Best free kick ever by Roberto Carlos was no fluke, claim scientists
Published 02/09/2010 | 11:47
One of the most incredible goals in international football was no fluke, physicists claim after working out the science of the seemingly impossible free kick.
Brazil's Roberto Carlos kicked a shot from 115ft against France in 1997 which was seemingly heading for the corner flag but it curved like a banana to land in the net.
The bend was so pronounced that the French goalkeeper Fabien Barthez made no move for the ball thinking it would go safely clear.
A ball boy 30ft away from the goal also ducked thinking it was going for him until astonishingly the ball made a last moment sweep left and landed in the back of the net.
His free kick in the Tournai de France has been written off by many as an incredible lucky chance that held France to a frustrating draw. One theory is that it must have been helped by a gust of wind.
But now scientists have applied the laws of physics to settle the matter.
They computed the trajectory and showed that Carlos' goal was no fluke.
Using tiny plastic balls and a slingshot, the French research team from the École Polytechnique in Palaiseau near Paris varied the velocity and spin of balls travelling through water to trace different trajectories.
While their research quickly confirmed the long known Magnus effect, which gives a spinning ball a curved trajectory, their research revealed fresh insight for spinning balls that are shot over a distance equivalent to Carlos' free kick.
The friction exerted on a ball by its surrounding atmosphere slows it down enough for the spin to take on a greater role in directing the ball's trajectory, thereby allowing the last moment change in direction, which in the case of Carlos' kick left Barthez defenceless.
The researchers refer to their discovery as the 'spinning ball spiral', comparing the spiralling effects of Carlos's kick with the shorter distance (80ft) "circular" free kicks shot by the likes of David Beckham and Michel Platini.
As Christophe Clanet and David Quéré, researchers from École Polytechnique, said: "When shot from a large enough distance, and with enough power to keep an appreciable velocity as approaching the goal, the ball can have an unexpected trajectory.
"Carlos' kick started with a classical circular trajectory but suddenly bent in a spectacular way and came back to the goal, although it looked out of the target a small moment earlier.
"People often noticed that Carlos' free kick had been shot from a remarkably long distance, we show in our paper that this is not a coincidence, but a necessary condition for generating a spiral trajectory," he said.
The research is published today in the New Journal of Physics,