The design of the modern football makes it more susceptible to chaotic behaviour, soccer science expert Dr Ken Brady told the BA Festival of Science on Saturday. 'When the ball leaves Cristiano Ronaldo’s foot, we’re talking about the physics of chaos.'

Ronaldo kicks so-called knuckleballs: ones with very little spin. They weave unpredictably through the air, and neither Ronaldo nor the goalkeeper can foresee their flight. They present impossible targets for goalkeepers.

'Football is a game of developed skills,' said Brady. 'Why should we make goalkeepers look like fools?'

Dr Brady is from the Sport & Exercise Science group in the University of Bath’s School for Health.

Adidas is currently designing the ball for the 2010 World Cup. 'There’s a tremendous amount of technology that goes into that,' said Brady, 'and in every respect that technology produces a better product. You could not kick a more predictable object round the football pitch - with one exception. Aerodynamic performance is the fly in the ointment.'

'It’s time for FIFA to act,' he said. 'They control the ball size, its weight, sphericity, recoil in a bounce and water absorption – but not its aerodynamic performance.'

Dr Brady explained how David Beckham produces goals from free kicks.

'The striker has to move the ball over the defensive wall, swerve it and bring it down in time for it to score,' said Brady. 'What he’s got to do is to move the ball through extremely narrow limits at the location of the defensive wall.'

The easiest free kick is taken centrally to the goal. 'If the striker is 25 metres from the goal line, and kicks the ball at 28 metres per second, he has to kick it through a "letterbox" whose "slot" is only one ball high and six balls wide,' said Dr Bray.

'As the striker gets closer to the goal line, or further to the side, the slot shrinks.'

In a technique first used by Brazilian midfielder Waldir Pereira (Didi) in the 1950s, Beckham kicks with sidespin so that the ball spins like a top about a vertical axis and deflects sidways. He adds topspin as well, which makes the ball both swerve and dip.

'The kicking action must be very precise,' said Bray. 'A few degrees of difference to the side, a few degrees of difference in elevation, a metre a second or so differentiation of speed, and it’s a waste.'

Dr Bray alluded to the complicated mathematics behind discovering the exact effect of spin and aerodynamic drag on the trajectory of ball. However, he does not think that coaches should present the science to their top players.

'Elite free kickers do this intuitively and by assiduous practice. I’ve heard it said that David Beckham is a master of aerodynamics, but he and the best of them don’t need to be. They do what they do because they’re supreme athletes.'

Dr Bray’s new book, How to score – science and the beautiful game, is published by Granta.

Read the coverage in the Sunday Telegraph.