NASA: World Cup soccer ball still needs work

NASA engineers weigh in on the controversial design of Jabulani, the official soccer ball of the World Cup.

Adidas, which designed Jabulani (named after the Zulu word for "celebration"), has resurfaced the soccer ball and cut down the number of exterior panels after players at the 2006 World Cup and again at this year's cup complained that the ball's movement was unpredictable and made goalies' jobs harder.

Jabulani now has 8 exterior panels, down from 14 and before that 32. Adidas has also added what it calls "aerodynamic grooves" to the ball's surface and has fused the panels, which are 3-D and "spherically molded," to make Jabulani "perfectly round and even more accurate than ever before."

Not so, says Rabi Mehta, an aerospace engineer at NASA Ames in Mountain View:

"It's quite obvious. You're seeing a knuckle-ball effect," [Mehta said in a statement released by NASA.] He explained that when a relatively smooth ball with seams flies through the air without much spin, the air close to the surface is affected by the seams, producing an asymmetric flow. This asymmetry creates side forces that can suddenly push the ball in one direction and cause volatile swerves and swoops.

From his research on tennis and cricket balls in wind tunnels, Mehta believes that the Jabulani ball will tend to knuckle at 45 to 50 mph, which coincides with the speed of the ball during free-kick around the goal area. Another point made by Mehta, is that a lot of the stadiums for the World Cup are located at high altitude (Johannesburg is at 5,500 feet) and this will affect the ball aerodynamics as well, since the air density is lower. At this high altitude, the ball will tend to fly faster (less drag) and swerve less (less lift).

Mehta demonstrated his theory by inviting a player from the local pro soccer team, defender Stephen Beitashour of the San Jose Earthquakes, to kick Jabulani in front of a group of students who are learning about aerodynamics. Beitashour wasn't impressed either, according to NASA.

"The new ball moves a lot," Beitashour told NASA. "When I hit it smack straight in the middle with force, it changes direction in the air. It's harder to track, so players will have to focus more."

The coach of the Portuguese national team claimed Monday that his players are happy with Jabulani after they beat North Korea 7-0 in the pouring rain. Maybe the fact that Jabulani got soaked the pitch was wet made the ball heavier and therefore easier to control, although North Korea's problems with defense, which fell apart in the second half, went well beyond the ball.

Adidas defends Jabulani too -- it's selling the balls for $150 each. But let's see how well Portugal likes Jabulani on Friday after they play Brazil!

UPDATE: Here's a video from NASA that shows how the ball travels when it's kicked. (Speed through -- the ball demo is near the end).

Related on Smart Planet:

The science behind the World Cup 2010 soccer ball, Adidas Jabulani

Goal! Electric soccer balls tap the energy of the World Cup game

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