Have you ever wondered why a golf ball looks like a shrinking powdered Munchkin from Dunkin Donuts? Of course you have— so have I. And as with almost every sports-related question, there is a surprising amount of science to explain why golf balls have dimples. In a funny, accidental way, the aerodynamic answer weaves itself through a short history lesson.
Information relating to the materials in golf balls is infinite, but I want to focus on the incredible progression of shape they have endured. To put any crazy thoughts to rest, golf balls have always been round (sadly). A sphere is probably the most ideal shape for golfing: it can be fairly aerodynamic (more on this later), has a strong mechanical structure, and is completely symmetrical so can handle various spins identically. However, to put it bluntly, golf balls used to look like dumplings that had been hand-squeezed into a crude spheres. Don’t believe me? Check out these beauties:
Effectively, this is our starting point: a crude sphere with large seams and certainly some blemishes. “Well what if we could make it more spherical and smoother? That would help it go farther,” thought every golfer in the 1800s (and me). Well, at least half of this statement is true. More “spherical” spheres certainly make for better golf balls, but should they be smooth as well?
Practically by accident, golfers around the world answered this question on their own. Beginning in the mid 1800s, golfers began to use the first “Gutties” — smooth golf balls made from a dried resin. Interestingly, and almost shockingly, the balls seemed to perform better with age: the more scrapes and nicks they had, the further they flew as long as they maintained a proper spherical shape.
And VOIALA, science had made a grand entrance into golf but may not help this guy with his putting:
“But how? Why does a golf ball with blemishes fly further?” wondered those same golfers in the 1800s (and me, still).
Luckily (but actually unluckily, because it would be cool), the answers to this question come from fluid dynamics, and not from black magic (so cool). The wear and tear that golfers were imparting on their equipment was was actually producing a very real change in the way that the balls interacted with the air as they passed through it. They were accidentally reducing the drag on their golf balls, which increased fly time and distance. [Obligatory link to “blunt” object drag]
What the old golfers had discovered by accident, and what we can now show experimentally, is that a golf ball with imperfections creates a turbulent boundary layer to decrease overall drag. Now this is a lot to take in, but it basically boils down to a few connected phrases. The first is the “boundary layer” of the golf ball. In essence, the air that is being “dragged” along by the ball as it flies (due to viscous, and other effects), it the boundary layer. The second important phrase is “turbulent.” Turbulence indicates that the air being displaced and “dragged” by the ball moves in seemingly random, erratic directions all around the ball as it is displaced. This is different from a “laminar” flow which is has very straight, striated air flow (The two different flow types are visible in the image above).
Effectively, a turbulent flow separates from any given object “later” than a laminar flow would. A separation of the flow (and boundary layer) from the ball results in pressure drag which manifest as the creation of a wake. Visually, a wake, can be most easily seen and visualized with boats, rather than airborne objects. The larger the wake, the more water (or any fluid) you are displacing, which requires additional power since you are moving mass . In flight, the absolute randomness of a turbulent flow helps the boundary layer “stick” to the ball for longer, resulting in a decreased wake size and less pressure drag. There are many, many articles explaining the hard science behind drag reduction due to turbulence if you want to learn more.
So next time you have a golf ball and it feels like a round swiss cheese, remember that those little indentations are making that ball, the plane you fly in, and the obnoxious boaters on your favorite lake go just a little bit faster and farther (And you have some frugal golfers from the 1800s to thank for your 250 yard drive).