Why Does A Golf Ball Have Dimples?
By KorryFranke on 6/24/08
Long, long ago in a far away land (ok, not really long, long ago but more like the late 1800's) two golfers prepared to tee off on the first hole of their local golf course. The first gentleman opened a brand new box of his favorite golf balls and placed a pristine, white, smooth, spherical golf ball on the tee. Swinging the club with all his might, he crushed the ball, hitting it almost perfectly. It sailed down the fairway landing about 125 yards away.
The second golfer reached into his bag and could only find an old, scuffed up, dingy golf ball. With the first golfer snickering at this poor excuse for a golf ball, the second golfer placed it on the tee, brought his club back, and then swung with all his might, making perfect contact with the dingy ball and watching it sail far, far past the first golfers ball and landing well over 200 yards away.
While it was not really understood why the scuffed ball performed so much better than the smooth ball, word quickly spread and soon most golfers began to practice with new balls and play with scuffed practice balls. It would take over a quarter century before Taylor Hobson solved the riddle of why the rough balls traveled further and began producing dimpled golf balls... but the game of golf has never been the same since.
So why does a dimpled golf ball travel further than a smooth golf ball? The answer has everything to do with drag, even though that may seem a bit counterintuitive at first. As air moves past a sphere, two types of drag develop. The first is drag due to friction, or the drag of the air hitting the front of the ball. The second and more prominent type of drag, however, comes from the separation of the airflow behind the golf ball (see top of figure). As the air loses its ability to stick close to the ball (known as the boundary layer), it separates from the ball and creates lots of little eddies that basically try to pull the ball backwards. Thus, to make a ball fly further, the separation of the boundary layer must be delayed as long as possible. To do that, there are basically two options: increase the speed of the ball through the air (which isn't really possible since a player can only hit the ball so hard) or find a way to force the air to stay in the boundary layer longer. And that, Mr. Hobson discovered, could be done by roughing up the ball.
Why does a rough ball help delay airflow separation? The rough parts (or dimples) create very small amounts of turbulence near the ball's surface that actually add energy to the air in the boundary layer. More energy means more sticking power which means the airflow separation occurs later. The later the separation, the fewer eddies behind the ball thus decreasing the force trying to pull the ball backwards and allowing the ball to fly further. (See bottom of figure).
Obviously, the physics involved are more complex than this basic explanation, but hopefully you get the idea. Golf ball manufacturers are constantly doing more tests to figure out the ideal number of dimples, but it's generally accepted that between 300 and 450 dimples is ideal. The USGA also stipulates that the dimples must be symmetrically placed around the golf ball because asymmetrically placed dimples help to keep a ball spinning upright and thus nearly eliminate the chance for hooks and slices. Sorry about your luck... but maybe you can find some on eBay!
Email Korry your questions at firstname.lastname@example.org.
Korry Franke is a Boeing 757 and 767 pilot for Continental Airlines where he flies out of Newark, NJ to destinations across the US and around the globe. He lives in Bethlehem, PA where he spends most of his time on days off at the driving range or out on the golf course giving his game the practice it so desperately needs.
[ comments ]
El Presidente says:
Interesting...thanks for the education
I read somewhere that this aerodynamic phenomenon only works at golf ball speeds too; just in case you were wondering why our cars and jets don't have dimples on them.
Learjets have BLEs on top of the wings, Boundary Layer Energizers, They look like the speed bumps on a street. The leading edge of the wing has alternating flat head and round head screws also,for that reason. When you first see that mismatch, you'd think that the mechanic was just putting in whatever he found laying around.
Great one. Always wondered.
Korry, how in the world did you come to that conclusion? Did you beat up your airplane with a hammer thus creating dimples thus allowing airflow to increase your air speed? How many golf balls without dimples, and those with dimples, did you test? I hit perfectly smooth golf balls with a perfectly smooth (no grooves) sand wedge and they flew an average of 90 yards and stopped, with backspin, on the green. I hit dimpled golf balls with a square grooved sand wedge and could only get 70 yards out of them. No noticeable backspin. Not just one of each, but two dozen of each ball and each club. Same swing, same teeing area, same green, although I had to move 20 yards closer with the grooved sand wedge to reach the green. Man, am I confused and screwed! (More)
Were your tests attested and/or witnessed by anyone? Mine were, by a local PGA Professional golf pro who couldn't believe what he saw. So he hit the same clubs and same balls. His shots were longer, but the same results! Smooth balls, smooth sand wedge, same results. Dimpled balls, grooved sand wedge, a little better than mine, but he was a pro and could hit down on the ball much better than I. Yet, basically the same results. ?????? Oh well, who cares? I still use the Titleist 392 dimple ball and same old golf clubs, Titleist AP2 irons. I guess I'm not good enough to make any other informed opinion, except: Play with the equipment you feel most comfortable with. Or... fly with the same!
The REAL PapaJoe is going to be plenty mad when he sees the asinine comments made by this jerk using his name.
Thirsty Hursty says:
My understanding of the advantage of dimples comes from studying fluid mechanics at university. A textbook example showed how the dimples on a back spinning golf ball gives the ball lift and helps it to fly further. The friction of the dimples 'grabs' the air and sets it rotating about the ball. The rotating air beneath the ball collides with oncoming air and is slowed, where as the rotating air above the ball is helped along by oncoming air and moves faster. In all fluid mechanics high velocity results in low pressure and low velocity results in high pressure. Thus the dimples on a back spinning ball create high air pressure below the ball and low pressure above it. This gives the ball lift and it flies through the air further.....Usually! Too much spin and loft and you get what people refer to as ballooning.
Golfray you described yourself not PapaJoe. Can anyone explain how a golf ball
heading east, on a day with no "wind" can create "air flow" heading west? The university will take you to their multi-million dollar wind tunnel and show you a golf ball sitting still while they create a huricane size wind to travel past it.
Okay. But neither an airplane or a golf ball every saw the inside of a wind tunnel. So lets go to the golf course. Now explain how it happens, when their is no wind?
[ post comment ]