It’s Not Rocket Science, Just a Soccer Ball

The World Cup ball leaves a trail of criticism, and complex separated smoke patterns, in its wake


It's been described as a nightmare for goalkeepers. England's coach called it the worst soccer ball he has ever seen. And still others say they're doing what players do when a new ball is introduced -- getting used to it.

However you feel about the official ball of the 2010 World Cup, called the Jabulani, we can all agree on one thing -- it's a good reason to fire up the Caltech wind tunnel.

On Wednesday, people who know what it takes to send a rocket to outer space conducted tests on the ball. The tests were designed to show the complexity of air flow over the soccer ball. Smoke was introduced to the wind tunnel, allowing scientists to watch it stream over the ball.

"What you're looking for is where the flow leaves the surface of the ball," Bevelry McKeon, assistant professor of aeronautics, said as a colleague secured a soccer ball in the tunnel. "If you look at the front, you'll see the smoke follows the curvature very well. In the rear half, the smoke separates and leaves the ball and forms a very complex wake."

Watch the video above to see for yourself.

"The size of that wake, which is linked to where that flow separates, dictates the drag that acts on the ball. If that wake is not symmetrical, that will impart a side force to the ball," said McKeon.

The big difference with this World Cup's ball involves the manufacturing process, especially how its eight panels are joined. 

"When you look at the older ball, you can see that the panels are the equivalent of stitched together," McKeon said. "In the new ball, it's much more round and there's a more controlled manufacturing process. One of the claims of Adidas is it's a much rounder, truer ball."

Adidas boss Herbert Hainer defended his firm's ball earlier this week. At a news conference Monday, Hainer said the ball  is "rounder than any ball we have ever made, more aerodynamic and goes faster."

That might be true, but England coach Fabio Capello described it as the worst he had ever seen. And that's exactly the way many England fans described his goalkeeper's performance the group stage 1-1 tie with United States.

In the end, McKeon said the admittedly non-comprehensive tests suggest that when it's kicked, the ball can switch from smooth to turbulent airflow and back. She said that it might appear to the goalkeeper (any goalkeeper, not just Robert Green) that the ball might be changing trajectory.

McKeon, who is English, did not go so far as to blame the ball for the goalkeeping blunder. In fact, she said the ball's unpredictable behavior can add to the excitement.

"It's much more exciting because you're just not used to the way this ball behaves," McKeon added. "Something you think is nowhere near the goal may go in. Plays that look dead may not be dead. We don't intuitively understand what the trajectory of these news balls will be, yet."

Professors of aeronautics aren't the only ones who have done their research. South Korea's Lee Chung-Soo and Park Chu-Young both scored on free-kicks in their match against Nigeria.

"Compared to other balls, if you kick it too hard, then 80 to 90 per cent of the time it seems to go up in the air, too high," said South Korea coach Huh Jung-Moo. "So we trained so that it would be kicked lightly, without hitting it too hard. I think we adapted well to the ball."

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