adminIT is one of the stars of the World Cup – the paintbrush with which the world’s greatest footballing maestros must create their art.
But is it up to the task? The Brazuca, the official ball of Brazil 2014, is the 12th ball created by Adidas for the World Cup. The company came under fire four years ago for the Jabulani, the official ball at the 2010 competition in South Africa, which was heavily criticised. “It’s trajectory is unpredictable,” claimed Italian goalkeeper Gianluigi Buffon while Brazilian striker Luis Fabiano branded it “supernatural”.
Adidas claims the Brazuca has improved touch and accuracy.
“We do extensive flight path analysis and the results have shown constant and predictable paths, with deviations hardly recognisable,” Adidas’s football director Matthias Mecking told the BBC.
Experts in aerodynamics interviewed by the BBC outline three factors that are expected to influence how the official ball of Brazil 2014 will behave.
“The most important thing on the soccer ball is how much roughness you have,” explained Dr Rabi Mehta, branch chief at the US space agency’s (Nasa) Ames Research Centre in California, and an aerodynamics expert. The amount of roughness, he explains, “dictates what the critical speed is going to be at which you get maximum ‘knuckling’ of the ball”.
He tested the Jabulani in a wind tunnel and has been looking at the Brazuca. The so called “knuckling effect” occurs when the ball does not spin or spins very little.
Dr Mehta explains that when a relatively smooth ball with seams flies through the air without much spin, the air close to the surface is affected by the seams, producing an asymmetric flow. This asymmetry creates forces that can suddenly knock the ball, causing volatile swoops.
But “when the ball is spinning you get the Magnus effect that makes the ball curve”, he explains.
“It’s spin-induced side force. So when you see these banana kicks around the wall – for the free kicks like Bend It Like Beckham . . . that is exactly the Magnus effect.”
It is the knuckling effect and the smoother surface of the Jabulani, compared to the Brazuca, that explains its unpredictability, according to the Nasa engineer.
Older, traditional balls that have been internally stitched with the standard 32 panels “knuckled” at around 48 km/h (30 mph).
“The smoother you make the ball, the higher the speed at which it knuckles,” says Dr Mehta.
“In essence what happened in my opinion is that with the traditional ball, the critical speed at which you got maximum knuckling was lower than the typical kicking speed in World Cup soccer.
“By making the ball smoother, that critical speed went up and happened to coincide with the typical kicking speeds, about 50, 55 mph (80, 88 km/h), especially in free kick situations.”
By making this year’s ball rougher, according to Dr Mehta, “we’re back to square one”.
The texture of the Brazuca is rougher. “They have what I would call tiny little pimples, which also would help in terms of the aerodynamics,” says Dr Mehta.
“If you compare this to the Teamgeist (the official ball at the 2006 World Cup in Germany), the areas apart from the seams were very smooth. The rougher texture would also help solve other issues, like when you kick the ball there is more friction between the boot and the ball.”
But the major factor influencing the roughness is the geometry of the ball’s seams.
“Seams are important because they determine to a large extent the roughness of the ball,” Dr Mehta told the BBC.
The Brazuca has six thermally bonded propeller-shaped panels, less than the eight of the Jabulani, the 14 of the Teamgeist or the 32 of traditional footballs. Adidas says the new seam geometry will give the ball aerodynamic accuracy and a stable flight.
Fewer panels could actually make the ball smoother, but new ball’s roughness is increased in other ways, says Dr Simon Choppin, a research fellow at the Centre for Sports Engineering Research at Sheffield Hallam University, who has measured the seams of the Brazuca. – Online.
Online Reporter