So that Ronaldo and Co. can «conjure»

Empa researchers investigate tournament footballs - also for the 2018 Football W
Empa researchers investigate tournament footballs - also for the 2018 Football World Cup in Russia.

The official ball for the 2018 FIFA World Cup in Russia has received Empa’s «OK» after numerous tests. Some goalkeepers may be critical of its flight characteristics, but the reason for their criticism may lie somewhere else - the rather unconventional appearance of the new ball.

Football lives on emotions. When it comes to this year’s World Cup ball, however, Empa’s experts are completely unemotional. When asked about their impression of the flight characteristics of the Adidas model «Telstar 18», which have already been criticized many times: «Impressions are something subjective,» says Martin Camenzind of the «Laboratory for Biomimetic Membranes and Textiles». «We rely on objective parameters that characterize the Telstar 18.» That critics such as Spain goalkeepers David De Gea and Pepe Reina or the German goalie Mark-Andre ter Stegen accuse the ball of «fluttering» is therefore hardly impressive for Camenzind. In any case, the Telstar 18 has successfully passed the test series specially developed at the Empa in St. Gallen for official tournament soccer balls, and that’s what counts for the Empa researcher.

On behalf of FIFA, Empa has been conducting the incorruptible series of tests on footballs striving for the FIFA quality programme’s seal of approval for 22 years. Not every ball passes the test. It is not only the circumference and weight of the ball that are measured here. In addition, despite being crushed 250 times in a water tank, it may only absorb a minimal amount of liquid, must be able to hold its air and always jump off at the same height when it impacts from a height of two metres. To prove that it is a perfect ball, the ball is also measured at no less than 4000 points. And finally, this bullet must retain its shape even if it was shot against a steel wall 2000 times at 50 kilometers per hour.

Such standards also determine the quality and consistency of the sport. When the test series were introduced, not all manufacturers succeeded in achieving the required properties: «Time and again, specimens failed,» recalls Camenzind. Some leather balls would have increased in size considerably after the procedure or absorbed too much water. Today’s balls are glued or welded, because seams could give way over time. Likewise, most of the traditional leather has given way to plastics, the surface of which is specifically textured, which should enable the ball to be guided more easily, especially when wet in the field.

And it is precisely this surface that is responsible for the unpredictable flight of the ball, critics report. Telstar 18 is a strange, fluttering copy, claim goalkeepers of various World Cup teams who have already been allowed to test the ball. But Camenzind countered: «Optics also comes into play here,» explains the engineer. Telstar 18 is not made up of the traditional hexagons and pentagons, but of irregular elements with asymmetrical prints. Thus, the flying ball can be quite an unusual sight under appropriate lighting conditions. «In a study with a computer-controlled foot, we were able to show that balls with flapping flight behavior were by no means so in the experiment under defined conditions.

The fact that the trajectory of a football is a complex and sometimes chaotic matter anyway, according to the theory of aerodynamics, is taken advantage of by real experts. Unlike a streamlined projectile that describes a perfect parabola, the ball deforms, for example when the player kicks it. «The deformation caused by the impacting foot initially gives the ball a somewhat wobbly movement,» explains Camenzind. Good players took advantage of this effect, according to the motto «bend it like Beckham». However, this is not actually a matter of magic, but of accurately applied physics. And this must be well rehearsed, because as soon as the foot is on the ball for a few milliseconds, the player can no longer deliberately influence his movement. There is simply not enough time to direct nerve impulses from the foot to the brain and to send tactically sophisticated feedback to the muscles of the player. And so, in the brevity of the shot, the physics of foot and ball must fit perfectly. Balls of consistent quality contribute to this success.