Ball

A ball is a round object that is typically used in games, sports, and play. In common usage, a ball is either hollow or solid and can be inflated. In geometry, however, the term ball has a precise meaning: a solid ball consists of all points within a given distance (radius) of a center, while a sphere refers to the surface at that distance.

Manufacture and material vary widely. Balls may have a core of rubber, plastic, or foam, enclosed by a leather or synthetic cover, and many include an internal air bladder to maintain shape and pressure. The size, weight, and bounce are chosen for the intended sport or activity, and inflation pressure and material elasticity influence performance.

Sports and games rely on balls. Soccer balls are typically size 5, circumference 68–70 cm, and weight 410–450 g. Basketballs are around 75 cm in circumference and 600–650 g in weight. Tennis balls have a circumference about 20–22 cm. Baseballs weigh about 142–149 g. Golf balls are small and hard, about 4.27 cm in diameter. Some sports use non-spherical balls; American footballs and rugby balls are prolate spheroids, not true balls.

History and regulation: Balls have ancient origins and were made from varied materials such as stone, wood, or leather stuffed with air. The development of vulcanized rubber in the 19th century enabled modern inflatable balls, and contemporary standards are set by governing bodies to ensure consistent size and performance across regions and sports.