The World Cup ball has the aerodynamics of a champion

The players will use a new ball at the World Cup. A lot of work goes into making sure that every new World Cup ball feels familiar to players, because the last thing competitors want is for the most important piece of equipment to behave in unexpected ways.

I teach physics at the University of Lynchburg. There is still beauty in soccer despite the controversy surrounding the World Cup. Every four years I do an analysis of the World Cup ball to see what went into creating the most beautiful game in the world.

The physics of drag

There are a lot of important moments in a soccer game when the ball is in the air. One of the most important characteristics of a soccer ball is how it moves.

As a ball moves through air, a thin layer of mostly still air called the boundary layer surrounds some part of the ball. At low speeds this boundary layer will only cover the front half of the ball before the flowing air peels away from the surface. In this case, the wake of air behind the ball is somewhat regular and is called laminar flow.

The boundary layer surrounds the ball when it's moving fast. In a series of chaotic swirls, the flow of air separates from the ball. The process is called turbulence.

The drag coefficient is a term used by physicists to calculate how much force air exerts on an object. The more drag an object feels, the faster it is.

The drag coefficients of soccer balls are 2.5 times larger than for turbulent flow. Roughening a ball's surface delays the separation of the boundary layer and keeps a ball in turbulent flow. The reason golf balls fly so far is because they feel less drag.

When it comes to making a good soccer ball, the speed at which the airflow transitions is important. The ball slows down dramatically when that transition occurs. The ball slows down more quickly if the flow is too fast.

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Evolution of the World Cup ball

Adidas has supplied balls for the World Cup since 1970. Through 2002, each ball was made with the iconic 32-panel construction. The 20 hexagonal and 12 pentagonal panels were traditionally made of leather and stitched together.

The World Cup was the beginning of a new era. The Teamgesit ball was made of synthetic panels that were thermally bonded together instead of stitching. Water was kept out of the interior of the ball when it was wet.

The way the ball flies through the air can be changed by making a ball out of new materials and using fewer panels. Over the past three World Cups, Adidas tried to balance the panel number, seam properties, and surface texture to create balls with just the right aerodynamic characteristics.

The textured panels on the Jabulani ball were used in the 2010 South Africa World Cup. Many players complained that the Jabulani decelerated abruptly, despite Adidas efforts. The 2006 Teamgesit ball had a higher drag coefficients than the Jabulani ball, which was too smooth overall.

There were six oddly shaped panels on the World Cup balls for Brazil and Russia in the past. They had the same aerodynamic properties even though they had slightly different surfacetextures. Some players complained about the Telstar 18's tendency to pop easily.