Voice over: Michael Robles Written: Emma Haviland-Blunk Video and pictures: United States Golf Association (USGA) https://www.youtube.com/watch?v=fcjaxC-e8oY 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: ###