Physics of sports; trajectories dense particles; High Reynolds number
Abstract :
[en] This experimental work deals with sports balls trajectories. Those dense projectiles are laun- ched in air at several hundred kilometers per hour. In this situation, ball trajectories depend on the fluid flow around them which occurs at high Reynolds number (Re > 1000). The first effect we consider is the fluid drag. This friction reduces the range and gives rise to trajectories very different from parabola which are non symmetric toward the top. This kind of trajectories occurs in badminton for high clears. Nicollo Tartaglia was the first to draw those curves observing the trajectories of cannon balls. However, the air doesn’t only limit the forward motion. When balls spin, the Robin-Magnus effect produces a lateral force and curves the trajectory. This is studied in the case of clearances in soccer. Lateral aerodynamic forces also exist when the ball has no spin. The turbulent behavior of the flow around a spherical particle provides lateral forces with complex temporal dependency. This induces zigzag trajectories which are occasionally observed in volley, soccer and baseball. We inspect the condition of occurrence of this phenomenon. Then, the case of non spherical balls are considered. Such balls are used in rugby, football and badminton. Shuttlecocks have the propriety to fly the nose ahead which oblige them to flip after each racket impact. Finally, we study the motion of a fluid particle with the particular case of a Leidenfrost liquid ring. A such object is created by approaching an annular magnet from a paramagnetic liquid oxygen drop. The closing dynamics of this non wetting ring is described with by the way of a potential flow approach.
