Oblique impact of a buckling table-tennis ball on a rigid surface.

We report on the rebound of a table-tennis ball impinging without any initial spin in oblique incidence on a rigid surface. We show that, below a critical incidence angle, the ball rolls without sliding when bouncing back from the surface. In that case, the reflected angular velocity acquired by the ball can be predicted without any knowledge of the properties of the contact between the ball and the solid surface. Beyond the critical incidence angle, the condition of rolling without sliding is not reached within the time of contact with the surface. In this second case, one can predict the reflected angular and linear velocities, as well as the rebound angle, provided the supplementary knowledge of the friction coefficient associated with the ball-substrate contact.

Dynamical buckling of a table-tennis ball impinging normally on a rigid target: Experimental and numerical studies.

We report on the dynamical buckling of a spherical shell (a table-tennis ball) impinging in normal incidence on a rigid surface (a glass plate). Experimentally, we observe and decipher the geometrical characteristics of the shell profile in the contact region along with global metrics such as the contact duration and the coefficient of restitution of the linear velocity. We determine, in particular, the onset of the ball buckling instability. We find that, just like in quasi-statics, the shell buckles when the crushing exceeds about twice the thickness of the shell. In addition, for launching conditions resulting in the ball elastic buckling, a drop in the restitution coefficient is observed. A companion numerical finite elements study is set to monitor the different sources of energy and reveals that the added energy loss is mainly due to the friction between the shell surface and the solid substrate.