科学家眼中的世界杯足球

LINDA WERTHEIMER, HOST: With the World Cup underway, many of us are watching the drama on the field, but some scientists are keeping their eye on the ball. As NPR's Geoff Brumfiel reports, changes to the soccer ball used at the World Cup have made it the subject of controversy and intense research.

GEOFF BRUMFIEL, BYLINE: Is soccer ball is a soccer ball, right? Wrong.

JOHN ERIC GOFF: The rule book does not specify how many panels are on the ball or what the shape of the panels will be.

BRUMFIEL: John Eric Goff is a physicist at Lynchburg College in Virginia, who studies World Cup soccer balls. Traditional balls have 32 black-and-white panels, but in 2006, Adidas, which makes World Cup balls, started making balls with fewer panels. The ball for the 2010 World Cup in South Africa had just eight. Adidas said the new ball was more state-of-the-art - rounder. But it got off to a wobbly start.

GOFF: When the players would try to kick the ball straight - in other words, the ball would not have a lot of spin on it - there would be an erratic knuckling effect that would take place.

BRUMFIEL: A free kick by the Japanese striker Keisuke Honda was a prime example of how erratic the ball could be. The ball sailed up, and then suddenly swerved down past the Danish goalie.

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UNIDENTIFIED ANNOUNCER: What a strike from Keisuke Honda. That's probably the best free kick we've seen in the FIFA World Cup of 2010.

BRUMFIEL: Honda got the glory, but goalies were furious about the ball's uNPRedictability. One called it a supermarket soccer ball.

RABI MEHTA: Players really complain about the ball knuckling, and that's when I started looking at what the differences were.

BRUMFIEL: Rabi Mehta is an aerospace engineer at NASA's Ames Research Center in California. Ames is home to wind tunnels where researchers test everything from fighter jets to space probes to soccer balls.

MEHTA: In a way, it's not very complicated 'cause it is round. It's a sphere.

BRUMFIEL: But in another way, it is complicated. Because the change in the number of panels changed the seams between the panels, and that radically altered the ball's behavior. As air flows around a 2010 World Cup ball, it can snag on a seam. And at just the right speed, that seam acts as a rudder, causing the ball to shift direction suddenly.

MEHTA: It's basically an uNPRedictable, erratic flight path. And that, as you can imagine, can give a goalkeeper fits, really.

BRUMFIEL: Adidas has now changed the design again. In December, they unveiled the World Cup ball for Brazil in a promotional video. It's called The Brazuca, and this time the company appears to have learned their lesson. Mehta says the new ball has longer, deeper seams that keep it from swerving. He studied independent data from a Japanese wind tunnel. He's also been carefully watching kicks on TV.

MEHTA: I will be really surprised if players complain about this ball. I think this ball is behaving pretty well, just like the traditional soccer ball that they're used to.

BRUMFIEL: So after years of careful research, Adidas is producing a soccer ball that performs as well as a traditional soccer ball, which makes you wonder. Why did they change it at all? Adidas didn't respond to an interview request, but physicist John Eric Goff thinks he knows why.

GOFF: The Brazuca, right now, is selling for $160, $170. And Adidas can't get them out fast enough. Frankly, it just makes Adidas a ton of money every four years when they have a new ball that everybody wants to buy.

BRUMFIEL: But Goff and Mehta agree, you don't have to spend all that money for an aerodynamically state-of-the-art soccer ball. The old one you've got in the garage is just as good. Jeff Brumfiel, NPR News.

WERTHEIMER: This is NPR News.