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Introduction There are three types of swing bowling:-

Conventional swing

Reverse swing and

Contrast swing.

In the past few years cricketers have been bombarded with newmethods of the ball’s deviation through the air, but very candifferentiate between the physics of each. One of the few men isRabindra Mehta, a NASA scientist and former club fast bowler based inCalifornia, who has studied cricket-ball aerodynamics for nearly threedecades.

Swing Bowling The term Swing Bowling is used in Cricket for a type of ball bowled byfast or medium pace bowlers to the batsman.The Philadelphian’s BartKing helped to perfect swing bowling in the early 20th centaury.

Why Does A Cricket Ball Swing The aerodynamics of swing is that the wind moves very close to theball towards the shiny portion and disturbs over the seam on the other

side of the ball at a distance, creating a vacuum area. So the processof the ball moving towards the vacuum side is ‘Swing’. This processinfluences the ball many a times in the 22 yards distance. Thereforethe coaches advise the bowlers to release the ball and make aparabola in the air and not to press or hit the ball on the ground, i.e.low trajectory, to induce the air on the ball.

 The essence of swing bowling is to get the cricket ball to deviatesideways as it moves through the air towards or away from thebatsman. In order to do this, the bowler makes use of four factors:

The raised seam of the cricket ball

Asymmetry in the ball caused by uneven wear of its surface

 The speed of the delivery

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 The bowler’s action

 The asymmetry of the ball is encouraged by the constant polishing of one side of the ball by members of the fielding team, while allowing

the opposite side to deteriorate through wear and tear. Over time, thisproduces a marked difference in the aerodynamic properties of the twosides.

At speeds around around 130 km/h the airflow around the ball is intransition between smooth, or laminar flow, and turbulent flow. Atspeeds of 145 km/h and above, all the flow is turbulent. A medium-pace bowler, working at 120 to 130 km/h takes advantage of this. Inthis critical region, the raised seam and other minor imperfections inthe ball’s surface can induce turbulence while air flowing over otherparts of the ball remains laminar. Turbulent air separates from thesurface of the ball later than laminar flow air, so that the separation point moves to the back of the ball on the turbulent side. On thelaminar flow side it remains towards the front. The result is a net forcein the direction of the turbulent side. Thus by keeping the seam androughness to one side, the bowler induces the ball to swing in thatdirection. Skilled bowlers can even make a ball swing one way, andthen ‘break’ the other way upon bouncing, with an off cutter or legcutter hand action.

Swing Bowling- New Ball

1 The brand new ball do swing2 It is against the Bernoulli’s Principle, The ball swings towards therough side

3 The seam is mostly not vertical but tilted

4 If the air friction is too much it should cause the spin on the ball.

5 Even an irregular stone would swing like this.

Conventional SwingA swing bowler aligns the seam and the sides of the ball to reinforcethe swing effect.

Inswing

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An inswinger is bowled by holding the cricket ball with the seamvertical and the first two fingers slightly across the seam so that it isangled a little to the leg side. Once the ball has worn and beenpolished so that one side is rougher than the other, the rough side isplaced on the leg side. The ball is placed on the pad of the thumb. This

thumb position locks the wrist in a position inclined to the leg side.Inswing can be bowled from side-on, mid-way or chest on positions. Itis the wrist position that is crucial, not the position of hips orshoulders.When the bowler delivers the ball, he angles the seam sothat it points slightly to the leg side. To help achieve this position thebowling arm should be near vertical, brushing close to the ear. Atrelease the wrist should remain cocked so as to help impart backspinalong the orientation of the seam. The angle of the seam to thedirection of motion produces an aerofoil effect as the ball movesthrough the air, pushing it to the leg side. This is enhanced bydifferential air pressure caused by movement of air over the rough and

smooth surfaces, which also tends to push the ball to the leg side. Theresult is that the ball curves, or swings in to the batsman.

OutswingAn outswinger is bowled by holding the cricket ball with the seamvertical and the first two fingers running along either side of the seam.Once the ball has worn and been polished so that one side is rougherthan the other, the rough side is placed on the left. When the bowlerdelivers the ball, he angles the seam so that it points slightly to the leftas well, and releases the ball rotating about a horizontal axis with theseam along the rotational “equator”. The angle of the seam to the

direction of motion produces an aerofoil effect as the ball movesthrough the air, pushing it to the left. This is enhanced by differentialair pressure caused by movement of air over the rough and smoothsurfaces, which also tends to push the ball to the left. The result is thatthe ball curves, or swings to the left.

From a right-handed batsman’s point of view, the swing is away fromhis body towards the right, i.e. towards the off side. This swing awayfrom the body is the source of the name outswinger. To a left-handedbatsman, the swing is in towards the body and towards the leg side.

