Scientists explain ‘the kick’

PARIS – Thirteen years after Roberto Carlos stunned onlookers with his amazing “banana” free kick that seemed to defy the law of physics, scientists finally have figured out just how he did it.

In what many people regard as the best free kick in the history of the game, the Brazil defender struck the ball with the outside of his left foot from 35 yards away, bending it around the outside of France’s three-man wall during an exhibition tournament in Lyon in 1997.

The ball looked way off target to the right – a ball boy standing 10 yards from the goal even ducked his head – 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 told the Associated Press. “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 the speed of more than 60 mph – approximately the speed of 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 40 yards with a soccer ball. As the ball slows, the “Magnus effect” becomes increasingly pronounced, which eventually creates 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.