Why Golf Balls Have Dimples

USGA engineer Steve Quintavalla explains why a golf ball is designed with tiny dimples, or impressions, on its surface. "Science of Golf" is produced in partnership with the United States Golf Association and Chevron.

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DAN HICKS reporting: It's one of the most recognizable designs in all of sports.

STEVE QUINTAVALLA (Equipment Standards, USGA): It's a small sphere, it's about 1.68 inches or larger, and it has a lot of valleys or dimples in the surface.

HICKS: What makes the golf ball so unique is not just its small shape, but hundreds of small impressions, or dimples, on its surface. Steve Quintavalla is an engineer in the Equipment Standards Department at the United States Golf Association. He says dimples are crucial to a golf ball's flight.

QUINTAVALLA: A golf ball has dimples to reduce wind resistance or aerodynamic drag. When you reduce it, you can make golf balls go a lot farther.

HICKS: Early golfers using smooth golf balls realized that the more they used a ball, the farther it would go.

QUINTAVALLA: The reason for that, they quickly discovered was that the surface gets scuffed and knocked about. They started figuring out, hey, we're going to put round impressions, round dimples in.

HICKS: As a golf ball flies through the air, the airflow interacts with the surface of the ball and can greatly affect the amount of drag.

QUINTAVALLA: The wind is meeting the surface here and pushing against it. And then wrapping around.

HICKS: If the golf ball were smooth, the air flowing closest to the surface of the ball would follow the flow of air around it, creating a detached airflow behind the ball.

QUINTAVALLA: As air flows around the smooth golf ball, it becomes detached. The air that's closest to the surface doesn't want to stick to the surface, it wants to stick to the fast-moving flow.

HICKS: The detached flow causes a wake to form behind the ball which creates a low pressure zone. This zone is what causes drag.

QUINTAVALLA: That's almost like a vacuum, that's sucking the ball back and slowing it down in the face of the wind.

HICKS: Adding dimples to the ball changes how the air flows over it. As the air travels over one of the dimples, a tiny pocket of turbulence, or air disturbance, is created on the surface.

QUINTAVALLA: It tries to go in and then has a region where it's actually detached, but then by the time you get to the next dimple in the ball, it reattaches itself. And in the process of that detachment-reattachment, that's what creates the turbulence.

HICKS: Instead of impeding the flight of the ball, these tiny pockets of turbulence allow the closer layer of air to travel tighter around it.

QUINTAVALLA: Because these dimples have caused some low-level turbulence, it's mixing the high speed air from out here, and bringing it close to the ball so that that flow can remain attached to the ball.

HICKS: A more attached airflow creates a smaller wake, and thus a smaller low-pressure zone, which means less drag. Even this slight change can make a big difference.

QUINTAVALLA: A golf ball with dimples will go almost twice as far as the golf ball without.

HICKS: The dimples also aid the flight of the ball by influencing the lift as the ball spins through the air. Lift force is a result of a concept in aerodynamics known as Bernoulli's principle. The principle states that as the speed of the air flow is increased, the pressure of the air flow on the ball is decreased, creating lift. The lift is pronounced due to the dimples on the ball, which measure only fifteen-hundredths of a millimeter. Though tested for their effect, the USGA does not regulate golf ball dimples.

QUINTAVALLA: You can have any number. You can have really any shape. What we measure is the effects of dimples.

HICKS: These effects are tested and measured at the USGA's 70-foot indoor test range in Far Hills, New Jersey. Golf balls are launched through a series of sensors at upwards of 190 miles per hour.

QUINTAVALLA: These infrared sensors that we have can minutely track the trajectory of the golf ball, and do it with such precision that we can use computers to figure out how much aerodynamic lift and drag force each type of dimple pattern produces.

HICKS: While dimples' sizes, shapes, and effects may differ, they remain a crucial aspect of all golf ball designs.

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