How does cricket ball swing

         

                So really how does a cricket ball swing? the answer lies in the aerodynamics of physics. Basically there are three types of swings
1) In-swing - In this type of a swing the ball goes towards leg stump after it pitches , One has to keep rough side of the ball on the right hand side.At the same time the seem position inwards.
2) Out swing - In this type of the swing the ball goes towards the sleep corner after it pitches. One has to keep rough side of the ball on the right hand side. At the same time seem position outwards
3) Reverse swing -In this type of the swing the ball does exactly opposite phenomenon than the above two cases . One has to keep the shiny side of the ball on the right hand side in order to get reverse in-swing and vice verse.
                   Let us physically examine what exactly happens in the process of swing bowling . For that I will take the example of conventional out swing.
1) Conventional out swing- In this category bowler keeps the ball slightly angled towards the sleep corner and rough side on the right hand side as shown in figure below.

                     There are two concepts which needs to be understand, the first one is laminar flow of air. In this the movement of air is smooth and air sticks to the ball for shorter time as surface is smooth and hence separation of the air from the ball is earlier. On the second hand there is rough side so the movement of air is disturbed or simply turbulent. In this case because air strips from the seem and sticks to the ball for longer time and separates later. So there is a low pressure on the top and high pressure at the bottom which results in the out swing because of of resultant force. The direction of the resultant force is as shown in the figure.

 2) Reverse swing-  The concept of reverse swing is a bit difficult to understand. Reverse swing starts happening around 30th over in the match. At this time the both side of the ball are rough. So the bowler can't take out the conventional swing but if someone starts bending his back and generating speed the ball moves exactly opposite of conventional swing.
 

                    In this case since there is turbulent flow of air on the both hand side hence a thick layer of air forms at the seem position at the top level. The resultant force now turns towards right and the ball moves in the reverse direction.
3) Straight seem bowling at high speed / contrast swing
                    In this case the seem is straight facing the batsman straight.At low speed the ball will move towards the rough side but at the high speed the ball will move towards the shiny side.

                   Same mechanism of aerodynamics also happens in this case. So the conclusion can be drawn that the effective swing bowling depends upon the bowling action of the bowler, the wrist position while delivering the ball  and most important the speed which one can generate. If the bowler can generate the speed up to 90 mph at the start, the ball will start reverse swinging from the first ball of the over.