This article explains how the numerous grooves on the surface of a golf ball improve its distance and athletic performance, and how this design plays a role in hydrodynamics.
The modern world is obsessed with ball sports. We cheer for Messi or Ronaldo’s exquisite shots, marvel at Ryu Hyun-jin’s hard-hitting fastballs, and hold our breath for Tiger Woods’s incredible driver shots. We pay attention to and love the movement of the ball, but some of the balls used in the sport of ball games are unusually shaped. While most balls are smooth or contain a few strings, golf balls are different. Golf balls have more grooves than you can count on ten fingers. Some people compare them to the threads on a baseball, the rubber on a tennis ball, or the seams on a soccer ball, but when you consider the relative sizes of the balls, golf balls have a much larger percentage of grooves than other balls.
In fact, golf ball grooves are closely related to the history of the game. Golf began to be known among the European aristocracy in the 16th century. The first golf balls were common, smooth, spherical balls made of wood. However, when the durability of the wooden balls became a problem, round balls made of cowhide were used. But here”s where we found a mystery. A bumpy, slightly dented ball that had been used for a long time traveled much farther than a new, smooth, perfect ball. This discovery caused great curiosity among European aristocrats. In most ball sports, newer balls are better than older ones.
The people who solved this problem were the golf ball makers’ researchers, who were mechanical engineers. One of the important fields of mechanical engineering is hydrodynamics, which is the study of the properties of fluids. This allowed the mechanics to analyze the movement of the golf ball. This phenomenon can be explained simply by understanding “the drag force acting on a moving object in a fluid”. A drag force is a resistive force that impedes the motion of a moving object, the most common example being friction.
Drag forces in fluids can be broadly categorized into two types: shape drag and friction drag. Shape drag is the resistance caused by pressure differences acting on a moving object. For example, when you run a 100-meter race, the air pressure in the front of your body is higher and the pressure in the back is lower, which is called shape drag. Frictional resistance, on the other hand, is the resistance caused by the viscosity of the fluid. The reason honey flows slowly down a comb is because of its high viscosity, which acts as a resistance to movement. Gases like air are less viscous, so the frictional resistance of an object moving in air is very small and virtually negligible. Therefore, we only need to focus on the shape resistance of a golf ball.
As the ball flies, the air flows along the surface of the ball and at some point starts to move away from the surface. When a smooth ball is moving through the air, the flow of air along its surface is straight. This is called laminar flow. However, when the air leaves the surface from the middle of the ball, the velocity of the air drops dramatically at the back of the ball, causing separation. Separation is the separation of the air into two layers, and as the air flow weakens, the air pressure decreases. A smooth ball flies a relatively short distance because the pressure difference between the front and back of the ball is large, which increases the drag of the shape.
On the other hand, a ball with a grooved or bumpy surface creates turbulent flow. As the air moves through the grooves in the golf ball’s surface, it no longer flows in a straight line. In the case of turbulent flow, the air flow is curved and delamination occurs at the back of the ball. This causes the pressure differential to decrease and the shape drag to decrease, so the golf ball travels farther.
Eventually, grooves on the surface of the golf ball reduce the drag on the ball, and the ball flies farther. In this way, engineering knowledge permeates our daily lives and will continue to have an increasing impact in the future. This is because engineering knowledge is not just a theory, but a great tool to understand and analyze the world we live in.
