page_title: Bouncing ball
section_title: Non-spherical balls
hierarchical_section_title: Bouncing ball / Impact / Non-spherical balls
context_page_description: The physics of a bouncing ball concerns the physical behaviour of bouncing balls, particularly its motion before, during, and after impact against the surface of another body. Several aspects of a bouncing ball's behaviour serve as an introduction to mechanics in high school or undergraduate level physics courses. However, the exact modelling of the behaviour is complex and of interest in sports engineering.
  The motion of a ball is generally described by projectile motion, while its impact is usually characterized through the coefficient of restitution. To ensure fair play, many sports governing bodies set limits on the bounciness of their ball and forbid tampering with the ball's aerodynamic properties. The bounciness of balls has been a feature of sports as ancient as the Mesoamerican ballgame.
context_section_description: The bounce of an oval-shaped ball (such as those used in gridiron football or rugby football) is in general much less predictable than the bounce of a spherical ball. Depending on the ball's alignment at impact, the normal force can act ahead or behind the centre of mass of the ball, and friction from the ground will depend on the alignment of the ball, as well as its rotation, spin, and impact velocity. Where the forces act with respect to the centre of mass of the ball changes as the ball rolls on the ground, and all forces can exert a torque on the ball, including the normal force and the force of gravity. This can cause the ball to bounce forward, bounce back, or sideways. Because it is possible to transfer some rotational kinetic energy into translational kinetic energy, it is even possible for the COR to be greater than 1, or for the forward velocity of the ball to increase upon impact.
caption: The forces acting on a gridiron football ball or rugby ball at impact are the force of gravity, the normal force, and the force of friction. Friction will normally have a 'longitudinal' component due to the ball's velocity and 'tumbling' spin and a 'sideways' component due to the 'on-axis' spin of the ball induced by the throw.