How does a cricket ball swing?

ক্রিকেট বল কিভাবে সুইং করে

How does the cricket ball swing? Can you tell what the cricket ball is made of? Do you know how a ball swings in a certain direction and what causes it? For those who don’t play cricket much, it might be a simple bat-ball game. However, those who know cricket see the game as a combination of basic mechanics plus strategy. In every single delivery, the ball can take a different trajectory based on the length, line, speed and swing of the ball.

imran khan bowling

It was former Pakistan fast bowler Imran Khan who introduced the concept of ‘reverse swing’ to the first ball in 1977. Everyone was confused about whether the matter was ball tampering or not. Because no one understood the ‘reverse swing’ of the ball. But why did no one understand the science behind the cricket ball swing or ‘reverse swing’ technique until scientists thoroughly researched it? In this blog, we are going to talk about ball swinging in cricket and why it happens.

Physics in Cricket Ball Swing

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Basically, there are 2 different things that make a ball swing in a certain direction. The first is the surface of the ball and the other is the correct pace of bowling. Ravindra Mehta, a scientist who explained the swing of the cricket ball using the concept of fluid mechanics. When the ball flies right through the air, a thin layer of air forms along the surface of the ball called the ‘boundary layer’.

This boundary layer does not attach to the surface of the incoming ball but acts around it and remains separate. The correct location of this point of separation determines the correct pressure of the ball. Here a pressure of air acts at a relatively late stage resulting in low pressure in that particular direction. Side force or swing will only develop if the pressure difference between the 2 sides of the ball remains constant. Moreover, the point of separation of the boundary layer is actually determined by the surface of the ball and the speed of the blow. Before going into more details on how to swing a cricket ball, let’s first know about the surface of the ball. This is where the concepts of simple flow and turbulent flow come into play.

When the match starts, the seam of the ball is shiny and smooth at both ends. However, after some time, one side of the ball becomes a bit rough. Therefore, the surface of the ball is different and the separation of the air boundary layer occurs in two different ways. While there is no air resistance on smooth surfaces, there is a disturbance on other rough surfaces. This is why the smooth layer has a straight i.e. uniform flow and the rough layer has a turbulent flow resulting in late separation. This difference in flow causes the wind speed to change in both directions and cause the ball to swing.

Connection between ball seam and swing bowling

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Fast bowlers use the seam of the ball intelligently to create swing in bowling. If you’re wondering how this happens, listen to it happen basically the same way as explained above. The seam of the ball is basically used as a rough surface and creates a flow which we call turbulent flow which causes the ball to swing. This is basically done by releasing the ball efficiently along the seam and that too at a certain angle to the initial flight line.

So, the ball will swing in the direction the seam is pointing. That is, if the ball is released with the seam angled towards the slip fielders, it will swing right away from the batsman. However, if the ball is released with the seam pointing towards fine leg, it will swing to the batsman’s right. In this case we call them outswingers and inswingers respectively.

A cricket ball can be swung like this even in the first over of a match when both sides of the ball are smooth and shiny. As the match goes on, the bowlers actually try to keep one side of the ball shiny. You may have seen some bowlers apply saliva or sweat on the ball and then rub it properly with their cloth. This is done so that one side of the ball is shiny and smooth. Although some people believe that the ball swings correctly because it loses some weight, this is definitely not true.

How does reverse swing work?

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So, now that you know how the ball swings and it’s important to keep one side of the ball shiny, do you think it’s not possible to swing after 30 overs when both sides of the ball are rough? OK, and this is where the ‘reverse swing’ technique comes into play. As the name suggests, in reverse swing the ball will roll in the smooth side instead of the rough side.

Bowlers’ efforts to keep a single side smooth results in a rough side and a super-rough side when the match is over 30 overs. Now it’s time for the reverse swing. In reverse swing, the bowler may bowl inswinger but will still swing away from the batsman.

This is because the force velocity actually transforms the air at both ends from a turbulent to a turbulent flow. This flow is propagated by the rough surface therefore, the turbulence is not able to hold the surface and hence there is an initial separation. Thus, the turbulent layer air on the relatively smooth side will be trapped a bit longer before it actually separates and so reverse swing occurs. It can be a tough challenge for the batsman as it is a tough ball to win.

Conclusion

After the above discussion we hope you now understand how the cricket ball swings. When it comes to swing bowling, the technique is definitely impeccable and creates a lot of challenges for the batsman to bat. If you enjoy reading the blog, do visit our official website for more interesting content like this.

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