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(Inside Science) – Cristiane Rozeira’s left foot hit the ball from the whistle. The ball soared over the barrier, curved gracefully to the right, struck the post and crossed the goal line. It was Rozeira’s third consecutive score in the match, and with it, she secured Brazil’s victory over Jamaica in the 2019 FIFA Women’s World Cup, which is held in France.
Scoring this goal was no small feat. It took expertise, but also a well-designed ball.
This year’s official ball, the Conext 19, has virtually the same panel design as the Telstar 18, which was the official ball for last year’s Men’s World Cup in Russia. The graphics are different, however, as they are inspired by the 1998 tricolor ball.
The ball used in official matches is designed every four years by Adidas for the Men’s World Cup and normally attracts some criticism. For example, Italy striker Giampaolo Pazzini complained that the 2010 Jabulani weighed less than usual, and German goalkeeper Marc-André ter Stegen said last year’s Telstar 18 “could be better. “.
“The footballers who play are at the absolute elite level,” said John Eric Goff, a physicist at Lynchburg University in Virginia. Even though Adidas makes the technical design of the ball similar to what players have come to expect, he said: “There are going to be small changes, not only in the aerodynamics, but [also in] the way the ball feels when the texture changes slightly, or the panel design changes – they’re going to notice it on their boot. “
Players want to be able to predict the behavior of the ball in rebound, roll, flight, foot speed and grip, wrote sports designer Andy Harland, director of the Sports Technology Institute at Loughborough University in the UK, in an e- mail to Inside Science. “The players are incredibly skilled and when they hit the ball differently they expect it to behave accordingly.”
Goff has been testing soccer balls since 2006. Last year, he and his colleagues Takeshi Asai and Sungchan Hong from the University of Tsukuba, Japan, tested the Telstar 18 and found that the ball’s aerodynamic properties were perfect for a football match.
The aerodynamics of a soccer ball are simple, but the combination of forces and variables must be just right for the ball’s trajectory to bend and deceive a goalkeeper.
“Once the ball has been kicked and is moving through the air, there is really very little force acting on the ball,” said mechanical engineer Anette (Peko) Hosoi of the Massachusetts Institute of Technology. . “There is gravity, there is drag and there is lift.”
In fluid dynamics, drag – or air resistance – is a force opposed to the direction of the ball. It can be influenced by the roughness and seams of the ball. In fact, these seams are essential in making the trajectory of a ball predictable. A smooth ball would be “terrible,” said Hosoi, who founded the MIT Sports Lab.
Imagine the air surrounding a soccer ball in flight. A layer of air circulates around the front and creates a “turbulent and messy” region of high pressure behind the ball, which pushes it forward, Hosoi said. In a straight trajectory, this region would be directly behind the ball, but players like Cristiane like to spin the ball to curve its trajectory. This rotation creates a lateral force, called the Magnus force, which shifts the “disorderly turbulent” region to the side and deflects the ball from its forward path, Harland said.
All of these forces are also impacted by temperature, air pressure and the aerodynamic properties of the ball. “The degree of Magnus strength can be affected by the design and the number of seams,” said Harland. The weather, the player’s shoes and the outer surface of the ball also play a big role in the amount of spin, which ultimately determines the strength of the Magnus force.
Although this year’s Conext 19 only has six panels, the overall ball seam length is 30% longer than the last significantly different design, which was the 2014 Brazuca. This year Asai and Hong have tested the Conext 19 in a wind tunnel and found the aerodynamic properties to be very similar to the Telstar 18, which was expected since the design is the same.
“I imagine there was no technical need to change anything,” Harland said.
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