We all love when Sachin hits “it” with mighty power into the stands and adore “it” when Pathan swings “it” to get the first wicket for India. I am here to elaborate some interesting aspects of that “it”, i.e the cricket ball.
Cricket balls takes the center most position whenever a cricket match is played. As a cricket fanatic I always wanted to know the physics behind the swing of the cricket ball.
Does it really matters that how a cricket ball swings? Well, it matters because the science dictates it.Of course, bowlers do not have to know or understand the science, but I’m sure they would appreciate knowing the science behind the swing.
Since there have been many controversies over ball-tampering in international cricket, the subject of how a ball is made to swing has been of considerable interest. Here is my article to give a clearer understanding of the swing of the cricket ball.
Before talking about the swing of the cricket ball, I wish to give you a small introduction about the cricket ball.
All cricket balls are made up of cork, with leather on outside and inside layered with latex rubber. They are made of either two or four pieces which are stitched to form seam. The seam has usually six rows of stitches with around 80 stitches in a single row.
The resistance of air molecules when a cricket ball passes through the air on its way to the batsman creates what Rabindra Mehta, a NASA scientist, calls “a boundary layer” around the ball’s surface. It is not possible for the boundary layer to travel all over with the ball. At some point it definitely separates and that point is called as the flow separation. To make a ball swing there must be pressure difference which is determined by the flow separation.
The early flow separation creates high pressure and the late flow separation creates less pressure which causes a pressure difference and makes the ball to swing.
The boundary layer has two states.
- Laminar flow
- Turbulent flow
Laminar is the flow which is very smooth and its flows without any disturbances, like the water coming out from the pipe. Turbulent flow is the opposite of laminar flow.
The position of the seam is very important. When the cricket ball takes its flight in air and if the position of the seam is not deviated, then laminar flow is said to occur on both sides of the ball. The maximum swing is produced in a ball when it is shiny on both sides and new.
With seam position being straight, let’s understand the cricket ball’s swing.
The smooth side of the ball has laminar flow and the rough side has a turbulent flow.Pressure reduces on the rough side due to the turbulence and the flow seperation point is seen here.Gradually more pressure is created on the smooth side.A difference in pressure is created and the ball swings.
Coming back to the age old habit of keeping one side of the ball rough and polishing the other side of the ball. This method also induces swings of the cricket ball but many misunderstand them. I will rather not call it a misconception because bowlers and even fielders apply sweat or saliva which makes the ball heavy on one side which helps to induce reverse swing.
Thus I hope that I have given a clear view of the science behind the swing. This is my understanding but feel free to point out if there are any flaws.