Bowling balls

A bowling ball is a piece of sporting equipment used to hit bowling pins in the sport of bowling. Ten-pin bowling balls are typically hard spheres with three holes drilled in them, one each for the ring and middle fingers, and one for the thumb. Regulating bodies such as the USBC maintain requirements for the properties of bowling balls, including size, hardness, and number of holes, as well as maintaining a list of bowling balls approved for competitive play. Other bowling balls, such as those used in five-pin bowling, candlepin bowling, and duckpin bowling are smaller, lighter, and without holes, so that they may be held in the palm of the bowler's hand. Most bowling alleys provide balls for patrons to use within the establishment, often referred to as "house balls."

Key properties of ten-pin bowling balls include surface friction, porosity, and mass distribution, which affect the motion of the ball as it rolls. These properties are varied to control how much a ball will slide through the oily surface of a typical bowling lane, and how easily a ball will change direction when the roll is combined with rotational motion. Friction and porosity are variables of the surface of the ball, known as the "cover stock," while mass distribution is determined by the shape and size of the core.

The USBC and FIQ specifies that bowling balls may only be made from uniform, solid materials with a density less than or equal to 3.80 g/mL. The weight of the ball must not exceed 16.00 pounds (7.26 kg), with no lower bound for weight. The hardness of the ball must be at least 72, as measured by a Type D Shore durometer at room temperature (68-78 degrees Fahrenheit). A ball may have a circumference between 26.704 inches (67.83 cm) and 27.002 inches (68.59 cm), and a diameter in the range of 8.500 inches (21.59 cm) to 8.595 inches (21.83 cm).

...
Wikipedia