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Ball speeds and forces

The movement of the soccer ball through the air is affected by the initial forces applied to it by the head or the foot, then while it is in the air, gravity and aerodynamic forces can cause it to curve. Putting rotation on the ball can cause it to bend in the air like a baseball curve ball. A free kick has been measured at speeds up to 70 mph speed with a spin of 600 rev/min. David Beckham famously uses spin imparted on the ball to curve a free-kick around a defensive wall and goalkeeper to score his goals. Calculations show that at 25 m from the goal and a velocity of 25 m/s, Beckham can swing the soccer ball 4.57 m from the straight path by using spin.

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2010 World Cup Ball

Throughout the 2010 World Cup there were complaints by payers about the ball in use - the Adidas-made "Jabulani" ball. The name Jabulani means "bringing joy to everyone", but it did not seem to bring joy to the goal keepers and strikers who claim it has erratic and unpredictable flight. A scientific analysis of the ball supported the players. Analysis concluded that the ball may simply have been too round to fly straight. Part of the problem may be also that the stitches of the Jabulani are internal, so the ball resembles a perfect sphere. Irregularities such as exposed seems on the surface of balls insure a more stable and controlled trajectory, and are what make possible spin in tennis or a curve ball pitch in baseball. Adidas countered the lack of stitches by designing the ball with 'grip n groove' texturing and claimed that it improves the stability of its flight and the players' grip when striking it - which was not supported by the results on the field.

See more about the World Cup Balls.

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