Research in NASA wind tunnels revealed that the official ball of the previous World Cup, which was smoother, was unexpected and precisely the roughness that was deliberately added to the current ball allows the players to control it and the goalkeepers to predict where it will go
At the same time as the opening whistle (fThe opening kick was given by a disabled person who used robotic legs) of the 2014 FIFA World Cup, NASA also decided to join the World Cup celebration. Among the fans are also engineers at NASA who used the agency's wind tunnels (which is known to be the Aeronautics and Space Agency, this time with the emphasis on the first A), to try out Adidas' new ball, the official ball of the World Cup known as the Brazuca.
Although NASA is not in the business of designing and testing soccer balls, the tournament gave its personnel an opportunity to explain the concept of aerodynamics to students and other citizens who are less familiar with the basic physics laws of aerodynamics.
"The sport provides a good opportunity to present the field of aerodynamics to the next generation of researchers by illustrating the connection between the two." says Ravi Mehta, director of the Experimental Aerophysics Division at NASA's Ames Research Center at Moft Field, California.
Aerodynamics is the field that studies how air and fluids, collectively known as "fluids" flow around objects. Engineers at Ames, a world-leading research center in basic aerodynamics research, are generating a deep understanding of how fluids flow around simple three-dimensional objects such as cylinders and spheres. The knowledge allows engineers to predict how even small changes in these basic configurations will affect flow patterns.
The former soccer World Cup ball, known as Jabulani is sometimes described as having "supernatural" movements. He was also loved by strikers so hated by goalkeepers because when kicked with little or no spin, the ball started to accelerate and this gave the striker a greater chance of scoring. Acceleration occurs when in a state of little or no spin, it appears to cut through the air randomly and therefore its trajectory is unpredictable.
Dr. Mehta and Christina Ngo watch a test of a 32-sided football in a 17-inch water channel. The flow patterns are visible thanks to the use of glowing lighting and 'black light'.
Taking full advantage of the characteristics of the ball's flight, in order to shoot them, is nothing new in sports. In baseball, the only difference between different types of hits is the way the ball spins affected by the bumps on it. In football there are no external appendages other than the seams connecting the ribs but there are many of them.
To deal with the inability to predict the flight of the jabulani ball, Adidas, with the help of hundreds of players, developed the brazoca ball, traditional soccer has 32 ribs, the jabulani had eight and the brazuca has only six.
Although it has fewer ribs, the brazoca's toe-like ribs increase the length of the seams compared to previous official World Cup footballs. The seams also appear to be deeper than those of the Jabulani and the ribs are full of small bumps, factors designed to affect the aerodynamics of the ball.
What seems logical about air moving around a simple sphere is not entirely true. The air flow around a ball is not smooth, a significant amount of drag is created behind the bone. An example of this can be seen on a golf course when a golf ball stops at a shorter distance than a 'wounded' ball. The bumps on the surface of the ball stir up the air and create an area of low air pressure behind the ball, thus reducing friction, and therefore also increasing the distance the ball reaches.
A thin layer of air forms near the surface of the ball called the 'boundary layer'. Its shape and position affect the performance of the ball." says Mehta. "The material used, the surface hardness of the ball and the distribution of formations on the surface affect the aerodynamics."
All of these things affect the roughness of the ball and will help to reduce the unpredictable behavior of the average kick speeds in the soccer world cup.
In a 2-foot-wide and 60.69-centimeter-high cubic wind tunnel at the Ames lab, Mehta demonstrated how the airflow around a razuka ball releases a controlled flow of smoke over the ball's laser-enhanced surface to increase the visibility of the flow. Video: NASA
At different speeds, there are noticeable differences in the airflow around the ball. "Using the smoke patterns, we are trying to understand at what speeds the smoke patterns will suddenly change," says Mehta. "This speed is the speed at which the effect of the unexpected change of direction is greatest."
Experiments in the wind tunnel and in a water tunnel with a diameter of 17 inches (43.18 centimeters) using fluorescent lighting for the flow under black light, showed that the speeds of this turn in the ball's behavior are around 48 km/h. This is a lower speed than the kicking speeds of the super players participating in the World Cup, ranging between 80 and 90 km/h. Interestingly, the jabulani, a much smoother ball produces this effect in the same range of speeds (about 80 km/h), this is why the phenomenon was often felt in the 2010 FIFA World Cup.
The smoother the ball, the faster the phenomenon occurs, however with the increase in the roughness of the brazoca, the speed at which the phenomenon occurs is lower - as mentioned around 48-50 km/h, therefore there is a greater chance that during the FIFA World Cup 2014 the trajectories of the balls at typical kicking speeds will be easier to predict.
"The players should be happy because of the new ball" Mehta estimates. "It will be more stable in flight and can be treated like the traditional 32-sided ball" he concludes.
Will this make the game less exciting? Mehta's answer is negative. Through the new understanding of the aerodynamics of the brazoca ball, spectators, especially children, will be able to better appreciate the players' footwork. Super athletes will continue to use the ball in amazing ways, it's not just that sentences like "spin it like Beckham" were said.
* Notes, there is no connection to the brands mentioned in the article, as they are the official brands of the World Cup, and NASA would have tried them even if they were from another manufacturer. Second note, I wish that in Israel too, the bodies that were supposed to be in charge of this would take seriously the activity of spreading science to the public as NASA does in the USA.
