The secret of the legendary free kick

18 years have passed, but football lovers still remember the seemingly impossible free kick of Roberto Carlos, the Brazilian football player. Now scientists find out the mysteries inside that superb free-kick.

Scientific explanation of Roberto Carlos's thunderbolt shot

Roberto Carlos's penalty kick

The match between France and Brazil took place on June 3, 1997 in the Tu Hung Cup - the tournament prepared for the 1998 World Cup - is an extremely memorable event in football. In the last minute, Brazilian player Roberto Carlos scored an incredible goal from a free kick . At a distance of 35 meters from the goal, Carlos kicked the ball towards the right corner. But when in the air, the ball suddenly changed direction. It turned down and headed to the left, stunned by goalkeeper Fabien Barthez . The ball fits neatly in the net and the score is 1 - 1.

Roberto Carlos made a free-kick that made the orbiting ball unimaginable to the French team in 1997. (Photo: theda.co.uk)

Sciencemag said, to explain this goal, scientists from Polytechnic University in France have expanded their research into the properties of objects that are moving in liquid, including sports balls. . They use a firing device to push the ball in the water. The reason is because of the effect of water on a moving object like the mechanism of air acting on larger balls.

Using computers and high-speed cameras, the team found the characteristics of the balls in the experiment exactly the same as Carlos's incredible shot. Initially when they were fired, they rushed in the water in a straight line. But they immediately changed direction in only 1/1000 second.

Illustration of the ball's orbit after Roberto Carlos's shot.The seamless red line is the trajectory of the ball.It changed direction unexpectedly while flying.The two dashed lines are the trajectories that people think the ball will go through in normal circumstances.(Photo: Wikimedia.)

This phenomenon is partly due to the Magnus effect. The ball rushes forward but also rotates on an axis perpendicular to the direction of the motion. That means that in a water environment, one side of the ball moves faster than the other side creates Magnus force. This force makes the ball's path slightly bent toward faster movement.

However, the resistance of the surrounding environment also reduces the ball speed without much impact on the vortex or Magnus effect. Therefore, the more curved the curve becomes, and finally creates a spiral path , rather than the curve from top to bottom as usual.

With Carlos's shot, research shows that he can only make this perfect shot when standing at an appropriate distance. Both the distance and the strong thrust - about 130 km / h - provide the ball with the speed needed to rush towards the goal before the Magnus effect acts and causes the ball to spin and fly into the net.

Based on experiments in water environments, scientists have developed an equation that accurately describes the movement of plastic balls. By adding data such as initial direction, density, and velocity, they can accurately predict the trajectory of spherical objects that dive in the water.

' The greatest significance of the study is that the vortex phenomenon can be applied to control the trajectory of an object flying in a definite direction ,' said David Quéré, a physicist at Polytechnic University at France commented.

The study is published in the New Journal of Physics .