An appendix to the "Rules of Golf" defines that a golf ball must not weigh more than 45.93 grams (1.620 oz), that its diameter must not be less than 42.67 mm (1.680 in), and that its shape may not differ significantly from a symmetric sphere. Like golf clubs, golf balls are subject to testing and approval by the Royal and Ancient Golf Club of St Andrews and the United States Golf Association, and those that do not conform with the regulations may not be used in competitions (Rule 5-1).
Wooden balls were used until the early 17th century, when the featherie ball was invented. A featherie is a handsewn cowhide bag stuffed with goose feathers and coated with paint. Due to its superior flight characteristics, the featherie remained the standard ball for more than two centuries.
In 1848, the Rev. Dr. Robert Adams (or Robert Adam Paterson) invented the gutta percha ball (or guttie). Because gutties were cheaper to produce and could be manufactured with textured surfaces to improve their aerodynamic qualities, they replaced feather balls completely within a few years.
In the twentieth century, multi-layer balls were developed, first as wound balls consisting of a solid or liquid-filled core wound with a layer of rubber thread and a thin outer shell. This design allowed manufacturers to fine-tune the length, spin and "feel" characteristics of balls. Wound balls were especially valued for their soft feel.
Today's golf balls have progressed into having cores of titanium compounds, hybrid materials, softer shells and a more pressurized core. They usually consist of a two-, three-, or four-layer design, consisting of various synthetic materials like surlyn or urethane blends. They are available in a great variety of playing characteristics to suit the needs of golfers of different proficiency.
When a golf ball is hit, the impact, which lasts less than a millisecond, determines the ball’s velocity, launch angle and spin rate, all of which influence its trajectory (and its behavior when it hits the ground).
A ball moving through air experiences two major aerodynamic forces: lift and drag. Drag slows the forward motion, whereas lift acts in a direction perpendicular to it. The magnitude of these forces depends on the behavior of the boundary layer of air moving with the ball surface.
Every modern golf ball has dimples; their purpose is to increase and shape the lift and drag forces by modifying the behavior of the boundary layer. It should be noted that drag and lift forces exist also on smooth balls: they are only modified, not created, by dimples.
One effect of dimples is a reduction of drag, contributing to the increased length of flight of dimpled balls compared with smooth ones.
A spinning ball deforms the flow of air around it, creating lift in a way similar to an airplane wing. Backspin is imparted in almost every shot due to the golf club's loft (i.e. angle between the clubface and a vertical plane). A backspinning ball experiences an upward lift force which makes it fly higher and longer than a ball without spin would. Sidespin occurs when the clubface is not aligned perpendicularly to the direction of swing, leading to a lift force that makes the ball curve to one side or the other. These lift forces may be further increased through the presence of dimples. (Some dimple designs are claimed to reduce sidespin.)
In order to keep the aerodynamics optimal, the ball needs to be clean. Golfers can wash their golf balls manually, but there are also mechanical ball washers available.
Most balls on sale today have about 300 to 450 dimples. There were a few balls having over 500 dimples before. The record holder was a ball with 1,070 dimples -- 414 larger ones (in four different sizes) and 656 pinhead-sized ones. All brands of balls, except one, have even-numbered dimples. The only odd-numbered ball on market is a ball with 333 dimples.
Officially sanctioned balls are designed to be as symmetrical as possible. This symmetry is the result of a dispute that stemmed from the Polara, a ball sold in the late 1970s that had six rows of normal dimples on its equator but very shallow dimples elsewhere. This asymmetrical design helped the ball self-adjust its spin-axis during the flight. The USGA refused to sanction it for tournament play and, in 1981, changed the rules to ban aerodynamic asymmetrical balls. Polara's producer sued the USGA and the association paid US$1.375 million in a 1985 out-of-court settlement.
The United States Patent and Trademark Office's patent database is a good source of past dimple designs. Most designs are based on Platonic solids such as icosahedron.