NASA joins criticism of World Cup ball Jabulani | inside World Soccer


NASA joins criticism of World Cup ball Jabulani

Wednesday, July 7, 2010

Space agency NASA has become the latest to put the boot into the ­Jabulani after subjecting the infamous 2010 World Cup ball to a series of aerodynamic tests.

The Jabulani has been subjected to stinging criticism from players, coaches, pundits and journalists for its perceived flight trajectory, uncontrollable speed and unusual behaviour.

Spain goalkeeper Iker Casillas described the ball as "appalling" while Gianluigi Buffon, who guided Italy to the 2006 World Cup, went further by claiming that "it is very sad that a competition so important as the world championship will be played with such a horrible ball."

Others have likened the adidas manufactured product to a "supermarket" ball and its controversial performance has also been blamed for the lack of spectacular long-range goals, free kicks and the paucity of top-quality passes and through balls at the World Cup.

And analysis compiled by NASA’s Ames Investigation Centre experts, who specialise in the field of aerodynamics, revealed that the Jabulani becomes "unpredictable" at speeds over 44mph.

They also blamed the ball’s light weight of just 440 grams for the poor flight and lack of ­consistency, known as the "knuckle effect".


Rabi Mehta, an aerospace engineer at NASA, 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).

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