In addition, F exerts a torque on the ball that changes its rotationspeed. There is a vertical force N, called the normal reactionforce, which acts to change the vertical speed of the ball, and there is ahorizontal friction force, F, that acts to change the horizontal speed of theball. The problem is more complicatedthan one might expect. If a ball is incident at a certain speed andangle on a surface, then how fast does it bounce, at what angle, and with howmuch spin? The followingdiagram illustrates the problem. There is a lot of interesting physics in both of theseevents.Ī fundamental physics problem inball sports is to measure or calculate the way the ball bounces.
The ballgrips the table during each bounce and reverses both its direction of motionand the spin direction. The ball retracesits incident path when it bounces on the right hand side of the table. The two dashed lineson the board are 100 mm apart.Ĭlick the photo to see a fascinating series of bounces of aspinning superball, filmed in slow motion. It then grips the board and rolls over the chalk.
The ball slides at the start of the bounce and sweeps away thechalk. The photo above shows thefootprint of a high speed rubber ball incident from the left on chalk on ablackboard. Rod Cross, Physics Dept, Sydney University Updated June 2014
