Its all about the curl

Fluke or skilful – just how much did Roberto Carlos know about the science of ‘that’ goal in the 1997 Tournoi de France?

Some people consider the goal – a free kick with a powerful curling trajectory from 35m – to be just a fluke, a lucky strike that curved at the last minute. Others think the Brazilian winger was able to shoot – and score – from such a distance because he knew exactly how to.

Well now French physicists – perhaps looking back to a time when the national team was held in high regard (1997 was the year before they won the World Cup) – think they’ve figured out why Carlos’ goal went in. It’s all in the curl.

Using tiny plastic balls and a slingshot, the research team – based at the École Polytechnique in Palaiseau – studied the velocity and spin of balls travelling through water to trace different trajectories.

Their research quickly confirmed the Magnus effect – which gives a spinning ball a curved trajectory – but revealed that the friction exerted on a ball by its surrounding atmosphere slows it down enough for the spin to take on a greater role in directing the ball’s path. This allowed the last minute swing to the left to bring Carlos’s kick inside the post – leaving French goalkeeper Fabien Barthez rooted to the goal-line thinking the ball was going wide, and the ball boy to the right of the goal ducking for cover. The team called this effect the ‘spinning ball spiral’ – very original.

“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,” researchers Christophe Clanet and David Quéré wrote, “Carlos’ kick started with a classical circular trajectory but suddenly bent in spectacular way and came back to the goal, although it looked out of target a small moment earlier.” So the science is there – the goal was no fluke they claim, but how much did Carlos know about the science behind his free kick?

Probably not much. As any footballer is bound to do – Carlos probably practiced taking free kicks from various distances over and over again. He’d know precisely how hard to strike the ball – and with legs the size of tree trunks it can’t have been too difficult – and in what direction with which part of his boot.

The goal can’t have been a fluke, but I doubt Carlos much considered the science of his amazing goal. He’s scored several others of similar quality from similar region – practice makes perfect after all!

And we can’t forget the English National Treasure – the talismanic saviour of our football (who was so cruelly told his England days were over by manager Fabio Capello) – David Beckham. His right foot – and probably his left foot too – must be ensured for millions and we all know the quality of his free kicks.

Although his strikes are typically from closer range – usually around 20 to 25m – and take on a circular motion, you can’t deny some of those have been amazing. But I’m almost positive that Beckham has not considered the science behind his free kick taking – I imagine it’s a similar scenario to Carlos, hours and hours of practice to perfect the perfect strike.

Whether the likes of Carlos and Beckham understand or even care about the science behind their masterpieces I can’t be sure, but what I do know is that they make some brilliant – and jaw dropping – moments in football.

To see a video of Carlos’ goal, check out Roberto Carlos free kick vs France under Lab News Recommends at www.youtube.com/labnews