Golf ball

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A golf ball on a tee with a driver ready for a drive

A golf ball is a ball designed for use in the game of golf.

An appendix to the Rules of Golf defines, by the rules of the game, 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).

1 Aerodynamics
2 Design
- 2.1 Examples
3 Selection
4 See also
5 External links
- 5.1 History
6 Footnotes

[edit] Aerodynamics

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 designed 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.

Dimpled balls fly farther than non dimpled balls due to the combination of two effects:

Firstly, the dimples delay separation of the boundary layer from the ball. Early separation, as seen on a smooth sphere, causes significant wake turbulence, the principal cause of drag. The separation delay caused by the dimples therefore reduces this wake turbulence, and hence the drag.

Secondly, backspin generates lift by deforming the airflow around the ball, in a similar manner 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. Unfortunately the dimples magnify this effect as well as the more desirable upward lift derived from pure backspin. (Some dimple designs are claimed to reduce sidespin effects.)

In order to keep the aerodynamics optimal, the ball needs to be clean. Golfers can wash their balls manually, but there are also mechanical ball washers available.

[edit] Design

Most golf balls on sale today have about 300 - 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.

[edit] Examples

These two balls are disclosed in U.S. Patent 4,560,168 . As shown in the illustration, these two balls are easily made with a two-piece mold. And since there is no dimple located on any of these dotted great circles (one of them is red), the mold can be two hemispheres.

Golf balls also come in different colors, which helps with finding the ball when lost or in distinguishing your ball from other players' balls. White is the most common color.

[edit] Selection

There is a variety of golf balls in the market, and customers often face a large number of selections, making decisions hard to make. Basically, golf balls are divided into two categories: recreational and advanced balls. Recreational balls are designed more oriented towards the ordinary golfers, who generally have low swing speeds (80mph or lower) and lose golf balls on the course easily. These balls are made of two layers, with the cover firmer than the core. Their low compression and side spin reduction characteristics suit the low swing speeds of average golfers quite well. Furthermore, they generally have lower prices than the advanced balls. Advanced balls are made of multilayers (three or more), with a soft cover and firm core. They induce a greater amount of spin from lofted shots (wedges especially), as well as a sensation of softness in the hands in short-range shots. However, these balls require a much greater swing speed that only the physically strong players could carry out to compress at impact. If the compression of a golf ball does not match a golfer's swing speed, either the lack of compression or over-compression will occur, resulting in loss of distance. There are also many brands and colours to choose from, (Although coloured balls and better brands are more expensive), making your choice harder.