Collision between two balls accompanied by deformation: A qualitative approach to Hertz’s theory

When real balls collide they suffer deformation. Though the theory of collision accompanied by elastic deformation has been developed by H. Hertz a long time ago, it is rarely accounted for in elementary courses because of its mathematical intricacies. It is shown that an order-of-magnitude approach is nevertheless possible, and that the essentials of Hertz’s results can be obtained without recourse to complicated calculations.