Science Fair Project Encyclopedia
An appendix to the "Rules of Golf" defines that a golf ball must not weigh less than 45.93 grams, that its diameter must not be less than 42.67 mm, 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 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 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 microsecond, determines the ballís 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 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, thus acting 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 a side. These lift forces are further increased through the presence of dimples.
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. There was a ball that had six rows of normal dimples on its equator, and very shallow dimples elsewhere. This asymmetrical design helps the ball self-adjust its spin-axis during the flight. The USGA did not sanction it and changed the rules to ban aerodynamic asymmetrical balls. The ball supplier sued the USGA and the USGA paid US$1.375 million in an out of court settlement.
These two balls are disclosed in U.S. patent No. 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 Ball Dimples - How Many? (written for kids)
- Golf ball aerodynamics
- Flight Dynamics of Golf Balls
- Aerospace Grad Making His Mark on the Game of Golf
- Sci. Am.: How do dimples in golf balls affect their flight?
- Making a Dent: Dimple technology continues to aid advancements in golf balls
- Principles of Aerodynamics
- Evolution of the Dimpled Golf Ball
- Let's See How It'll Fly
- On Golf Ball Design (DOC format)
- A St. Mary's Project: The Aerodynamics of Golf Ball Flight (PDF format)
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