Physical forces describe how objects interact with their environment. For example, you can use physical forces to predict the trajectory of a kicked soccer ball.

Social forces describe how people react to social information they perceive from their environment. For example, you can use social forces to predict how a soccer player will move in response to the other players on the field.

A snapshot of four players during the ball possession game, with an overlay of the triangle used to describe the location of the offensive players.

Image Credit: Keiko Yokoyama, Hiroyuki Shima, Keisuke Fujii, Noriyuki Tabuchi, and Yuji Yamamoto, Physical Review E.

A diagram of the physical guidance tool developed by the researchers.

Image Credit: Keiko Yokoyama, Hiroyuki Shima, Keisuke Fujii, Noriyuki Tabuchi, and Yuji Yamamoto, Physical Review E.

Even Michael Jordan needed teammates. Makeshift stands selling Bulls merchandise inhabited every corner of Chicagoland after “Air Jordan” led his team to their third straight championship in 1993—and all the stands were busy. People were caught up in the excitement and inspiration of watching Jordan, Pippen, Armstrong, Grant, and their teammates take on the world.Not only are great teams inspiring, they can also accomplish huge feats and solve important problems. Teams like the staff of the Manhattan Project and members of the “ PayPal Mafia ” wrote critical chapters of US history and set the course for its future.But what makes a team successful? The skills of the individuals matter, of course, but a team of experts doesn’t always make an expert team. Having the best player—even the best player of all time—doesn’t necessarily make the best team either.Scientists regularly turn to psychology and neuroscience to study teamwork and cooperation, but it turns out that physics has something to say about the matter too. In new research published in the American Physical Society’s journal, a team of Japanese scientists lays out a simple model based on “social forces” that provides insight into the social skills necessary for excellent team coordination.Led by Keiko Yokoyama and Yuji Yamamoto at Nagoya University, the team focused their attention on this question: Which social skills are indispensable for players in a ball possession game? The game, an exercise that promotes team coordination, involves four players. Three players are on the offensive, aiming to pass a soccer ball as many times as possible in 90 seconds. The fourth player intercepts the ball as often as possible.The researchers recorded groups of rookie and experienced players playing the game. There were eight groups and each played four rounds, with players rotating among the positions. From the videos, the researchers extracted the positions of the players at different times.Analyzing this data, a pattern emerged—when on the offensive, teams of experienced players maintained the formation of an equilateral triangle—a triangle with equal sides and equal angles. Rookie players, on the other hand, were all over the place and their positions usually formed a triangle that was far from equilateral.Put another way, the experienced players demonstrated more coordinated movements, physically reacting to one another in a way that increased the success of their team. It was as if some invisible force was keeping them in alignment. The researchers hypothesized that this was the result of a combination ofAt any given time, the offensive team includes aand a(who isn’t involved in the current pass, but moves in preparation to be the next receiver). The researchers hypothesized that an experienced receiver is solely focused on chasing the ball and isn’t influenced by social forces. However, they theorized, the passer and mover are influenced by the following three social forces:• Spatial force—the psychological motivation to stay within the boundaries, similar to the "boundary conditions" that keep a particle contained in a certain region of space• Avoidance force—the psychological motivation to stay away from the defender, which can be modeled as a repulsive force• Cooperative force—the psychological motivation to pay attention to the location of your teammates and stay close to one another, which ends up acting like an attraction to both teammates.Next, the researchers set up a mathematical model of these forces based on an approach commonly used in physics. Using this model, they ran simulations to see how offensive players would move relative to one another for various strengths of the three social forces.The results of the simulations show that a high cooperative social force leads to the same type of coordinated movement the researchers saw among experienced players. Similarly, a low cooperative force leads to the same uncoordinated movement they saw among rookies.Taking this one step further, the researchers developed a physical tool for turning the invisible cooperative force into a physical force. The tool consists of three equally long elastic bands forming the sides of a triangle, with a waist belt connecting them at each point. When people play the ball possession game wearing the waist belts, the bands stretch or slack according to the distance between the players. This feedback helps players move in a coordinated way. The tool drastically improved the coordinated motion of rookie players, say the researchers, although it did nothing to improve their ball handling skills!All in all, this research suggests that the social force model is a valid way to study how invisible forces, like interpersonal skills, influence the success of teams. The researchers point out that using this model, we can now explore the social forces behind other collective activities, identify the social forces that matter most to the success of these activities, and develop tools to promote these skills. That’s pretty good work for a team of academics!