The science behind the 2014 ball
In the previous football World Cup the ball itself played a key role because of its spectacular features. History is not likely to repeat itself this year, since the 2014 ball has been designed to give it a calm and predictable trajectory through the air, according to KTH researcher Fredrik Lundell.
How far the football travels through the air depends not only on how hard it is kicked. The ball’s design – especially the finish – is crucial.
The 2014 World Cup ball is made up of six flower-shaped fields. And in that surface lies the secret to how it will behave on the football fields in Brazil during the next few weeks, says Lundell, a researcher in fluid mechanics.
“It is a much more stable version than its predecessors. I think the players will be very happy with the path of the ball,” he says.
Lundell says that ball manufacturers resort to increasingly sophisticated methods to develop their products before the big tournaments. At the last World Cup, researchers at Loughborough University in England sought to develop a ball with better aerodynamics than ever.
The result – named “Jabulani” – had features that no one had seen before. Under free kicks, the ball wobbled sharply. The spectacular trajectories aroused protests, not least among goal tenders who could not predict where the ball would go.
This year's ball has also attracted the interest of the scientific community. An article in the journal Scientific Reports compares the ball's flight characteristics with those of recent decades’ predecessors. Lundell says that the creators put the ball – named “Brazuca” – through lot of tests with kicking robots and in wind tunnels to get it to behave like a normal, traditional football.
“One may ask, ‘What is the point?’ But there are of course major market values in developing a new ball for each championship. The conclusion this time is that the manufacturers seem to think that football works best when you use a ball with pretty standard features.
A ball wobbling in flight is not something you can negotiate away, it is a fundamental fluid mechanical phenomenon. The question is to what extent and at what speeds this occurs. In the case of Brazuca, the ball wobbles less at high speed, he says.
Small differences have an impact
The explanation is the elongated, multiple seams that connect the flower-shaped fields. The more seams, the earlier in flight turbulent air currents are generated on the surface of the ball. And those chaotic air currents are what cause it to flutter and wobble.
The laws of fluid mechanics also ensure that Brazuca gets a relatively calmer release with hard shots. It wobbles less than the last World Cup ball at typical football speeds. This happens because the air flow no longer follows the ball's surface in the same way.
“When you hold a ball, it's hard to imagine that it would have such different characteristics as shown in laboratory tests. It is fascinating that such subtle differences can affect the path of the ball,” Lundell says.
Which team will Lundell be cheering for in the World Cup?
“Probably Brazil, which feels like the only option when Sweden is not in it. When the semifinals are closer, I will certainly be looking at several matches, but I have not planned my holiday around the World Cup.”