Baptiste Darbois Texier, Caroline Cohen, David Quéré and Christophe Clanet

New Journal of Physics 18, July 2016

Zigzag paths in sports ball trajectories are exceptional events. They have been reported in baseball, volleyball and soccer. Such trajectories are associated with intermittent breaking of the lateral symmetry in the surrounding flow. The different scenarios proposed in the literature (such as the effect of seams in baseball) are first discussed and compared to existing data. Then experiments are performed on zigzag trajectories and a new explanation is proposed based on unsteady lift forces. In a second step, ind tunnel measurements of these unsteady lift forces are exploited to solve the equations of motion for various sports and deduce the characteristics of the zigzags, pointing out the role of the drag crisis. Finally, the conditions for the observation of such trajectories in sports are discussed.