Open questions on the impact of an inflated ball

The behaviour of sports balls during impact defines some special features of each sport. The velocity of the game, the accuracy of passes or shots, the control of the ball direction after impact, the risks of injury, are all set by the impact mechanics of the ball. For inflated sports balls, those characteristics are finely tuned by the ball inner pressure. As a consequence, inflation pressures are regulated for sports played with inflated balls. Despite a good understanding of ball elasticity, the source of energy dissipation for inflated balls remains controversial. We first give a clear view of non-dissipative impact mechanics. Second we review, analyse and estimate the different sources of energy dissipation of the multi-physics phenomena that occur during the impact. Finally, we propose several experiments to decide between gas compression, shell visco-elastic dissipation, solid friction, sound emission or shell vibrations as the major source of energy dissipation.