Golf Article - The Aerodynamics Of The Golf Ball
Every wonder why a golf ball has dimples? It's not a question that comes up a lot during golf lessons or group golf instructions sessions. But every once in a while, someone will ask about dimples. Some golfers think they're just for decoration. Well, they're not. There's a practical reason why golf balls have dimples. It has to do with the aerodynamics of drag.
Evolution of Ball Designs
Put simply, the dimples add spin to the ball, which helps it go farther. Thus, the length of your shot isn't solely dependent on the golfer's strength and mechanics. Dimples also provide control. They enable golfers to hit draws and fades and stop balls dead on the green. If golfers couldn't do this, they'd have to take a lot more golf lessons to achieve a low golf handicap.
The golf ball's design has evolved over the years. At first, golfers used the "featherie”
a leather pouch filled with goose feathers. Then in the 1840s, they switched to a ball, made from the gum of the Malaysian Sapodilla tree. Both balls had smooth surfaces because golfers believed a smooth sphere resulted in less drag. Less drag meant longer shots.
But according to golf legend a professor at Saint Andrews University in Scotland discovered that a sphere goes farther when scored. This discovery led to a variety of golf ball surface designs chosen more or less by intuition. Eventually, golf settled on dimples because of its beneficial effects on drag. Today, the modern golf ball has well over 300 dimples arranged in rows.
Drag On A Sphere
A sphere experiences two types of drag. The first is drag due to friction. This only accounts for a small part of the drag experience, however. The drag due to separation of flow behind the ball, known as pressure, provides the majority of drag on your ball. With laminar flow, separation is early. With turbulent flow, separation is delayed.
The separation region with turbulent flow is smaller than with laminar flow. The smaller separation results in less pressure on the sphere. The scoring causes the flow to change from laminar to turbulent. The turbulent flow has more energy than the laminar flow, so the flow stays attached longer, causing the ball to go farther. Obviously, hitting the ball farther can help your golf handicap.
Achieving The Same Affect
Dimples use another method to impact drag. Physics measures this effect using something called a Reynolds number. It indicates when the flow transitions from a laminar to a turbulent state. As the Reynolds number increases, the ball's drag increases. The average Reynolds number for a smooth sphere is much larger than the average Reynolds number experienced by a golf ball. In other words, the dimples cause the flow to remain longer on a golf ball, propelling it farther.
Lift is another aerodynamic force impacting the ball's flight. Given the proper spin, a golf ball produces lift. Dimples also help generate lift. By keeping the flow attached, the dimples help promote the change in flow described above. If the ball is moving from left to right, the ball is spinning in the counter clockwise direction. The wake is then being deflected downward. This downward deflection of flow results in a lifting force being applied to the ball.
What does this mean for a golfer? Dimples increase the golfer's ability to control the ball and make it do what he or she wants. In one of our golf tips newsletter we explain how to hit a draw. Dimples encourage the drawing action. Without them, it would be extremely difficult to make the ball curve the way you want it to, no matter how much you practiced or how many golf lessons you took. Thus, your golf handicap could suffer.
So when someone asks why a golf ball has dimples, you'll have the answer. They provide better control and help add length to a shot.
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