Scientists solve mystery behind Roberto Carlos magical free-kick

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Thirteen years after Roberto Carlos stunned onlookers with his famous 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 Brazilian fired home a long-distance free-kick against France in 1997 which forced a ball-boy to duck, thinking it was going to hit him before it curled back in past a motionless Fabian Barthez.

Some had attributed it to accuracy, others called it a fluke, but researchers say it can all be explained by science.

Dr Cristophe Clanet and his colleague David Quere, researchers from École Polytechnique in Paris, were looking at the trajectory of bullets when they made their sporting discovery.

Using a small pistol to fire bullets into water at the speed of 100 km/h - approximately the speed of Carlos' shot - they discovered that the path of a sphere when it spins is actually a spiral.

Carlos is known to kick hard and the ball's speed practically canceled out gravity, allowing the spiral to come into play.

The scientists proved that the crucial aspect of the wonder strike was the distance the ball had to travel before reaching the goal as this directly related to how much of the spiral could be seen.

Because Carlos was 35m (115ft) from the goal when he kicked the ball, more of this spiral trajectory was visible.

If Carlos had been any closer, the ball would have missed the goal before it had a chance to curve around.

And if he had kicked the ball from any farther back, the ball might have curved too much and shot past the goalposts, or hit the ground and lost the spiral.

"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," the researchers wrote in the New Journal of Physics.

"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."

So did Carlos know what he was doing when he made that kick, or was it purely accidental?

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