The mystery of the swinging ball in cricket has only recently been understood from a scientific perspective. Physicists have discovered some of the secrets that make a cricket ball swing in the air as it approaches the batsman. The air flow around the ball, the speed of delivery, the angle and height of the seam and even the weather contribute to making batting difficult and bowling — when the ball swings — an enjoyable experience.
The resistance of air molecules when a cricket ball passes through the air on its way to the batsman creates what Rabindra Mehta, a NASA scientist, calls “a boundary layer” around the ball’s surface. In the ESPN article “The Science of Swing Bowling,” he says that the “boundary layer cannot stay attached to the ball’s surface all the way around the ball and it tends to leave or ‘separate’ from the surface at some point … A side force or swing will only be generated if there is a pressure difference between the two sides of the ball.” The seam of a cricket ball, or the deliberate roughing up of one side and polishing of the other, creates the variation in air flow. This variation increases the likelihood of air flow separation on one side of the ball that causes the movement in the air.
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