Ball in order to set of sport, in particular, tennis

摘要

The ball has an inner sphere (2), made of an elastomer material, and an outer reinforcing cover. The cover is a spherical frame made from a wire (12) that is wound round the outer surface of the sphere to enclose it. For each turn of the wire the direction of the wire at two opposite points (14,16) on the sphere are inclined to each other by an angle of 20-90 degrees The distance (d) separating any two points on one turn of the wire is less than the diameter (D) of the sphere, so that successive turns do not converge.