Tuesday 4 September 2018

The Science Behind Football: Roberto Carlos’ Immortal Kick

Hi Internet pals, today we are going to cover the world’s most popular sport – football (or soccer). Physics can explain some of the aw-inspiring plays performed by top players - bicycle kicks, diving headers and fingertip saves all exemplify the conservation Newton’s laws. Perhaps, one of the most interesting physics phenomena in football, explains the curve behind a long distance free kicks.

On June 3, 1997, 21 years ago, in a game between France and Brazil, a young Brazilian player named Roberto Carlos set up for a 35 meter free kick. With no direct line to the goal, Carlos decided to attempt the seemingly impossible. His kick sent the ball flying wide of the players, but just before going out of bounds, it hooked to the left and soared into the net. This is Roberto Carlos’ most famous goal of his career and arguably in the history of football.

According to Newton’s 1st law of motion, an object will move in the same direction and velocity until a force is applied to it, regardless of the strength of the force. When Carlos kicked the ball, he gave it direction and velocity, but what force made the ball swerve and score one of the most magnificent goals in the history of the sport?

The trick was in the spin…

Carlos placed his kick at the lower right corner of the ball, sending the ball high and to the right, but also rotating around its axis. The ball started its flight in a direct route, with air flowing on both sides and slowing it down.

On one side, the air moved in the opposite direction to the ball’s spin – causing increased pressure, while on the other side, the air moved in the same direction as the spin, creating an area of lower pressure. The difference between the pressures made the ball curve towards the lower pressure zone.

This phenomenon is called the Magnus effect. This type of kick, also commonly known as a banana kick. The Magnus effect was first documented by Sir Isaac Newton after he noticed it while playing a game of Tennis back in 1970.

The sweeter you hit it, the more swerve you get, and Roberto Carlos caught it just right. The way it worked out, it was perfection. The free kick left Fabien Barthezc – France goalkeeper in hopeless despair and befuddlement as the ball fizzes back from yards outside of his left-hand post. It is the free kick that makes the beautiful game, beautiful.

“There are lots of good kickers nowadays, it might take some time but someday someone will score a similar goal. But I was the first.” – Roberto Carlos

Check out more fun and interactive story of science and technology at Petrosains the Discovery Centre!

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