Why do golf balls have dimples?

Why do golf balls have dimples?

When it comes to sporting projectiles, Golf is King. But what about baseballs?Basketballs? Footballs? Tennis balls? Forget about it.Nothing but concoctions of skin, bark, and hair. Where's the technology? In golf balls, that's where. High technology materials engineered into high precision airframes with high performance flight capabilities. 

A golf ball's performance dwarfs that of anyother ball in sport:A child can easily hit one out of a Major League ball park and the average adult can launch one an eighth of a mile. What makes a golf ball fly like that? In a word, AERODYNAMICS. While other sporting projectiles push through the air, golf balls soar through it. 

Engineers and scientists in the golf industry study the impact between a golf club and a golf ball to determine the ball’s so-called launch conditions. The impact typically lasts only 1/2000 of a second, but it establishes the ball’s velocity, launch angle and spin rate. After this brief impact the ball’s trajectory is controlled entirely by gravity and aerodynamics -no matter how much the golfer hopes or curses. As a result, aerodynamic optimization-achieved through dimple pattern design-is a critical part of overall golf ball development.

A smooth golf ball hit by a professional golfer would travel only about half as far as a golf ball with dimples does. Most golf balls have between 300 and 500 dimples, which have an average depth of about 0.010 inch. The lift and drag forces on a golf ball are very sensitive to dimple depth: a depth change of 0.001 inch can produce a radical change to the ball's trajectory and the overall distance it can fly. Dimples have traditionally been spherical in shape, but it is possible to optimize the aerodynamic performance of other shapes. Callaway balls, for example, often use hexagons.

Air exerts a force on any object moving through it. Holding your arm out of the window of a moving car easily illustrates this phenomenon. Aerodynamicists break down the force into two components -lift and drag. Drag acts to directly oppose motion, whereas lift acts in a direction perpendicular to motion (it is usually directed upward in the case of a golf ball). As you rotate your hand in the air stream, you vary the amount and direction of the lift and drag forces acting on your hand. A moving object has a high-pressure area on its front side. Air flows smoothly over the contours of the front side and eventually separates from the object toward the back side.

A moving object also leaves behind a turbulent wake region where the air flow is fluctuating or agitated, resulting in lower pressure behind it. The size of the wake affects the amount of drag on the object. Dimples on a golf ball create a thin turbulent boundary layer of air that clings to the balls surface. This allows the smoothly flowing air to follow the ball's surface a little farther around the back side of the ball, thereby decreasing the size of the wake. A dimpled ball thus has about half the drag of a smooth ball.