Soccer Players or Turbulent Particles? Physics Say They Act Alike

Physicists have studied many phenomena, such as soccer players' movements, to better understand turbulence. This photo was taken during an Australia-Germany match on June 19 2017. Carl Recine / REUTERS

New research shows the way soccer players move about the field bears similarities to the manner in which particles behave under the chaotic conditions of turbulence.

This discovery is one of the many made in an effort to better understand turbulence, which is a surprisingly active and pressing field. More than half a millennium after Leonardo Da Vinci first coined the term, in 1507, physicists still don't have a complete understanding of what goes on under conditions of turbulence, and no equation exists to accurately describe the phenomenon. That matters greatly, because turbulence is one of the primary enemies of efficiency. If the behavior of particles in turbulent conditions was better understood, it could probably save billions of dollars by allowing for more efficient vehicles, aircraft and ships, and even spare lives. Indeed, turbulence routinely causes injuries and deaths. Just this week, on June 20, a United Airlines flight encountered turbulent conditions between Panama City and Houston, which led to the injuries of at least nine passengers and one crew member.

For a study published in the journal Physical Review Fluids, Wouter Bos, a Dutch researcher at the French National Center for Scientific Research, and colleagues searched for real-life examples of phenomena that could help them model turbulence and happened upon soccer — or, as most of the world calls it, football. These athletes zip about the pitch somewhat like particles churned up by turbulent flow constrained within a rectangle.

The way soccer players shift directions somewhat resembles particles within a turbulent flow. Benjamin Kadoch et al / Physical Review Fluids

In the paper, co-authored by researchers Kai Schneider and Benjamin Kadoch, the scientists "demonstrate that football players change direction, on average, like fluid particles. From this point of view, confinement by the sidelines of the football-field reproduces the same effects as solid boundaries on fluid particles," Bos says.

Michael Wilczek, a researcher at the Max Planck Institute for Dynamics and Self-Organization, who wasn't involved in the paper, says he doesn't think that soccer players move terribly similarly to turbulent particles. However, he says that "the comparison of trajectories from various 2D flows with the ones of soccer players helps to disentangle effects that are system-specific from ones that are more universal and imposed by confinement," and is a valuable contribution to the field.

Over the last few years, analytical techniques, deriving from complex math and physics, are increasingly being adopted by sports teams to give them an advantage. Although Bos doesn't think that this specific study would help a soccer club get ahead just yet, "it does illustrate how the tools from physics and more precisely fluid mechanics can be used in the field of sports analysis. Indeed, the last two decades have seen a wealth of [new] tools to characterize the movement of fluid particles in turbulent flows, and to better understand the intriguing complexity of turbulence." Eventually these methods and insights "might also help to better understand how a football or soccer player could use [his or her] force and energy in the most rewarding way," Bos says.