The Secret Reason Why Golf Balls Have Dimples
If your ball didn't have them, it'd travel half as far.
On the green, everyone wants to believe they have the perfect technique down pat—and the gear to match. They've got the swing tuned to perfection, they brag about the brand of ball they use, their clubs are the best money can buy. But at the end of the day, physics has as much to do with golf as money and boasting do. It wouldn't matter if you had the perfect swing, club, and mindset without one key factor: the dimples on a golf ball.
The moment of impact between the club and the ball lasts for a fraction of a second, and that impact establishes the ball's velocity, launch angle, and spin rate. So yes, that split second is important, and you should definitely keep working on the exact right swing to make the impact count. But after the moment of connection, it's time to let gravity and the mystery of aerodynamics go to work. That's where the dimples come in.
The Short Answer
The dimples on a golf ball, and the pattern they are in, influence the aerodynamics of the ball. Optimizing the shape of the ball by creating those little pock marks changes how it flies through the air, which gives you a better shot at that hole in one. Adding dimples to golf balls creates a thin layer of air that sticks to the surface, minimizing the drag behind the ball and increasing the lift of the ball—allowing it to go higher and move forward faster.
As Tom Veilleux, a senior scientist, and Vince Simonds, director of aerodynamic research, at the Top-Flite Golf Company told Scientific American, "A smooth golf ball hit by a professional golfer would travel only about half as far as a golf ball with dimples does."
Golf balls weren't always this well-designed; in the days of yore, golf balls were made out of wood. And, in the 17th century, they were a specialty item made out of leather and stuffed with goose feathers, says Steve Quintavalla, a United States Golf Association engineer. By the 1900s golf balls were being made out of a tree sap called gutta-percha, which bounced better than the "featheries" of the 1600s. These "gutties" traveled farther as they became pockmarked and scuffed up from play, and thus the idea of adding dimples to golf balls was born.
The Heady Answer
So, how exactly do the dimples affect the flight of a golf ball?
Let's start off with the facts: golf balls have around 300 to 500 dimples, of about 0.010 inch in depth. The dimples are traditionally spherical, though other shapes can be optimized for aerodynamic performance, too: the Callaway HX utilizes hexagons, for instance, and this change was a big deal when the new ball was announced in 2002.
Getting more into the nitty gritty, we need to understand some key ideas of aerodynamics—primarily, lift and drag, the two components of the force exerted by air. Drag directly opposes motion, while lift is a perpendicular force that helps, well, lift the golf ball into the air. The goal is to increase lift and decrease drag to make objects go farther, and the dimples help do that.
As the golf ball flies, it's pushing air out of the way, creating a turbulent wake behind it where the air flow is agitated and has a lower air pressure. Quintavalla says the low-pressure zone causes drag because it acts almost like a vacuum, sucking the golf ball backwards.
The dimples create tiny pockets of turbulence; these allow the air flowing past the ball to travel more tightly around the golf ball as an attached airflow, minimizing the low pressure zone and the overall drag. The attached airflow creates a narrower low-pressure wake, which means the ball isn't sucked backwards as much. Effectively, the thin air cushion (the turbulent boundary layer) means that a dimpled ball can have about half the drag of a smooth ball, and can travel almost twice as far.
If you're more of a visual learner, here's Quintavalla laying out the physics with the help of diagrams:
Dimples also optimize the lift force, another piece of the aerodynamic puzzle. Put simply, the backspin on a golf ball redirects the air downwards as it moves through it, which produces a force upwards (remember: that's lift) thanks to Newton's 3rd Law (every action has an equal and opposite reaction, in case you need a reminder of that high school physics).
As the ball spins backwards, the top edge rotates in the same direction as the airflow that's moving over it. Because of friction, that airflow over the top is dragged around the ball and downwards behind it. The bottom of the ball is spinning in the opposite direction as the air flow, though, and can't be deflected upwards, so an area of high pressure builds up. Since the air from the top is being deflected downwards, there needs to be an equal and opposite force upwards from that high-pressure area (thanks again, Newton's 3rd), which is also known as the Magnus effect. This pressure imbalance creates lift, and the dimples on the ball exaggerate those effects.
So the next time you head out to the course and want to impress your buddies, you could definitely go into the Magnus force and its effect on backspin. You could just say that the dimples on a golf ball reduce the aerodynamic drag on the ball and increase its lift, making it go farther, faster. Or, you could hide the truth and stick with a classic brag. And if you're looking for greens to play on, here are the The 9 Hardest Golf Holes in America.
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