Billiard ball
A hard, polished sphere struck with a cue or another ball in cue sports. Its material, mass, diameter, and markings vary by game and ball type.
Cue sports: A family of games in which players use cues to strike balls on a table. Billiard balls are the shared playing objects across this family of games.
Elastic collision: A collision in which total kinetic energy is conserved. Billiard-ball impacts approximate elastic collisions, transferring momentum between balls.
Ivory trade: The commerce in elephant tusks and other ivory sources. Ivory became a prominent billiard-ball material, linking the game to wildlife exploitation.
Pool: A cue sport usually played on a pocketed table with numbered object balls. Pool's ball sets include distinctive stripes, solids, and game-specific colors.
Cue ball: The ball a player strikes directly with a cue to contact other balls. Its motion and position determine each shot in pool, snooker, and carom games.
Coefficient of restitution: A measure of how much relative speed two objects retain after colliding. It quantifies how lively or dead a ball-to-ball impact feels.
John Wesley Hyatt: An American inventor associated with the development of celluloid and early plastic manufacturing. His celluloid work offered an alternative to scarce ivory for billiard balls.
Snooker: A cue sport played with 15 red balls, six colored balls, and a cue ball. Snooker assigns different point values to balls distinguished by color.
Object ball: A ball targeted by the cue ball in a cue sport. Its color, number, and role depend on the game being played.
Friction: The resistance to relative motion between surfaces in contact. Friction between ball, cloth, and cushion affects roll, spin, and rebound.