Science of Cricket - Contrast Swing

This is the 3rd in a series of posts about swing in cricket. The terminology is introduced gradually, so it is recommneded that you read The Science of Conventional Swing and The Science of Reverse Swing first. This time, we will discuss contrast swing, which is often confused with proper reverse swing. Contrast swing is actually the most simple type of swing conceptually.

We will start with a diagram from Mehta again.
The first major difference you will notice is that the seam is pointed straight. This means that the only difference between the sides of the ball is the roughness. At conventional swing speeds only the boundary layer flow over the rough side will become turbulent, meaning that it will stay attached longer. This means that the pressure exerted on the smooth side will be greater and the ball will move towards the rough side, meaning the ball is moving 'reverse'.

At reverse swing speeds, both sides will transition to turbulence. If the rough side is exceedingly rough, this roughness may have a similar effect as the seam in reverse swing and weaken the boundary layer, causing earlier transition. I think however, that this type of swing would cause minimal ball deflection compared with slower contrast swing or either seamed swing types. Any movement that would occur would be towards the smooth side.

The seam is irrelevent to contrast swing and so this type of swing can be practised with a standard 1/2 taped tennis ball (not 1/2 a ball, 1/2 taped).

A note on speeds: For both slow contrast swing and conventional swing, there is not only an upper limit to the speed the ball is bowled at, but also a lower limit. Below a certain speed, neither side will transition to turbulence. So for you park bowlers out there, you may simply be bowling too slow to swing it. All these speeds mentioned will vary depending on atmospheric conditions, as explained in the post on reverse swing.

Next in the series is spin bowling 'drift'.

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