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How all the top footballers can bend it like Beckham By Roger Highfield, Science Editor of Telegraph
Football legend has it that some players can kick a ball in an S-shaped trajectory, so long as they line up the valve and seams.
Now scientists using computers to simulate air flows have confirmed that a ball can snake its way into the goal in this method.
Some of the world's best goalkeepers have been beaten by balls that move to the left and the right, even though they have little or no spin applied to them.
Today, pioneering work at the University of Sheffield, in collaboration with Fluent Europe, has unravelled the mystery of such kicks. The research also suggests that the new Adidas Teamgeist 2006 Soccer Ball will move more predictably than ever.
The shape and surface of the ball with its stitches and seam patterns, as well as its initial orientation, is critical for these strange trajectories, according to studies by Dr Matt Carré's team at the university's Department of Mechanical Engineering.
Fifa regulations allow a deviation from perfect roundness of up to 1.5 per cent and the Sheffield research shows that a combination of the ball not being perfectly round and its initial orientation significantly affects the flight.
The work proves that a ball can suddenly swerve, dip or rise without any spin being applied, mostly due to the panel with the valve.
"A free kick by Ronaldo, of Manchester United, this season seems to show this phenomenon quite clearly much to the amazement of TV commentators," said Dr Keith Hanna, of Fluent.
Dr Carré said: "Any non-uniformity of design of soccer balls will have a dramatic effect on the side forces of the ball when there's little or no spin applied to it, and hence its swerve through the air. We believe that our findings go a long way to explain the phenomenon observed when some players kick the ball with little or no spin, yet get it to swerve in a seemingly erratic manner."
They studied and compared airflows around four balls, all with different panel designs, each having been used at different periods over 36 years, up to and including the new Adidas ball for the World Cup, the roundest ever.
Sarah Barber, a PhD student and Sheffield FC (ladies) player, with Dave Mann, the principal engineer at Fluent, used a 3D laser scanner to digitise the dimensions of each ball, including stitches and seam patterns.
They demonstrated that the shape, surface and asymmetry of the ball, as well as its initial orientation, had a profound effect on how the ball moved after being kicked. Strangely, the effects are more difficult to anticipate the less the ball spins, said Dr Carré. The side force varies according to the orientation of the ball relative to its flight, meaning that for a kick where the ball is slowly rotating, the side force could fluctuate, causing it to swerve.
This fluctuation repeats itself as the seam pattern on the ball rotates. In this way, it is possible for an S-bend to occur if the side force fluctuates from left to right during the trajectory.
Roger Highfield, Science Editor of Telegraph.
Posted on 15 Aug 2006 by coachgianni