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Uploaded on Jul 2, 2010
Rabi Mehta, an aerospace engineer at NASA Ames in Mountain View said: "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).