Every four years, FIFA introduces a new official World Cup ball. A ton of science goes into the process -- and whether the players like it comes down to physics.
Designed by Adidas, the ball itself is not meant to make headlines. But over the last two Cups, that's exactly what's happened. In 2010, Brazilian striker Luis Fabiano described that World Cup's ball - the Jabulani - as "supernatural." Italian goalkeeper Gianluigi Buffon said, "It's trajectory is unpredictable."
The reason that balls seemed so erratic is that it was "knuckling" at different speeds than expected. Knuckling is when the ball wobbles in the air, following an unpredictable flight path. It's a tool for strikers, a menace for goalkeepers.
Traditionally, a typical soccer ball knuckles at about 30 miles per hour. This is slower than average kicking speeds, so it requires a bit of skill for the strikers to kick at precisely the right speed. But in 2006, it was knuckling at about 50mph, a speed more typical at the World Cup level. That meant the ball was knuckling much more often. In 2010, the speed for knuckling was even higher.
Leading into the 2014 World Cup in Brazil, Adidas addressed these issues with the new "Brazuca" ball. The 12th official World Cup ball designed by the company, it features six propeller-shaped polyurethane patches that are thermally-bonded together.
The 2010 Jabulani ball had eight panels. The 2006 ball had 14. Before that, the balls were made of 32 internally-stitched panels. By decreasing the number of panels, they decreased the seams, creating a smoother surface. This smoother surface allows it to travel at higher speeds before it started knuckling.
"The surface characteristics - the seams, seam length, how the seams shape the surface of the ball -- have a lot to do with how active the ball will be," Dr. Kim Blair told CBS News in a phone interview. Blair is a material scientist with Cooper Perkins in Boston. He was not involved in designing the Brazuca.
Researchers at the Centre for Sports Engineering Research at Sheffield Hallam University measured the seams of the Jabulani and the Brazuca, determining that the Jabulani's seams are about .48 mm deep compared to 1.56 mm for the Brazuca. The seams on the Brazuca stretch to 327 cm, compared to 203 cm on the Jabulani.
The ball went through a range of scientific tests to assure that it would complement the players' skills on the field, rather than adding a skill set all its own. "We do extensive flight path analysis and the results have shown constant and predictable paths, with deviations hardly recognizable," Matthias Mecking told the BBC. Mecking is Adidas's football director.
"We've come full circle," says NASA Ames Research Center scientists Ravi Mehta. "It's back to knuckling at about 30mph." He was not involved in the design but has tested the ball. Another important factor, he says, is the amount of friction between the ball and the player's boot.
The smoother 2006 and 2010 balls decreased this friction, making it harder for players to put spin on the ball. They had aerodynamic grooves and small ridges, but these were "not effective," says Mehta. The latest version, with its deeper and longer seams, fixes this issue. There are also small dimples on the surface to help decrease drag. These work in the same way as the dimples on a golf ball -- by disrupting airflow, they allow it to travel faster.
No matter how often the ball is changed, Blair pointed out, it will never keep every player happy. He recalls players complaining that the ball was "too light" in 2010. "It couldn't be," he said, because FIFA strictly regulates nearly every aspect of ball design, including weight. "The one thing that FIFA does not test for is aerodynamic performance," he said.
In the end, as with all elements of a game, it comes down to how the players adjust.
"All the players are playing with the same ball. They all get introduced to the ball at the same time," he said. "Some will be able to adapt their style quicker, some will evolve faster than others do."