Sky Has No Limits...! So Do I....!

I recently attended induction program, organized by "SHELL, shipping & trading". As a prize, for winning in an in-house quiz, I got a pack of golf balls. I opened the pack and saw three golf balls with SHELL'S logo embossed in it. This was the first time I have ever touched a golf ball with my hands and it looked very glossy. Even though I have watched numerous times in television, I have never thought of the "dimples" the golf ball has...! I play cricket and I thought "the cricket ball is smooth and well-rounded"," why not the golf ball?". This was the question eating my brain, till I got this explanation..

"why the golf balls have dimples in it?"

A ball moving through air, experiences two major forces. Lift & Drag.
Now lets first understand the aerodynamic action of lift and drag on a ball of smooth sphere(without dimples).The drag force has two components. One is the frictional drag, due to air resistance. This is very less and negligible. The main drag is created by the "Flow Separation" behind the ball, and is called as "Pressure drag" due to separation.


The figure shown beside, shows the travel of golf ball in air, with laminar flow. Don't wonder what is laminar flow...! In simple terms, a laminar flow is one without turbulence, or the air flowing around the ball has a very smooth layer. There is no disturbance or turbidity. So the flow separates easily and much earlier. The surface of the ball sphere is so smooth that it does not cause any disturbance of air flowing around it. This tends to keep the air flow layers separated.

The figure shown besides, investigates the travel of a golf ball with dimples on it. The dimples make the air flow turbulent. Each small unit of air collides with the dimples and encounters disturbance within them. This creates a turbulent flow around the golf ball. This turbulence, delays the flow separation. Thus from the figure, due to delayed flow separation, the region behind the golf ball is different from the one above.The separation region is smaller compared to laminar flow. This difference in flow separation delay, makes the golf ball with dimples fly farther. Thus the dimple design was adopted.


On further investigation, it seemed that the golf ball got its lift from the dimples.
As we all know, The LIFT is the force which causes the ball to elevate from the ground level. If the golf ball is given a proper spin, about the horizontal axis, then this makes the ball to rotate in counter-clockwise direction, making the air to go beneath the ball. Thus air acts as a step making the ball to climb over it. This can be understood from the smoke forming a layer beneath the ball in the picture shown below.

If the golf ball is hit with a spin around horizontal axis, such that the top of the ball coming towards the golfer, then it produces a lifting force. This is evident from picture, which shows the smoke goes beneath the ball, if the ball is hit in the direction of rotation as shown.

This type of spin is known as "Back Spin". In cricket, if a bowler spins the ball in this fashion, then it is called as top spin. This type of spin, increases the velocity on the top of the ball and decreases the velocity on the bottom part. Thus as per Bernoulli 's principle, as the velocity increases pressure decreases. Thus we can conclude that the pressure on top of the ball is lesser than when compared to bottom of the ball. This pressure difference causes a slight lift of the ball. This phenomenon is called as "Magnus Effect". This is also vital in swinging of the cricket ball.

And after understanding the above concept by studying various materials for more than half a day, I want everybody to understand this easily in few minutes. I believe that everybody understood the aerodynamics behind the golf ball easily. Comments are welcome for further discussions.