What is a banana ball
If you are a football fan, you must have seen this wonderful scene: when a direct free kick is served near the opponent's goal, five or six players of the defensive side line up in a "human wall" in an attempt to block the route leading to the goal, but the penalty taker of the attacking side did not hesitate, slowly stepped forward, put the ball in the right position, and then made a sharp shot, only to see the ball bypass the "human wall" and fly out of bounds.
This is a pretty magical banana ball. Because the path of the ball is curved, like a banana, it is named "banana ball".
The secret of banana ball
We know that when the ball flies in the air, if it not only moves forward, but also rotates continuously, because the air has certain adhesiveness, when the ball rotates, the air rubs against the spherical surface, and the rotating ball drives the surrounding air layer to rotate together. If the ball moves to the left in the horizontal direction and rotates clockwise around the axis perpendicular to the paper, the airflow not only flows to the right relative to the ball, but also the surrounding air circulation layer driven by the ball rotation rotates clockwise. In this way, the air speed above the ball rotates in addition to translation to the right, and the two directions are the same; Below the ball, the translation speed (to the right) is opposite to the rotation speed (to the left), so its approaching speed is less than the air above the ball.
According to Bernoulli theorem of fluid mechanics, the pressure on the higher speed side is less than that on the lower speed side, so the pressure above the ball is less than that below the ball. The resultant force of air pressure on the ball is different from top to bottom, and the total resultant force is upward. If the ball rotates so fast that the upward resultant force of air on the ball is greater than the weight of the ball, the ball will be subjected to a vertical upward resultant force in the process of moving forward, so that the ball will bend forward and turn upward in the process of moving horizontally to the left. To make the ball rotate left and right, just make the ball rotate around the vertical axis. It seems that the key is the athlete's footwork when he touches the ball, that is, not only to make the ball move forward, but also to make the ball rotate quickly. Different rotation directions will make the ball rotate differently. This requires athletes' hard training and a set of skillful footwork, and only hard training can achieve perfection. In fact, there are more than "banana balls" in football. Table tennis, volleyball, tennis and so on. They all use rotating technology to create all kinds of erratic mysterious strange balls, such as curling balls in table tennis and floating balls in volleyball, which are all created according to this principle. The principle of banana ball is based on aerodynamics. That is, the greater the relative velocity between the sphere and the air, the greater the force on the sphere and the greater the curvature of the sphere. Suppose you look down from directly above the ball (the line of sight is perpendicular to the ground), the instantaneous direction of the ball's trajectory is perpendicular to your line of sight, and the ball rotates counterclockwise. The relative friction velocity between the right side of the ball and the air is greater than that of the left side, so the direction of the ball will shift to the left. The greater the relative friction velocity, the greater the offset of the ball, that is, the greater the radian. This is the radian, and here is the height. Suppose you look at the ball from the front (the line of sight is parallel to the ground), and the instantaneous direction of the ball trajectory is perpendicular to your left. If the ball rotates clockwise, the friction velocity of the lower part of the ball relative to the air is greater than that of the upper part, and the ball falls more slowly. It's easier to bypass the wall (but the ball is slow, giving the goalkeeper too much time to react). On the contrary, the faster the ball falls, it is not easy to bypass the wall (but bypassing is a threat).
An active free kick player in world football.
Beckham, perhaps the most expensive right foot in Europe, is good at taking the penalty with the instep, and the ball flies to the opponent's corner in a pleasing internal rotation arc. Beckham has received regular training since he was a child, and his strokes and styles look very simple and orthodox. In order to improve the speed, he must twist his whole body and tilt his body completely to increase the internal rotation speed of the ball, so it usually gives people the feeling of lightning speed, which is why we have our common Bayesian free kick posture. Goalkeepers always want to know why they often judge the right direction but are still half a beat slow. But scientific data tells us that Beckham's free kick shooting speed is above 1 10 km every time. Now people call his curved ball with rapid rotation and accurate landing point "Bayesian radian", which is a simple but deadly effective weapon in attack. Former free kick master Platini once commented: "Beckham is definitely the best right-footed free kick player in Europe. If he unfortunately meets his team, don't give him any chance near his restricted area. "
Classic replay: 2002 World Cup qualifier, World War I Greece, last minute, the most wonderful kick, worth-1 100 million!
