Science of Swing Bowling

Swing Bowling is the technique used by bowler in cricket to decieve batsmen. It is classified as subtype of fast bowling.

The Aim of swing bowling is to move the ball in air towards or away from the batsmen.In hope that it would change its path in air, decieve the batsman and cause them to play it incorrectly.

Asymmetry of the ball is encouraged by the polishing of one side of the ball by members of the fielding team, while allowing the opposite side to deteriorate through wear and tear. With time, this produces a difference in the aerodynamic properties of the two sides.

Both turbulent and laminar airflow contribute to swing. Air in laminar flow separates from the surface of the ball earlier than air in turbulent flow, so that the 'separation point' moves toward the front of the ball on the laminar side. On the turbulent flow side it remains towards the back, inducing a greater lift force on the turbulent airflow side of the ball. The calculated net lift force is not enough to account for the amount of swing observed. Additional force is provided by the Pressure-Gradient force.

To induce the pressure-gradient force the bowler must create regions of high and low static pressure on opposing sides of the ball. The ball is then "sucked" from the region of high static pressure towards the region of low static pressure. A layer of fluid, in this case air, will have a greater velocity when moving over another layer of fluid than it would have had if it had been moving over a solid, in this case the surface of the ball. The greater the velocity of the fluid, the lower its static pressure.

Cold and humid weather are said to enhance swing. Colder air is denser and so may affect the differential forces the ball experiences in flight. Humidity up to 60-70% is the best for swing. Countries like England is best known for swing bowling as they have these overcast conditions.

An "outswinger'' to a right-handed batsman can be bowled by aligning the seam slightly to the left towards the slips and placing the roughened side of the ball on the left. This results in the ball moving into the 'off side'(away from batsman) while in flight.

An "inswinger" to a right-handed batsman can be bowled by aligning the seam slightly to the right and placing the roughened side of the ball on the right.This results in the ball moving into the 'leg side'(towards batsman) while in flight.

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For more info-: https://en.wikipedia.org/wiki/Swing_bowling                                                Source-: Wikipedia, ESPNcricinfo, Cricbuzz.