The UK engineering department behind this year’s World Cup football is defending itself against criticisms from players that its hi-tech design produces unpredictable movements in the air.
A team led by Andy Harland at Loughborough University’s Sports Technology Institute designed the new Adidas ’Jabulani’ ball, which is constructed with eight spherical panels bonded together without stitches.
While not personally involved with the Jabulani project, institute director Mike Caine said Harland and his colleagues are surprised by the number of complaints they have read in the media about the ball, which is hyped as the ‘most perfectly round’ design ever created.
It is has gone so far that England manager Fabio Capello has reportedly claimed the ball’s erratic movements led to goalkeeper Robert Green’s error that granted the USA a goal in last weekend’s match.
We suspect the players are witnessing the effects of playing at high altitude
Prof Mike Caine, Loughborough Sports Technology Insititute
A number of players have insisted the new ball is too light and this is what makes its movements through the air more unstable. Caine said this cannot be true because the mass of the ball is 380 grams, which is the same as previous tournaments and within regulation, but there could be a scientific explanation behind the players claims.
‘We suspect the players are witnessing the effects of playing at high altitude,’ he said, referring to the notion that half the stadiums hosting games for this year’s World Cup in South Africa are located in high-altitude cities.
For instance, the England-USA match in Rustenburg was played at an altitude of 1,500m.
Caine said, ‘I think many of the observations can be explained by the effects of altitude rather than the ball per se. The ball will travel further. It will travel faster. It’s the basic physics that the air is thinner and the resistance to any projectile is less so the flight path of the ball will be different at high altitude.
‘It’s not surprising players feel a little bit disoriented with the flight of the ball when they’re playing at high altitude particularly when they don’t experience that on a regular basis.’
The effects of altitude aside, some sports engineers maintain the ball’s unusual movements can still be chalked up to its smooth stitchless design. According to wind tunnel tests conducted by Kazuya Seo of Yamagata University in Japan, when the ball is kicked and achieves flight of more than 45mph, Jabulani feels less drag and keeps it speed longer than previous tournament balls. This means it actually flies a few metres farther.
Seo’s research, which was supported by sports equipment manufacturer Molten USA, found that at slower speeds the ball’s aerodynamic behaviour begins to resemble more of a smooth sphere. His findings, which can be viewed in the attached file, show that when in flight the smoothness of the ball creates a horeshoe vortex in its wake. This vortex rotates on the wind direction irregularly and causes forces on Jabulani to fluctuate more than forces would fluctuate on traditional balls. These fluctuations could cause the ball to bend in unpredictable ways.
Caine said the Loughborough engineering team reject there is anything irregular about the aerodynamic properties about the ball and have proven this in their own wind tunnel tests at the university. The team took into consideration the effects increased smoothness could have on flight stability, he said, and therefore developed a patented technology for adding grooves into the panels of the ball. ‘The grooves are effectively there to enhance the dynamic stability of the ball in flight,’ he said.
Even though the technical innovations behind Jabulani have caused controversy, it is likely that enhancements on ball design will continue in the future.
As Gordon Taylor, chief executive of the Professional Footballers Association, put it, ’There has often been similar controversy as a new ball is introduced for every World Cup and this is equally challenging for the manufacturers.
’I don’t know if we can blame the ball for the mistake by our goalkeeper or even by Algeria’s goalkeeper but it is a fact that, as the ball’s become lighter and smoother, their trajectory is becoming more difficult for goalkeepers to cope with but then perhaps that is the objective.’