Every four years, there is a new World Cup ball, and players have to adapt to its new behaviour due to changes on its aerodynamic properties. In 2010, the ball was called Jabulani -- known for its sometimes unpredictable moves. Has the new ball -- Brazuca -- solved these problems?
NASA has the answer:
The previous World Cup ball, the Jabulani, was described as sometimes demonstrating "supernatural" movements [...] when kicked with little or no spin, the ball "knuckled," giving strikers a greater chance of scoring. Knuckling occurs when, at zero or near-zero spin, the seams of the ball channel airflow in an unusual and erratic manner making its trajectory unpredictable.
At the same time, however, the lack of precision affected the entire game, so players generally hated it. According to NASA, Adidas "worked with hundreds of players to develop the Brazuca football" to solve this "supernatural" behaviour -- "a traditional football has 32 panels, the Jabulani has eight panels and the Brazuca has only six."
Did the new design work?
According to Dr Rabi Mehta, at NASA Ames Research Center, the answer is yes:
"The players should be happier with the new ball," predicted Mehta. "It is more stable in flight and will handle more like a traditional 32-panel ball."
Their aerodynamics tests show that the Brazuca's surface and panelling modifications are responsible for this improvement:
Despite having fewer panels, the finger-like panels on the Brazuca increase the seam length, compared to previous World Cup balls. The seams are also deeper than those of the Jabulani and the panels are covered with tiny bumps; all of these factors influence the ball's aerodynamics.
Dr Mehta says that this new roughness and panel configuration greatly affects the handling of the ball: "There is a thin layer of air that forms near the ball's surface called the boundary layer and it is the state and behaviour of that layer that is critical to the performance of the ball. The materials used, the ball's surface roughness and its distribution determines its aerodynamics."
The test results
Working at the Fluid Mechanics Laboratory at NASA Ames Research Center, Dr Mehta tested the ball in a wind tunnel and a 17-inch water channel, "which uses florescent dye dispensed into the fluid flow under black lights".
According to NASA, their tests "shows that the speed of greatest knuckling for a traditional ball is around 30 miles per hour (50km/h). This is well below the typical kicking speed of a World Cup-calibre player, which is about 50 to 55 mph (80km/h to 90km/h)." The Jabulani experienced knuckling at 50 mph because its smoothness, which is what drove players mad.
The Brazuca's knuckling speed is just 50km/h, so the players will have a lot more control.