Physicists say 2018's World Cup ball may fly shorter distances than 2014 design
As the world gathers to watch the 2018 FIFA World Cup in Russia, all eyes will be on the ball in more ways than one.
Unlike some of the other prestigious sporting championships around the world, such as the Super Bowl and World Series, the World Cup does something unique: It brings in a never-before-used ball just for this tournament.
Over the years, the ball has been engineered to improve its aerodynamic capabilities. These changes have been a subject of intense scrutiny, particularly with how players are able to manipulate it around the field.
One natural factor that can inhibit or improve ball flight is temperature.
"If you increase the temperature, the mass density off the air goes down, and the drag on the ball is gonna go down, so the ball will travel farther when the temperature increases," said John Eric Goff, professor of physics at the University of Lynchburg in Virginia and author of "Gold Medal Physics: The Science of Sports."
"Humidity does not play nearly as large a role as the temperature change will," he said.
Wind resistance is a major factor in sports and certain sports balls are designed to lower the amount of drag or wind resistance. For example, a golf ball isn't smooth, but rather has hundreds of dimples. A baseball has 108 double stitches that allows a ball to break at certain angles when thrown by a pitcher.
A soccer ball is made of different panels. Up until 2006, soccer balls used in World Cup play consisted of 32 panels, 20 in hexagonal shapes and another 12 in pentagonal shapes.
Controversy ensued at the 2010 World Cup in South Africa when the ball design was reduced to eight panels. The ball, labeled the Jabulani, proved to be a bit unpredictable as it moved through the air, especially on longer free or corner kicks. Some players said its motion resembled a beach ball more than a soccer ball.
"You run the risk of when you reduce the number of panels of the ball getting to be too smooth," Goff said.
The Brazuca, the ball used for the 2014 World Cup in Brazil, had only six panels, but Adidas, the official manufacturer of the ball, made adjustments, such as increasing the seam length and adding texturing to the panels in the form of circular grooves to add a layer of roughness.
The official match ball for the 2018 World Cup is the Telstar 18, a six-paneled thermally bonded ball that weighs less than a pound and has a microchip embedded.
Soccer balls that are thermally bonded, rather than stitched together, eliminate the risk of the ball becoming waterlogged when the game is played on a wet field. A wet soccer ball can be heavier for players to move.
Goff, along with two faculty members from the University of Tsukuba, in Tsukuba, Japan, recently published a paper examining the aerodynamic and surface comparisons between the Telstar 18 and the Brazuca. Their research was published in the "Journal of Sports Engineering and Technology" on May 19.
The group used a combination of experimental methods, including wind tunnel testing and measurement techniques, to determine surface properties of the ball. The results of the wind tunnel tests were used to create model trajectories that illustrate the ball's various flight trajectories.
Temperatures inside the room at the time of testing were between 8 and 16 degrees Celsius while air speeds during testing ranged from 15-80 mph.
"We were able to test essentially the whole range of speeds that you're likely to see in a soccer match," Goff said.
After performing the experiments, the researchers concluded that the Telstar 18's horizontal range for high-speed kicks will be 9-10 percent shorter than corresponding ranges for the Brazuca in 2014. Essentially, the ball is expected to travel shorter differences when kicked at a high speed compared to the Brazuca. They did note that the ball could appear faster for passes over a shorter distance.
A high-speed kick of the ball off the foot of a professional soccer player can be greater than 70 mph, according to Goff, who has been studying the impact of physics and sports since 2002.
The researchers said they are anxious to watch the tournament to see whether their modeling predictions are realized during play.
While the aerodynamic properties of the ball are very similar to the one in 2014, it won't play exactly the same since the panel shapes and textures are different. The elite players, who have an innate feel for the game, can identify even the slightest tweaks to the ball.
Some goalkeepers have already issued complaints about the Telstar 18.
Even with the many quirks of the ball and the need for players to adjust to it, today's technology has improved the ball significantly compared to decades ago.
"These balls right now are far superior to the ones they were using 30 years ago," Goff said.