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Tue April 22, 2014
A Knuckleball No More: World Cup Soccer Ball Gets A Redesign
Originally published on Wed April 30, 2014 11:12 am
John Eric Goff, the chair of the physics department at Lynchburg College, explains the science of the 2014 World Cup soccer ball. The Adidas Brazuca is expected to perform better than the version used in South Africa in 2010.
AUDIE CORNISH, HOST:
From NPR News, this is ALL THINGS CONSIDERED. I'm Audie Cornish.
MELISSA BLOCK, HOST:
And I'm Melissa Block.
If you think a soccer ball is just a soccer ball, think again. We're going to kick around the Brazuca. It's the official match ball of the 2014 FIFA World Cup. It's made by Adidas. It took years of development and testing to get it ready, and FIFA officials can only hope it avoids the scorn heaped on the much-maligned and erratic 2010 World Cup ball, the Jabulani. Lynchburg College physicist John Eric Goff has been studying aerodynamic wind tunnel tests of the new Brazuca ball.
JOHN ERIC GOFF: I started analyzing the data and creating some trajectory models. And we now have a pretty good understanding of what the Brazuca ball is going to do, and it looks a lot better than the Jabulani.
BLOCK: Yeah. Well, let's go back just a bit to that 2010 World Cup ball, the Jabulani. Goalkeepers at the time, said this: It's dreadful, like a beach ball goes all over the place, a catastrophe. They hated it. So what was going on aerodynamically with that ball that now that they're hoping they fixed?
GOFF: So a lot of us probably kicked around a soccer ball that had 32 panels on it, kind of the traditional, the 20 hexagons, the 12 pentagons. The Jabulani ball only had 8 panels. It was intentionally textured by Adidas. And what happened was they didn't count on the fact that the drag crisis - where you have this drop in the drag coefficient on the ball - took place at speed scene on the soccer pitch all the time, these intermediate speeds of between about 30 and 55 miles an hour was this region where you're going to get a knuckling effect on the Jabalani ball. And that's been corrected with the Brazuca ball.
BLOCK: And when you say knuckling effect, what are you talking about?
GOFF: So if a ball is kicked with very little spin, think of a knuckleball in baseball, you can get air flowing over part of the ball where it's rougher than another part of the ball on, say, the opposite side where it's smooth. Think of the seams on a baseball versus the smooth part. That leads to different float characters around ball, and you can get sideways forces. And that's what we refer to as the knuckle effect.
BLOCK: OK, so that's the - that's what was going on with the Jabulani, those wacky, erratic flight patterns. So now you've tested the new ball, the 2014 ball, what did you find? Have they fixed it?
GOFF: So the Brazuca now has the drag crisis at a much lower speed, meaning the intermediate kicks - the really strong, the powerful kicks - are all going to be past this drug drag crisis. So I would not anticipate the kind of knuckling effects that you would see back in 2010.
BLOCK: OK. So at those lower speeds, lower kick speeds that you're talking about, that's where you might see a problem in this World Cup.
GOFF: That's right. And we also had the ball oriented at different locations to check the uniformity of the ball. And the reason this ball is so much better is it has a seam length that's about 68 percent longer than the Jabulani. It makes for a much more uniform ball. You see the same aerodynamics as you turn the ball. Jabulani, you could turn it 90 degrees and see a very different drag profile.
BLOCK: So I'm thinking that this summer if you watch the World Cup, you're going to be paying really close attention to the spin of that ball and this drag crisis that you're talking about.
GOFF: Absolutely. Especially the kicks with very little spin, I'm going to be interested to see if there's much knuckling at all as they start spinning. Then we get these great banana kicks that you see from the corners and nice curves from free kicks.
BLOCK: Professor Goff, thanks so much for talking to us about the World Cup Brazuca ball. Appreciate it.
GOFF: It was a pleasure speaking to you, Melissa.
BLOCK: That's John Eric Goff. He is professor of physics at Lynchburg College and author of the book "Gold Medal Physics: The Science of Sports." Transcript provided by NPR, Copyright NPR.