What is swing bowling?
The essence of swing bowling is to get the cricket ball to deviate sideways as it moves through the air towards or away from the batsman. This non-linear flight is mainly due to the aerodynamics of the cricket ball. In order to do this, the bowler makes use of five factors:
- The raised seam of the cricket ball
- The wear and tear on the ball
- The polishing liquid used on the ball
- The speed of the delivery
- The bowler's action
James Anderson's Banana Swing
Banana swing is referred to a "fast swinging yorker" ball which follows a path similar to a typical banana which looks like a 'C' shaped. Bowling a yorker itself is very difficult and bowling it in shape of banana makes it nearly impossible. Watch this awesome video to see physics in action!
How does a ball swing?
Swing is the sideways movement of the ball while it travels through the air towards the batsmen. While swing in tennis and golf ball is mainly due to its spinning (Magnus effect), swing in cricket ball is due to the asymmetric flow caused by the presence of seams. A cricket ball generally has six rows of seam, three rows in either hemisphere, with 80-90 stitches encircling the whole ball.
If the ball is delivered at a seam angle to the initial line of flight, the laminar flow over the ball is converted to turbulent flow on one side of the ball due to the presence of the seam while other side remains laminar. This asymmetric flow over the ball creates a pressure differential and the ball experiences a side thrust which deviates from its original line of flight and produces swing. This is called conventional swing which is achieved by maintaining laminar flow on the non-seam side and turbulent flow on the seam side facing the batsmen.
As the flow on the seam side facing the batsman turns to turbulent, the boundary layer associated with it separates later than the laminar boundary layer due to its increased energy causing a pressure differential across it, and thus causing the swing.
Like that wasn't enough!
In the mid 1980’s, the bowlers started to produce a newer version of swing bowling, especially with the old ball. It was popularly termed as reverse swing as it swings in the reverse direction of the conventional swing having the same seam orientation.
At the beginning, as the reverse swing is generated with the old ball only, it was initially believed that, to produce reverse swing, one side of the ball should be smooth and other side should be rough.
To generate reverse swing with an old ball, the non-seam side facing the batsman should be rough while the seam side should be smooth. Similar to the conventional swing, the seam trips the flow from laminar to turbulent, but this time the flow in the non-seam side also becomes turbulent due to its higher surface roughness. If the turbulent air flow in the seam side separates earlier than the turbulent flow on the other side, the pressure differential now acts on the opposite side giving rise to reverse swing. Traditionally, reverse swing occurs when half of the ball is has been naturally worn significantly. In most cricket matches, the phenomenon of reverse swing occurs after 40 or more overs!
We're sure the next time you're in the playground bowling that crucial over, the opponent will not see this coming!
Image source: Crictracker.com
Content source: The Swing of a Cricket Ball – A Computational Study
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