Thursday, August 06, 2009

The science of swing – clouds don’t help

I urge you all to read this article. It is a fascinating exposé of the modern myth of swing bowling. In essence, the idea that humidity effects movement is false.

A NASA scientist, after a series of exhaustive experiments, failed to prove a connection between atmospheric conditions and the extent of swing.

Rabindra Mehta, the aerodynamic expert in question, argues that there are many causes and methods of swinging the ball. In fact, there are three types of swing.

1. Normal swing.
Caused by turbulence in the airflows around the seam, reducing the pressure on one side, altering the trajectory. The age, lacquer and condition of the leather is irrelevant: it is the seam that singularly disrupts the air flow.

2. Reverse swing
Caused by roughness on one side of the ball, because of the poor condition of the leather. This leads to increased turbulence on one side, and the decreased of air pressure moves the ball towards the rough side.

3. Contrast swing
With seam position straight, the relative roughness of one side disrupts the airflow, deflecting the ball’s path. The direction depends ball speed.

Prevailing winds affect the extent of air turbulence. As does the condition of the pitch, soft, grassy pitches protect the seam and the shine of the ball. Abrasive pitches scuff it up and hard wickets depress the seam. The weather conditions are largely irrelevant.

The article suggests that overcast conditions only give a psychological advantage, such is the depth of the myth’s acceptance.

I suspect that as the softness of wickets protects the balls, then in the days of uncovered pitches, clouds and accompanying rain would give rise to conducive conditions indirectly by softening the pitch.

The strength of myths, like any ideas, is usually confirmed through years of repetition. Indeed, just below the Times’ article, is a piece about how England’s bowlers failed to capitalise on the “humid conditions” at Edgbaston.

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