Published on 15 May 2017
Match Irlande contre Roumanie 2005 @Joe Wicklow

The French tournament of the rugby sevens world series took place on May 13 and 14 - an opportunity to show just how much this sport can gain from a physicist's perspective.

We all know rugby is a very physical sport, but have you ever thought about the physics of rugby? Just understanding how the ball moves is much more complex than you might expect, as ENSTA ParisTech researcher Jérôme Perez has shown. This astrophysicist decided to look into the physics of rugby and discovered some exciting phenomena.

“Together with Christophe Clanet, a researcher at the LadyX laboratory at École Polytechnique, we showed that the speed of a ball when kicked equals twice the speed of the foot at the moment of impact,” said the physicist. “Now, this speed is related to leg length, because of leverage. So the taller you are, the harder you are likely to kick.” Provided you're also well enough muscled to prevent your foot losing speed on impact".

Theory and practice

Dr. Perez has also worked with the Massy rugby team (Essonne) on line-outs. Each thrower has his or her own technique. By analyzing their throws, strategies can be defined to maximize a team's chances of recovering the ball. The French national team is currently taking an interest in this research.

The scrum is another part of the game to fascinate physicists. With a robot made by Thalès, the French team can simulate a scrum against another team. The way the players push and the stresses they are subjected to can then be analyzed. “What we see is that these forces are close to those capable of breaking bones”, warned Dr. Perez, who has reported this to the French rugby authorities.

Players generally know how to make the right moves, but they don't understand why. “Rugby has enormous potential for scientific analysis; this is only the beginning”, said the researcher enthusiastically. He now plans to study specific plays in more detail, such as the fastest try in history, scored six seconds after kick-off.