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Blog

Brazilian wondergoal was no fluke, say physicists

By James Dacey

By many fans it is considered to be one of the most brilliant (soccer) goals ever scored, but by others it is dismissed as a bizarre fluke probably caused by rare atmospheric conditions.

The free kick scored by Brazilian fullback Roberto Carlos against France in 1997 is said to have “defied physics” on account of its wicked late swerve that stunned both the French goalkeeper and thousands of fans.

Now, 13 years on, physicists in France say that they can finally explain what happened and they believe that the wonder strike was no fluke.

On that early summer night in Lyon, Carlos struck the ball at around 35 m from the French goal. It was heading so far to the right that it initially cleared the wall of defenders by at least a metre and made a ballboy, who stood metres from the goal, duck his head. Then, almost magically, the ball curved to the left and entered the top right-hand corner of the goal.

In all the talk over the years, pundits and the occasional scientist have suggested a number of possible causes. They range from a gust of wind, to a materials effect in the ball, to unusually dry localized conditions as explained in this Physics World feature article from 1998. But the case has never been closed.

Guillaume Dupeux and his colleagues at the Ecole Polytechnique in Palaiseau have taken a more practical approach by modelling the flight of the football in a more controlled environment, firing tiny polymer spheres through water using a slingshot.

The lightness of the balls and the density of water enabled them to track the tiny spheres as they moved through a spiral which rotates in progressively smaller orbits. The researchers dub this the “spinning ball spiral effect” and explain that we only see this when friction allows the spin effects to become comparable with the forwards trajectory.

planeterellasmall.jpg
Tracking the trajectory of plastic spheres in water

Dupeux’s group argues that, before it smashed into the back of the net, Carlos’ free kick had also begun to follow a spinning ball spiral, which accounts for the fact that it seemed to bend significantly more at the end of its flight. The Brazilian skill came in because Carlos had kicked the ball with enough power and spin, from far enough out, for the spiral to take effect.

It’s a shame Carlos never quite managed to repeat the trick, but at least now we know it was worth him trying!

The research is published today in New Journal of Physics.

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2 comments

  1. Graham Rounce

    I’m sure it’s repeatable. I suppose a research project with a mechanical foot and a football would be just what wouldn’t get funded now.

  2. Anton Szautner

    You must be kidding…and Doupeux’s group must be plumb out of their minds.
    Sure the ball deflected in a curve departing from gravitational influence alone while in flight due to spin, according to the orientation of its applied spin axis through the air. That’s what spinning objects do when moving in an airstream, a well-known elementary aerodynamic effect.
    One cringes at the over-dramatic descriptions of a trivial sporting event so easily corrected by watching the (literally lousy) video: we read, for example, “…before it smashed into the back of the net” (when it CLEARLY bounced off the inner edge of the goal post, how “smashing” can that have possibly been?) and “…Carlos’ free kick had also begun to follow a spinning ball spiral, accounts for the fact that it seemed to bend significantly more at the end of its flight” (duh, which is laughable since “seemed” is hardly diagnostic of what actually happens) and, “Then, almost magically, the ball curved to the left and entered the top right-hand corner of the goal” which patently, observably, is pure nonsense, since it is quite clear in the video that the ball struck the inner edge of the post at the height of a man, NOWHERE NEAR a “corner” of the goal as the conventional definition of corner has it, and EASILY WITHIN THE ABILITY OF A GOAL TENDER TO DEAL WITH IT WITHOUT EVER LEAVING THE GROUND. Furthermore, that ball was clearly kicked far OVERHEAD – NOT just too far laterally to their side – of any of the “wall of defenders”, for them to ever have been able to reach let alone block that ball. They were NOMINALLY “out of place”, and Carlos kicked a ball that overshot them AND curved around enough to enter the goal.
    Leave the tawdry hyperbole to sportcasters. Somehow, they don’t sound nearly as silly while broadcasting live as a physicist does preserving a legendary event 13 years after the fact, especially with lots of video footage that so embarrassingly contradicts the tiresomely inaccurate account of Something Special having transpired.
    There’s nothing mysterious in it, it isn’t a “bizarre fluke”, and there is nothing whatsoever at all about it to be “stunned” over. Not even after all of these 13 years, after the artifice of ‘legend’ has had time to incubate and insinuate its way toward transforming the tawdry and trivial into miracle.
    The effect has been appreciated for a a very long time, from pitched American baseballs to toys that employ back-spin for lift. But it is especially embarrassing to see it having moved some French physicists so stunned by their national loss that they would bother to contrapt an ‘experimental apparatus’ involving “firing tiny polymer spheres through water using a slingshot”…into a STRONG DENSITY gradient of LIQUID water (not to mention the complexities involved in entry into the surface for finite-sized spheres, however their surfaces may or may not be textured like a football), and then dutifully reported here as “a more controlled environment” purporting to to inform us of a solution to the great mystery of how spinning footballs behave while moving through air of constant pressure, if not quite so constant wind conditions.
    Unfortunately, the experiment does not much enlighten on how a goal tender can be so thoroughly eluded, or how so many can be deluded into imagining that a ball with considerable spin can’t possibly get by one unless it defied physics or was, at least as such freakish events go, in a class all by itself.
    LAUGHABLE I say. Worse. As preposterous as a vivuzela is obnoxious. Patently IDIOTIC I say.
    This idiocy should have died with Physics World’s FIRST article on the matter, back in 1998. A dozen years later it regurgitates upward to haunt us once more, like a dormant disease which periodically triggers the symptoms of uncontrollable eye-rolling and frothing at the mouth.
    There was no “bizarre fluke probably caused by rare atmospheric conditions”, it did not “defy physics” and there was no unusually “wicked late swerve”. Anybody who thinks so is a lousy observer who is evidently incapable of segregating a zeal for a game or allegiance to a team from the ordinary responsibilty of ordinary observation.
    There is in my humble opinion one and one reason only why that goal was scored: the goal tender is respoinsible for keeping the ball out of his domain. He utterly failed to move in the required direction: he saw that ball embark upon an unusual angle which he THOUGHT UNLIKELY TO ENTER THE GOAL, and reacted by not bothering to react. Period. He failed as a goal tender.
    Sob, sniff. Oh the agony of defeat.

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