Thirteen years after Roberto Carlos stunned onlookers with his amazing “banana” free kick that seemed to defy the law of physics, scientists have finally worked out just how he did it.
In what many people regard as the best free kick ever, the Brazil defender struck the ball with the outside of his left foot 35m out, bending it around the outside of France’s three-man wall during a match in Lyon in 1997.
The ball looked way off target to the right — a ball boy standing 10m from the goal even ducked — but at the last moment, it swerved dramatically inside the post and into the net. The bewildered France goalkeeper, Fabien Barthez, had not even moved.
Many people thought the shot was a fluke, but researchers say it can all be explained by science.
“What happened that day was so special,” researcher David Quere said. “We are confronted with an unexpected law of physics, but it’s possible to see this again.”
Quere, a physicist at the ESPCI and Ecole Polytechnique in Paris, and his colleagues have developed an equation to explain the bizarre trajectory of the shot. Using a small pistol to fire bullets into water at 100kph — approximately the speed of Roberto Carlos’ shot — they discovered that the path of a sphere when it spins is actually a spiral.
Quere said the study, which has been published in the New Journal of Physics, confirmed the “Magnus effect” — which is responsible for the curved motion of a spinning ball — but it also revealed what the scientists call the “spinning ball spiral.”
The spiral effect appears after about 40m with a soccer ball. As the ball slows, the “Magnus effect” becomes more pronounced, eventually creating a spiral.
“The crucial thing is that while the ball is slowing down, the rotation is the same,” Quere said. “Hence the trajectory of the ball is going to be more and more bent, that is what creates the spiral.”
“When Michel Platini or David Beckham were kicking free kicks from 20m, they were bending the ball in an arc. It’s not the same thing with Roberto Carlos’ goal. He can have this kind of effect because he kicks from long range,” he said.
“Another player could repeat it — on the condition that the ball is kicked hard enough, that the kick is taken from about 40m and that the player gives some effect to the ball,” Quere said.