The soccer ball created for the 2014 World Cup has a jazzy look and name: Brazuca. But despite its flamboyant style, it will fly more accurately than those designed for previous tournaments, scientists have found.
The Brazuca is destined to roll across televisions screens around the globe in the quadrennial clash of soccer titans that kicks off in Brazil on June 12.
Novel ball designs have become a regular part of World Cup marketing strategy in recent years. The Barzuca, created and manufactured by Adidas, retails for a tidy $150. But a change in ball design can also mean a change in performance, which in turn can affect the nature of the game.
So far, the Brazuca has been something of an unknown quantity at world level competition. Now a detailed study of soccer ball aerodynamics suggests that players will be able to kick and pass the Brazuca with greater speed and accuracy than they did with the balls that were used in 2006 and 2010 World Cup matches.
“Brazuca is more stable than the other balls,” said Sungchan Hong, a researcher at the Institute of Health and Sport Science at the University of Tsukuba in Japan and co-author of the study published today in the journal Scientific Reports.
Using a combination of wind tunnel tests and experiments that involved repeatedly lofting soccer balls with a mechanical kick-bot, the researchers showed how the shape and orientation of a soccer ball’s surface elements or panels can have a significant effect on trajectory. The difference can change where a ball ends up by as much as two metres, a huge amount in competitive play.
“This is a remarkable study. It shows that these balls are very different from each other,” said Stephen Morris, a physicist at the University of Toronto whose research includes the type of non-linear effects that come into play around the irregular surface features of a flying soccer ball.
Understanding exactly what happens around the surface irregularities of a ball in flight is no easy matter said Dr. Morris, who was not involved in the Japanese study. “But the seams are the key thing.”
A conventional soccer ball, with its iconic black-and-white pattern of pentagons and hexagons (32 panels in all) has a large number of short seams.
In contrast, the Brazuca ball is covered with 6 interlocking panels that are wrapped around the ball rather like splayed banana peels, creating a distinctive pattern of long, curvy seams.
For any design, the overall effect of the seams is to change the way air flows around the ball during flight. Certain factors can lower the critical speed at which the air flow suddenly changes and the ball can travel more easily with less drag. This so-called “drag crisis” occurs at a much higher speed when there is no surface roughness on a ball, so perfectly spherical balls do not tend to move as easily or travel as far. Like the dimples on a golf ball or the fuzz on a tennis ball, the surface effects created by the seams of a soccer ball help bring on the drag crisis at a lower speed.
For the 2006 World Cup, Adidas introduced a smoother, 14-panel ball design known as the Teamgeist, which seemed to alter the onset of the drag crisis and change the performance of the ball in unexpected ways. Players noticed the difference. The 2010 ball, an 8-panel design called the Jabulani, was meant to be an improvement. It wasn’t.
“If anything it got a little worse, “ said Rabindra Mehta, Chief of the Experimental Aero-Physics Branch at NASA’s Ames Research Center in California. “There were a lot of complaints.”
The new study shows that the Jabulani pushes the drag crisis up to a substantially higher speed compared to a conventional soccer ball, more like the speed of a typical hard kick. This leads to a curious side effect: Because of the pattern of seams on the Jabuanli, the airflow is more irregular at the drag crisis speed than it would be for other ball designs. When the ball is not spinning or spinning very slowly, this can lead to sideways forces that change the trajectory of the ball in unpredictable ways — an effect that is similar to the knuckleball pitch in baseball.
In soccer, some strikers specialize in trying to find just the right speed at which the knuckleball effect will appear, and so confound goalkeepers. But when the Jabulani arrived, suddenly the knuckleball effect became all too common.
“Anybody could strike the ball and it would move like that,” said Jordan Harvey a defensive player with the Vancouver Whitecaps Football Club.
Now playing in his ninth season, Mr. Harvey has taken a shine to the Brazuca ball, which was introduced in league play in North America earlier this spring.
“It strikes more true. It feels like it’s going where you want it go,” he said.
The Japanese study shows why. While the Brazuca has many fewer panels, the total length, depth and arrangement of its seams means that it performs more like an old-fashioned 32-panel ball and so flies more predictably. It also keeps the drag crisis at a low speed, yielding faster, straighter shots overall.
The study also found that both Teamgeist and Jabulani style balls behave quite differently depending on how their panels and seams happen to be positioned in flight. The Brazuca ball, like the conventional soccer ball, behaves similarly no matter what its orientation.
“It doesn’t look like a traditional ball, but aerodynamically it is,” said Dr. Mehta.
That bodes well for players and for fans said Dr. Hong, who said he personally prefers the Brazuca’s performance and hopes to improve the game with his research.
“Brazuca is faster than Jabulani in the middle speed range,” he said. “So I think that fast passes will be seen in [World Cup] games and this may be advantageous” to teams who play in that style.
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