Greatest free-kick 'was no fluke' say physicists

[Red Mango]

http://www.bbc.co.uk/news/science-environment-11153466

 By Victoria Gill  Science reporter, BBC News
Roberto Carlos (Getty Images)

Physicists have explained one of football's most spectacular goals.

Brazilian Roberto Carlos's 1997 free-kick against France curved so sharply that it left goalkeeper Fabian Barthez standing still and looking puzzled.

Now, a study published in the New Journal of Physics suggests that the long-held assumption that the goal was a fantastic fluke is wrong.

A French team of scientists discovered the trajectory of the goal and developed an equation to describe it.

They say it could be repeated if a ball was kicked hard enough, with the appropriate spin and, crucially, the kick was taken sufficiently far from goal.

Roberto Carlos scored his wonder goal during the inaugural match of the Tournoi de France, a friendly international football tournament that was held in France ahead of the 1998 World Cup.
Follow the curve

Many pundits referred to it as "the goal that defied physics", but the new paper outlines the equation that describes its trajectory exactly.

"We have shown that the path of a sphere when it spins is a spiral," lead researcher Christophe Clanet from the Ecole Polytechnique in Paris told BBC News.
Graphic of Roberto Carlos's free kick

Dr Clanet described this path as a "snail-shell shaped trajectory", with the curvature increasing as the ball travels.

Because Roberto Carlos was 35m (115ft) from the goal when he kicked the ball, more of this spiral trajectory was visible. So the apparently physics-defying sharp turn of the ball was actually following a naturally tightening curve.

Dr Clanet and his colleague David Quere were studying the trajectory of bullets when they made their sporting discovery.

They used water and plastic balls with the same density as water to "simplify the problem".
Long flight

This approach eliminated the effects of air turbulence and of gravity and revealed the pure physical path of a spinning sphere.

"On a real soccer pitch, we will see something close to this ideal spiral, but gravity will modify it," explained Dr Clanet.

"But if you shoot strongly enough, like Carlos did, you can minimise the effect of gravity."

The crucial aspect of the wonder strike, according to the scientists, was the distance the ball had to travel to beat Fabian Barthez.

"If this distance is small," said Dr Clanet, "you only see the first part of the curve.

"But if that distance is large - like with Carlos's kick - you see the curve increase. So you see the whole of the trajectory."

[dinho]

Scientists uncover secret of Roberto Carlos goal

http://msn.foxsports.com/foxsoccer/latinamerica/story/Scientists-uncover-secret-of-Roberto-Carlos-goal

<a href="http://www.youtube.com/v/Pl0LHM-33Io" target="_blank" rel="noopener noreferrer" class="bbc_link bbc_flash_disabled new_win">http://www.youtube.com/v/Pl0LHM-33Io</a>

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 35 yards (meters) out, bending it around the outside of France's three-man wall during a friendly tournament in Lyon in 1997.

The ball looked way off target to the right - a ball boy standing 10 meters (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 100 kph - 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 40 meters (yards) with a football. As the ball slows down, the "Magnus effect" becomes more and more 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.

"When Michel Platini or David Beckham were kicking free kicks from 20 meters, 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.

"Another player could repeat it - on the condition that the ball is kicked hard enough, that the kick is taken from about 40 meters and that the player gives some effect to the ball."

Roberto Carlos claimed at the time he had done it all before, against Roma when he was playing for Inter Milan, although he never quite managed to repeat his 1997 trick.

"It's difficult to say whether it was a lucky goal," Quere said. "There is something close to perfection in this trajectory that let me think that Roberto Carlos has probably always taken these kinds of free kicks from long range, and he should have realized that he could take advantage of it."

Barthez said after conceding the goal that he didn't set his wall correctly, but Quere said the goalkeeper probably just thought Roberto Carlos had fluffed his shot.

"Barthez was a very good keeper, at the peak of his art," Quere said. "But the trajectory was eccentric and he didn't move."

[weary1969]

U C Y DEY HAD 2 OBEAH DEM IN D 98 FINAL. Could neva get tired watching that