You'd think a totally smooth surface would be better at flying through the air with the least amount of wind resistance. So why do golf balls have all those little indentations? So they can use the air against itself.
Ah, golf, the thing you watch when nothing else is on and you're not energetic enough to get off the couch. Since putting is never interesting unless the golfers are trying to time it so they don't get their balls knocked aside by a windmill, and the audience isn't privy to the whispers about which kind of club the golfer will use, the whole draw of the sport is pretty much seeing a clean white ball flying through the vast blue sky.
So it's no wonder that golfers will do everything they can to make the ball go farther. Once upon a time, the only balls that went far were the ones that weren't so white. Golfers noticed that battered balls went farther than new, smooth ones, and the balls were modified accordingly, if bemusedly.
It doesn't make sense. Air generally moves smoothly over smooth surfaces. A smooth ball should fly easily, the air parting and rushing past it without any turbulence.
A rough surface doesn't make for easy airflow. Air dips into crevasses and is stopped short. It eddies and whirls. It creates turbulence, which sucks the ball one way and pushes it another, making it erratic and slow. After all, you don't see any pits being put into the wings of airplanes to make them fly faster.
You do see airplane wings tapering off, though, and that makes all the difference. The wing tapers off behind, providing air a smoother path to move over. And of course a wing keeps a flat underside, for that all-important lift. The ball doesn't do the same. As a smooth ball moves through the air, it clears a path of air behind it as wide as it is, and then it abruptly drops away. This leaves a wide wake and this wake can do many unpleasant things a ball in flight. It can create pockets of low air pressure, or extremely fast-moving, swirling vortices. Both ‘suck' the ball backwards, draining its momentum.
Rougher balls, on the other hand, create their own turbulence right off the bat. The dimples and bumps create their own little pockets of suction, and their own small breezes that push at the ball. Both of these things keep a layer of air in contact with the ball. Specifically, they keep that layer in contact with the side of the ball that trails behind. This creates a sort of glove of air around the ball and makes for a much smaller wake. That smaller wake pulls the ball back less, and lets it fly farther.
This is counter-intuitive, but far less counter-intuitive than the sport of golf allowing the ball to be modified in the first place. For a game that goes to literally great lengths to make every aspect as challenging as possible, modifying the ball seems like cheating. I wonder how golfers were convinced to do it. I wonder if we can convince them to add rocket packs to the balls, next.
Via LiveScience and HowStuffWorks.