For fans of world football - still "soccer" to most Americans - it ranks as one of the most amazing goals ever. In a 1997 match against France during the Tournoi de France, Brazil's Roberto Carlos lined up for a free kick. But his shot veered so far to the right of the net that France's goalkeeper hardly moved a muscle trying to block it. That's when the ball took a bizarre turn back to the left, winding up inside the goal.
Where to place Carlos' goal on the all-time list is fodder for countless bar arguments. In fact, the game's aftermath spawned disbelief among supports both of Brazil and France, leading some to wonder whether the shot may even have defied the laws of physics. Hyperbole and sports arguments go hand-in-hand, but after finishing a study of spiral trajectories, researchers say there was nothing unworldly about Carlos' goal. What they found was that in certain sports like soccer, where both gravity and aerodynamics play a comparable role, ball velocity and spin sometimes can produce surprising trajectories.
Writing in the New Journal of Physics Christophe Clanet and David Quere from the Ecole Polytechnique in Palaiseau describe how they tested different trajectories taken by plastic balls as they traveled through water. While the findings confirmed previous research about how a spinning ball assumes a curved trajectory, the research also offers tips for would-be footballers who might find themselves in a similar situation as Carlos. (who was about 115 feet away from the goal when he kicked the ball.) While gravity will affect the ideal spiral, they found that force and distance can help counter its effects.
"The ball trajectory can deviate significantly from a circle, provided that the shot is long enough. Then the trajectory becomes surprising and somehow unpredictable for a goalkeeper. This is the way we interpret a famous goal by the Brazilian player Roberto Carlos against France in 1997. This free kick was shot from a distance of approximately 35 m, that is, comparable to the distance for which we expect this kind of unexpected trajectory. Provided that the shot is powerful enough, another characteristic of Roberto Carlos' abilities, the ball trajectory brutally bends towards the net, at a velocity still large enough to surprise the keeper."