Why do bowlers rub the ball before bowling in a cricket match? Why do bowlers rub the ball before bowling in a cricket match? What is the science behind it? Is it because of friction?
 A: Your answer : The bowlers and fielders rub the ball to make the ball smooth and shiny on one side and leave it rough on the other side. To generate reverse swing.
There is a lot of science behind swinging the ball. The ball gets reverse swing when it is quite old and you see not only the bowlers but the fielders as well rubbing the ball before every delivery. What they are doing is preparing the ball for reverse swinging. before that one must understand how the ball swings.


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*conventional Swing: when the ball is new, it is shiny on both sides of the seam. when a bowler bowls the ball, the surface of the ball experiences air flowing through it. The seam acts as the separator. when both surfaces are equally exposed to the air (seam up delivery), the ball goes without deviation in the air and then swings once it pitches on the surface, due to the uneven seam.
Inswing/Outswing: But when one of the surface is exposed more to the air, the seam acting as the separator, one surface experiences more push from the air and swings in the direction opposite to the surface exposed. In this way you get your conventional inswing and outswing deliveries.


After some time the ball starts to get rough and the ball becomes soft and rough and eventually stops swinging in the air. It is now when the reverse swing will start. The fielding team has prepared the ball for reverse swing by rubbing one of the surfaces constantly after every delivery so that one of the side is still smooth and shiny while the other surface is rough. 
Now when the bowler bowls, the ball has one of the surface shiny and smooth and the other side is rough, the smooth surface passes through the air more smoothly and faster(like laminar), while the rough surfaces does not passes through the air so smoothly(like turbulent flow). As the shiny surface allows the air to pass quicker, and rough surface has friction, it experiences a constant push from the air (as the air is passing through a rough surface) and the ball swings towards the shiny side. this is called reverse swing. 
Your answer : The bowlers and fielders rub the ball to make the ball smooth and shiny on one side and leave it rough on the other side. 