Outswingers are considered to be one of the more difficult fast

deliveries for a right-handed batsman to play. This is because the ballmoves away from his body. This means that any miscalculation canresult in an outside edge off the bat and a catch going to the wicket-keeper or slips fielders. Also, outswingers often mean the batsman hasto swing his bat away from his body, so an inside edge can ricochet onto the wicket and get him out bowled.

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Physics Of Outswing1. Shine the cricket ball with spit on one side so that it is more aero-

dynamic through the air than the rough side

2. Have the seam at an 20 degree angle with it facing away from thebatsman.

3. When you bowl, try and get the ball to pitch on middle and off andon the same length as a normal delivery.

Reverse SwingFormer Pakistan international cricketer Sarfraz Nawaz was the founderof reverse swing during the late 1970s, and he passed his knowledgeon to former team-mate Imran Khan who in turn taught the duo of Wasim Akram and Waqar Younis. The English pair of Andrew Flintoff  and Simon Jones are also well known for the ability to reverse swingthe ball having been taught by Troy Cooley . The Indian pace duo of Zaheer Khan and Ishant Sharma, coached by Venkatesh Prasad, usedreverse swing, which enabled India to win the home series againstAustralia in 2008.Normal swing occurs mostly when the ball is fairlynew. As it wears more, the aerodynamics of the asymmetry changeand it is more difficult to extract a large amount of swing.This is knownas Reverse Swing. Andrew Flintoff and Simon Jones have been known

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to produce reverse swing in balls as young as 15 overs old. ZaheerKhan and Ishant Sharma of India also managed to get the reverseswing as early as just 8 overs. In essence, both sides have turbulentflow, but here the seam causes the airflow to separate earlier on oneside. The result is always a swing to the side with the later separation,

so the swing is away from the seam.Reverse swing is difficult to achieve consistently, as it relies on unevenwear of the ball, tends to occur mostly in hot, dry weather conditions,and requires bowling at high speed. Normal swing can be achieved atrelatively moderate bowling speeds, but only the fastest bowlers canregularly produce reverse swing.

With an older ball, the ball will swing into the batsman if you keep theball in the out-swing position; this is called reverse swing and is a verycomplex but effective delivery that requires much pace and a certainbowling action.

Contrast SwingHowever, the ball generally had the seam straight up (not angled) andswung towards the smooth side. This was obviously not reverse swingand it was somewhat difficult for me to explain to the bowlers andcoaches what was going on. That is when I developed the new term:“contrast swing.” So how is contrast swing different from conventionaland reverse swing? For one thing, the swing direction is determined by

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the bowling speed, as opposed to seam and smooth/rough surfaceorientations.

In Figure 4(a), a ball with a contrasting surface roughness is flyingthrough the air at a relatively low speed with the seam straight up. Inthis case, the boundary layer over the upper surface separatesrelatively early in a laminar state while that on the bottom rough sidebecomes turbulent and separates later. This asymmetry results in aside force which makes the ball swing towards

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the rough side.

If the ball is released at a much higher speed, the flow field is differentas shown in Fig. 4(b). In this case, transition occurs on both sides of theball, but the turbulent boundary layer along the rough bottom surface

is thickened and weakened (in the same way that the seam weakensthe turbulent boundary layer in reverse swing). As a result theboundary layer on the rough side separates relatively early and theball now swings towards the smooth side.

 The most exciting feature about contrast swing is that just about anybowler (regardless of bowling speed) can implement it in practice. Asmost cricketers are aware, it is much easier to release the ball with theseam straight up, rather than angled towards the slips or fine leg. Thus, even mere mortals should be able to swing such a ball, and ineither direction, since the bowling action is the same for both types of swing, the only difference being the orientation of the ball.

Late Swing There are several possible explanations for late swing - where

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sideways movement occurs only late in the ball’s flight.

i). It is an illusion. The flight path of a ball with a constant sideways-acting force applied to it is parabolic: the amount of the sidewaysmovement naturally increases along the flight path.

ii). The ball is initially above the transition speed for turbulent flow onthe shiny, non-seam side, but drops below this threshold as itdeccelerates in flight, particularly after bouncing, initiating late swing.

iii). The ball rotates slightly in flight, with the seam becoming angledand thus initiating late swing.

Some More Points On Physics Swing Bowling

Humidity: Despite being widely observed in practice, there is currentlyno theoretical, or experimental, evidence for humidity having anyaffect on the amount of swing. Humid air is less dense than dry air -although the difference is minimal - and so would be expected toinduce less swing. Experiments in wind tunnels show no noticeabledifference in the amount of swing between dry and humid air, andthere is no measureable aerodynamic difference in the state of the balldue to moisture.