The third Test Match between England and the West Indies starts at Edgbaston today in wet and humid weather. If rain does not completely stop play, the swing bowlers should be pleased. According to a widely held belief, muggy conditions are supposed to help bowlers make the ball swing more, swerving towards or away from a batsman, although exactly why has long been contended. But a recent study debunks the extra swing in humid weather as a myth. Scientists at Sheffield Hallam University and the University of Auckland, New Zealand, tested the claim using laser scanners in an artificial weather chamber under varying levels of humidity. Using balls of different wear to simulate match conditions, they could find no link between the moisture in the air and the swing of the ball.
There is good science, though, to a bowler rubbing a cricket ball on one side, leaving the other side smooth. As air rushes past the scuffed side of the ball it becomes more turbulent than the smooth half, leading to an imbalance in pressure, and making the path of the ball bend sideways.
The scientists made a particularly surprising discovery when they interviewed various world-class cricketers on this topic, including Andrew Flintoff. Contrary to expectations, these players dismissed the importance of humidity, but they were convinced that the ball swings more on cloudy days. Although the level of humidity on cloudy days tends to be higher, they all believed that humidity is not the key factor.
The researchers suggest that there is good science for this, because cloudy conditions can give calmer air that helps to swing the ball. “Cloud cover can lead to a general stillness in the air, and low levels of air turbulence are good for swing bowling as the bowler will be more able to create an asymmetry of air flow around the ball,” the scientists wrote. On the other hand, sunny conditions heat the ground, hot air rises up and creates more turbulence, upsetting the imbalance of pressure across the ball. The study is published in the Procedia Engineering journal.