Rongguang's question seemed to open up Jose Alemani's chatterbox, or he was waiting for Rongguang to ask this question.

So he started his own... "performance".

"Ah, you can ask me this question. I have studied elevator balls specifically. Why do I study it? Because I found that this free kick method is too interesting. The football is almost motionless in the air and has no rotation at all. It is completely different from the free kick of Beckham with a very large arc... Logically speaking, a free kick is to bypass the wall of the man by arc and deceive the goalkeeper to achieve the goal. But why is there such a free kick? The football almost takes a straight line, flies forward, and then suddenly falls, as if something blocks the football down..."

"I thought it was a piece of luck from the players who played football."

Hearing this, Rongguang nodded. He thought so at the beginning. Cristiano Ronaldo was just lucky and confused. What's there to brag about?

"But I found that whether it is Cristiano Ronaldo, Juninho, or Pirlo, there have been such free kicks, which are not an isolated example. A person can get one by luck, but can so many people get one by luck? So I started to study this kind of free kick... I found that this free kick is definitely not a free kick. There are inevitable rules and connections from free throws to scoring."

Speaking of this, Alemani was a little excited. He waved his fists and looked excited as if he had discovered something new...

"I can even say that as long as you stick to the correct way of playing football, you can kick this kind of elevator ball that looks like it's a lucky one. Why do I dare say that? This is scientifically based..."

"Science?" Rongguang couldn't help but interrupt when he heard this, "What science is there to do with this free kick?"

Seeing Glory's expression so surprised, Alemani smiled.

"Of course, science," he said in a very affirmative tone. "Why does the elevator ball appear in such a state? This involves fluid mechanics. Because a football is a sphere that forms a streamlined contact with the surrounding air, causing turbulence or turbulence, that is, a rotating airflow. This means that the football will float in the air, left and right, or up and down. This involves a physics theory called the "Magnus effect," which means that when the rotation angular velocity vector of the rotating object does not coincide with the object's flight speed vector, a lateral force will be generated in the direction perpendicular to the plane composed of the rotation angular velocity vector and the translation velocity vector. This lateral force will cause the object's flight trajectory to deflect.

"Simply put, the arc ball we see is actually the embodiment of the Magnus effect. The effect of rotating objects being able to generate force in a horizontal direction is because the rotation of an object can drive the rotation of the surrounding fluid, causing the fluid velocity on one side of the object to increase and the fluid velocity on the other side to decrease. According to Bernoulli's theorem, increasing the fluid velocity will reduce the pressure, and reducing the fluid velocity will increase the pressure, which will lead to the pressure difference of the rotating object in the lateral direction and form a lateral force. At the same time, since the lateral force is perpendicular to the direction of the object's movement, this force mainly changes the direction of the flight speed, that is, forming a centripetal force in the movement of the object, thus causing the change of the flight direction of the object...

"This is the physical principle of arc ball. Let's take Beckham's arc ball as an example. You can see that the slower the ball reaches the goal and the faster the ball rotates. According to the Magnus effect, the difference in air pressure on both sides of the ball body causes the ball to deviate to the side opposite to the direction of travel.

"What about the elevator ball? It is not suitable for the Magnus effect. Because the ball's spin speed is very small, or even does not rotate, the foot force almost all acts on the kinetic energy required for the direction of progress. The moment the ball goes out, it obtains an extremely high speed. At the beginning, the ball will move forward in a straight line at a high speed, but as the air moves on the surface of the sphere in a streamlined manner, air pressure difference can be generated at any position of the ball, which directly causes the ball's movement line to float, left and right, or even up and down.

Juninho once scored a very famous free kick in the Ligue 1 League. The football changed direction twice in the air, and finally drew a B-shaped arc and drilled into the goal. If I remember correctly, the ball was 37.2 meters away from the goal, which was even further away than you practice now... I remember that the video of this goal was saved in my mobile phone..."

Speaking of this, Jose Alemani took out his cell phone, then found the goal video in the video, and took it out to play it for the two of them.

"You see, the football is almost unspinned in the air. The black blocks on the football have positional offsets, but this is not caused by rotation, and it just proves that the air puts pressure on the football from different directions... The goalkeeper therefore has no response to the ball at all..."

Then Alemani continued to talk endlessly, and spoke in an eloquent manner.

"I want to talk about why I think the elevator ball can be copied successfully, not caused by luck. Because there is only a reason, when I summarized that when Cristiano Ronaldo and Juninho kicked the elevator ball, I found that these two people had one thing in common, that is, they are both good at long-range shooting and can take direct free kicks from far away from the goal. Juninho has scored many free kicks very far away from the goal. What does this mean? It means that both of them have very strong feet. Yes, their feet are strong, and this is one of the conditions that must be met for kicking the elevator ball, that is, the batting power.

