Probing Question: How do dimples make golf balls travel farther?

Jun 21, 2007

A golfer's worst enemy may be divots, but his or her best friend may be dimples -- the dimples on a golf ball that send it sailing farther down the fairway.

"In the early days of golf in Scotland, golfers discovered that their old golf balls went farther than the new, smooth ones," said Mark Maughmer, professor of aerospace engineering at Penn State. The beat-up balls reacted differently to the forces they encountered while flying through the air, Maughmer explained.

It wasn't long before golfers were intentionally pitting their brand-new balls to improve their games. By 1905, golf balls were being manufactured with dimples, as they have been ever since.

What's the magic in those dimples?

All flying objects are subject to the forces of lift and drag, Maughmer explained. An airplane produces lift when the air flowing over its wings is forced downward, causing the plane to rise. At the same time, the plane's forward motion creates drag or resistance.

A golf ball can produce lift in a similar fashion. For example, if a struck ball has backspin, which changes the flow of the air around the ball, it produces lift, a force that is perpendicular to its flight path. As Maughmer explained it, this is a result of high pressure being created at the bottom of the airborne ball relative to its top, and the lift, he said, is a consequence of these differences in pressure.

At the same time, the struck ball also experiences drag, a retarding force that acts in the direction opposite to the direction of its flight path. Part of the drag force is due to the flow not being able to stay attached to the surface and "come together" on the back side of the ball. This "separated flow" forms a low-pressure wake behind the ball, and the difference between these pressures and the higher ones found on the front of the ball produce what is termed "pressure drag."

The other part of the drag force experienced by the ball is due to "skin friction," a tendency to pull the air nearest its surface along with it. "It's just air rubbing on an object, which retards its motion," Maughmer says.

Skin friction depends largely on the pattern of airflow in the boundary layer very close to the surface of the ball. If the flow is smooth, or laminar, it has lower skin friction, but is less able to stay attached to the rear surface of the ball. A turbulent boundary layer, however, although having more skin friction, is better able to stay attached to the back of the ball. That, Maughmer said, is where the dimples come in.

"By putting the dimples on a golf ball, I force the boundary layer to transition from a laminar one to a turbulent one," he explained. The greater "mixing" of air in the turbulent boundary layer allows passing air to cling to the flying ball a little bit longer before it separates, which in turn narrows the ball's wake, the region of low-pressure air created behind it. A smaller wake means less air pressure pulling on the back of a golf ball as it sails toward the green.

In effect it's a positive trade-off: "The ball pays a skin friction penalty, but gains a pressure drag advantage," Maughmer said. The difference is huge in terms of the distance a golf ball can be driven, he adds. Dimpled balls can travel nearly twice as far as smooth ones.

As an aerodynamicist, Maughmer admitted, he's somewhat limited in how much he can engineer a small, round object. "I can't mess with the shape of a golf ball," he said. "For something this size, shape and speed, dimples are the optimal solution."

Source: By Mike Shelton, Research Penn State

Explore further: Diamagnetic levitation of pyrolitic graphite over a single magnet achieved

add to favorites email to friend print save as pdf

Related Stories

Introducing the multi-tasking nanoparticle

1 hour ago

Kit Lam and colleagues from UC Davis and other institutions have created dynamic nanoparticles (NPs) that could provide an arsenal of applications to diagnose and treat cancer. Built on an easy-to-make polymer, these particles ...

Eta Carinae: Our Neighboring Superstars

1 hour ago

(Phys.org) —The Eta Carinae star system does not lack for superlatives. Not only does it contain one of the biggest and brightest stars in our galaxy, weighing at least 90 times the mass of the Sun, it ...

Indonesia passes law to tap volcano power

1 hour ago

The Indonesian parliament on Tuesday passed a long-awaited law to bolster the geothermal energy industry and tap the power of the vast archipelago's scores of volcanoes.

Recommended for you

Awakening the potential of plasma acceleration

23 hours ago

Civil engineering has begun for the new Proton Driven Plasma Wakefield Acceleration Experiment (AWAKE) at CERN. This proof-of-principle experiment will harness the power of wakefields generated by proton ...

Magnetic memories on the right track

23 hours ago

Computer hard drives store data by writing magnetic information onto their surfaces. In the future, magnetic effects may also be used to improve active memory in computers, potentially eliminating the need ...

When an exciton acts like a hole

Aug 27, 2014

(Phys.org) —When is an electron hole like a quasiparticle (QP)? More specifically, what happens when a single electron hole is doped into a two-dimensional quantum antiferromagnet? Quasiparticle phenomena ...

User comments : 0