Golf Equipment - The
Golf Ball
An appendix to the "Rules
of Golf" defines that a golf ball must not weigh more 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).
History
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.
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 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.
In order to keep the aerodynamics optimal, the ball needs to be clean.
Golfers can wash their golf balls manually, but there's also mechanical
ball washers available.
Design
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.
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.
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