"The batting force must be large enough to allow the football to obtain the highest initial speed, so that the elevator ball can appear. Otherwise, you will not be able to kick the elevator ball at all. This is different from the arc ball. The arc ball does not require the initial speed, nor can it require the initial speed, because kicking the arc ball requires increasing the friction between the sneakers and the football, increasing the friction will reduce the speed. When kicking the elevator ball, it requires the shortest touch time, the shorter the speed, and the longer the touch time of the arc ball...

"Then why do you have to hit a strong ball to kick the elevator ball? Here I want to introduce a famous theory called "Carmen Vortex Street, Theory. This theory was proposed by the famous aerodynamic expert Von Carmen, so what is the vortex theory after him? It is that when the water and air flow are blocked by an object, the regular arrangement of vortexes formed behind the object is like a vortex forming a street, so it is called a vortex street... The vortex street effect will cause vibration to the object and even resonate with the object. In architecture, if it is serious, it will cause collapse accidents, such as the famous American Tacoma Bridge collapse accident...

"Similarly, because the football itself does not rotate, the football itself will not produce very strong lateral force. When the football passes through the air, when it encounters air resistance, the air will form a vortex behind it, which will cause the football to start to vibrate. This is also the reason why the football will rise and fall in the air, and go left and right in the air. When the vibration frequency is too large, a relatively large direction shift will occur, just like the amplitude of the Tacoma Bridge reaches nine meters under the influence of the vortex street, and the bridge deck collapses when it tilts to forty-five degrees.

"The basic formula of the vortex theory is very simple. F is equal to KV divided by B by 0. V can be regarded as the running speed of the sphere, the dam is the diameter of the sphere, and K is the number of Strauhars, which is related to the medium and the properties of the sphere, and is the frequency of shaking. From this formula, we can see that the faster the ball speed, the smaller the diameter of the sphere, the higher the frequency of the shaking of the football. The diameter of the football is fixed, and the number of Strauhars is relatively fixed. Then the only thing that can play a role is the speed of the ball, and the speed of the ball depends on the force you exert to the football... that is, the force of your shooting. The greater the shooting force, the higher the frequency of the football shaking after being influenced by the vortex theory in the air. This is why you must have enough strength to play an elevator ball. If the force is not strong and the ball speed is not fast, it will not be successful.

"This phenomenon can be calculated theoretically and is related to a ratio called a Reynolds number. The Reynolds number means that the ratio of the force given to the air to the viscous force of the football when you play a ball, and this number is called the Reynolds number. The elevator ball is related to the Reynolds number... I found through calculation and research that for a sphere that does not rotate, when the initial velocity is less than the end velocity, the sphere moves parabola, and when the initial velocity is much greater than the end velocity, the ball will fall sharply when it falls... that is, it forms an elevator ball. The basic formula for calculation is Newton's second law..."

Speaking of this, Alemani suddenly stopped his speech, and then asked Sun Fengyang, who was already stunned by the side: "Do you have any paper and pen?"

Sun Fengyang didn't react at all, so he mechanically handed him the paper and pen in his hand. The paper is actually the resume Alaimani just gave to Sun Fengyang.

Alaimani took it and didn't even read it. She turned over her resume and wrote it on the blank part on the opposite side.

He wrote down the formula of Newton's second law on paper, and kept talking in his mouth and his hands.

After writing the formula of Newton's second law, I wrote the second formula: "...Because it is an elevator ball, the sphere does not rotate, so the data of lateral force can be ignored. When only the air resistance is considered, and it is a large Reynolds number, which means that when the initial speed is very fast, this formula can be simplified to "

"... From this formula, we can finally get a final velocity Hc. Pay attention. The final velocity I am talking about is not the final velocity we understand in our usual sense, but the acceleration is equal to zero, that is, the speed when the velocity will not change again... It is a square form, which is related to the radius of the ball, the damping coefficient, and the air density... In short, we can calculate a final velocity... The relationship between this final velocity and the initial starting velocity determines the shape of the trajectory of the ball... That is, according to the formula just now, we can calculate the change of speed with time... If we make an integral of time for the speed, we can get the change of the distance over time, which is to give the trajectory of the football running..."

He began to draw XY axis diagrams on paper.

"...Looking at this arc, the initial speed is about 37 meters per second and the angle is 38 degrees. The calculated arc should be like this... Did you see it? A typical elevator ball running route. At the beginning it was a relatively slow slope, and then it was very steep down... So, there are rules for kicking elevator balls. As long as you follow this rule, the chance of success will be greater than if you don't follow the rules. Uh, I don't know what I said... Have you explained it clearly?"

Speaking with great enthusiasm, Alemani raised his head from his calculation formula and looked at the already stunned chicken, like a petrified Rongguang and Sun Fengyang...
Chapter completed!