plates. The coefficient of restitution is obtained as a function of the parameters of the impact. Complete agreement is obtained with previous experiments.

• Received 21 February 1941

DOI:https://doi.org/10.1103/PhysRev.59.669