Ronaldinho is the world's number one star. Ronaldinho's free kick speed and arc are perfectly combined. In gremio, Paris and Barcelona, people have become accustomed to him humiliating the opposing goalkeeper with accurate half-high balls again and again. In the first year of joining the Rossoneri, he helped Barcelona return to the top with a goal of 15, and then won the title of World Footballer of the Year. His position in the national team has also soared. Now, unless it is 35 meters away, Ronaldinho has basically arranged all the positioning balls in the front of the restricted area, and the accuracy of his feet has also been well received by all parties. What is even more frightening is that the Brazilian king often does not need a run-up, but can complete all the processes with calf strength, so that the opposing goalkeeper can't judge the path of the ball. Although the team lost in that century war, Ronaldinho's free kick that bypassed the human wall made casillas, the first goalkeeper in La Liga, have no time to react.
Classic replay: Barcelona played against Royal Society at home in 2004. Until the 90th minute, Barcelona was still 0- 1 behind. Ronaldinho himself got a free kick in front of the penalty area. Although it was a little close, the Brazilian's free kick went straight to the lower left corner. The whole Nou Camp is crazy, not only to surpass the old rival Real Madrid in the standings, but also to suppress the excitement of his new king.
Roberto carlos, a small Brazilian Carlos, has a magical left foot. His upper limbs are short, his thighs are thick and powerful, and his calves swing concealed and quickly. He relied on powerful explosive force to punish free kicks. Opponents will never dare to foul easily outside the penalty area, because people know that that kind of recreational free kick is almost the same as being awarded a penalty. In addition, Carlos seems to be learning the principle of grafting ball in table tennis and snooker. Sometimes people feel that he deliberately calculated that the ball hit the goal through the collision of a third party in the human wall, so that he can directly test the rebound of the "target" without bothering to avoid the blocking of the "human wall". That bloody and domineering free kick is the gold-lettered signboard that this pocket gold left foot dominates the world football.
Classic replay: 1997 the 40-meter-long exo missile scored by the French team in the French four-nation football invitational tournament. After the game, French newspapers could not explain how Carlos turned the ball flying to the corner flag and scored a goal, so they had to ridicule and explain from the perspective of physics that "according to Newton's third law, when an object moves to the right, the wind speed generated by the repulsive force of the object will react on it."
Juninho Lyon Jr. won four incredible league titles in a row, and Juninho Jr. was the biggest contributor. Since joining Bamba Ligue 1, he has been good at strict organization and scheduling, and he has become the leading midfielder in France. At the same time, the Brazilian is also a top free kick player. According to statistics, every time he made seven penalty kicks, he bypassed the human wall and scored the goal. This probability is terrible. Kahn should be the person who knows the Brazilian power best. In the Champions League, the German goalkeeper was humiliated by Juninho's free kick. Even Asunció n Pucao and Carlos, recognized as top set-pieces players, admitted that their compatriots' unique skills were above themselves. Juninho's free kick stunt relies on talent, feeling and hard practice. It has always been his fixed habit to practice at least 20 free kicks after each training. Although he is still a supporting role in the national team, he is the absolute king in France, which advocates technical football.
Classic replay: Juninho's 35-yard free kick in the Champions League directly broke the door guarded by Bremen goalkeeper Lenke. This is a classic handed down from generation to generation and is recognized as one of the best goals in the last Champions League, comparable to the two magical goals of Ronaldinho of Chelsea and Garcia of Juventus.
Mikhailovich's free kick volleying from the outside of the instep of his left foot is Miha's specialty, and the direct free kick shooting within 40 meters from the goal is impeccable. Miha's free kick is a perfect work of art with sharp angle and strong rotation. Moreover, when he takes a free kick, he usually tries to use his calf as much as possible, and his thigh swings very little, so the goalkeeper can't judge the path of the ball, so the gods and ghosts are unpredictable. "We have asked UEFA if we can use two goalkeepers when mikhailovich takes a free kick. I think this is the only way to stop him. " When Leverkusen was in the same group as Lazio in the Champions League, Dom, the team's meritorious coach, said to himself. Misha's free kick is unique in European football. He is the holder of Apennine's direct positioning record. Even we think that Miha's first impression is a registered trademark free kick, and vice versa, which is almost a conditioned reflex. His purpose of "beating blood to seal his throat" makes his opponent feel scared.
Classic replay: 1999, mikhailovich scored three goals from a free kick against Sampdoria. Created an unprecedented historic feat, and no one came after it.