Glory's question seemed to open José Alemani's conversation, or he had been waiting for Glory to ask him.

So he began his own ...... "acting".

"Ah, that's the right question! I've specialized in elevator balls. Why research? Because I found it so interesting that the ball was almost motionless in the air, with no spin of its own, unlike Beckham's free-kicks...... It stands to reason that a free kick is to rely on an arc to go around the human wall and deceive the goalkeeper, so as to achieve the purpose of scoring a goal. But why are there such free-kicks? The soccer ball flies forward almost in a straight line, and then it suddenly falls, as if something is blocking the ball......"

"At first I thought it was the luck of the players."

Hearing this, Rongguang also nodded, he also thought so at the beginning, Cristiano Ronaldo was just lucky, and he was in it, what is there to brag about?

'But what I found was that Cristiano Ronaldo, or Juninho, or Andrea Pirlo had all scored from free-kicks like this, and it wasn't an isolated example. One person can be lucky enough to get into one, but can so many people be able to get in by luck? So I started working on this kind of free-kick...... I found that this free kick was definitely not a lucky one, there is an inevitable law and connection between the penalty kick and the goal! ”

Speaking of this, Alemani himself was a little excited, and he waved his fist as if he had discovered some new element......

"I would even go so far as to say that if you stick to the right way you kick the ball, you can kick this kind of elevator ball that looks like a stroke of luck! Why do I dare to say that? This is scientifically grounded......"

"Science?" Rongguang couldn't help but interject when he heard this, what kind of science is there in this free kick?

Seeing Rongguang's surprised expression, Alemani smiled.

"Of course, science!" He said in a very affirmative tone. "Why is the elevator ball in such a state? This brings us to fluid science. Because the football is a sphere, it will form a streamlined contact with the surrounding air, which will cause turbulence or turbulence, that is, a rotating air flow, which is that the football will be erratic in the air, left and right, or up and down. This involves a physics theory called the 'Magnus effect', which states that when the rotational angular velocity vector of a rotating object does not coincide with the object's flight velocity vector, a transverse force will be generated in the direction perpendicular to the plane composed of the rotational angular velocity vector and the translational velocity vector. This transverse force will deflect the object's flight trajectory.

"To put it simply, the curling ball we see is actually the embodiment of the Magnus effect. The force that can be generated laterally by rotating an object is that the rotation of the object can drive the surrounding fluid to rotate, so that the fluid velocity on one side of the object increases and the fluid velocity on the other side decreases. According to Bernoulli's theorem, the increase of fluid velocity decreases the conductive pressure, and the decrease of fluid velocity increases the conductive pressure, which leads to the transverse pressure difference of the rotating object and forms a transverse force. At the same time, since the transverse force is perpendicular to the direction of motion of the object, this force mainly changes the direction of flight speed, that is, forms the centripetal force in the motion of the object, and thus leads to the change of the direction of flight of the object......

"This is the physics of the curveball, we take Beckham's curveball as an example, we can see that the ball is slower the ball reaches the goal, the faster the ball spins itself, according to the Magnus effect, the difference in air pressure on both sides of the ball body leads the ball to the side where the angular velocity direction is opposite to the direction of travel.

"And what about the elevator ball? It doesn't apply to the Magnus effect. Because the spin speed of the ball body is very small, or even does not rotate, the foot force is almost all acting on the kinetic energy required in the direction of progress, the moment the football goes out, it obtains a very high speed, at the beginning the ball will move forward in a straight line at high speed, but with the air action on the surface of the streamlined sphere, the ball can produce a pressure difference at any position, and the direct guide to the ball movement line is erratic, left and right, and even up and down.

Juninho Jr. once scored a famous free-kick in Ligue 1, where the ball changed direction twice in the air and finally drew an S-shaped arc into the goal. If I'm not mistaken, the ball was 37.2 meters from the goal, which is farther than the distance you are practicing now...... I remember having a video of the goal saved on my phone......"

With that, José Alemani took out his mobile phone and found the goal video in the video and showed it to the two of them.

"You see, football is almost non-spinning in the air. The black patches on the soccer ball have a positional shift, but this is not due to rotation, but just a testament to the fact that air is putting pressure on the ball from different directions...... The goalkeeper did not react to the ball at all......"

Then Alemani continued to gush endlessly.

"Here I would like to say why I think the elevator ball can be replicated successfully, not by luck. Because there is only a reason, when I summarized Cristiano Ronaldo and Juninho Jr. kicking the elevator ball, I found that these two have one thing in common, that is, they are both good at long-range shots, and they can both take direct free-kicks from a long distance from the goal, and Juninho Jr. has scored many free-kicks very far from the goal. What does this mean? It shows that both of them have very strong feet, yes, strong feet, which is one of the conditions that must be met to kick the elevator ball, that is, the power of hitting the ball.

"The ball has to be strong enough for the ball to get the highest initial velocity so that there can be a lift ball, otherwise you won't be able to kick the lift ball at all. This is different from the curveball, which does not require initial velocity, and cannot require initial velocity, because kicking the curling ball increases the friction between the boot and the football, and increasing the friction will reduce the speed. Kicking the elevator ball requires the contact time to be as short as possible, the shorter the speed, the faster the speed, and the longer the touch time of the curve ball......

"So why do you have to hit the ball hard to kick the elevator ball? Here I would like to introduce a well-known theory called the 'Carmen vortex street' theory, which was proposed by the famous aerodynamics expert von Kármen, so it is named after him...... What is the Vortex Street Theory? When the flow of water and air is blocked by an object, a whirlpool formed behind the object is arranged in a regular manner, which looks like a whirlpool forming a street, so it is called a whirlpool street...... The vortex effect will cause vibrations to the object, and even cause resonance between the object and the object. In terms of architecture, Yan zhòng's words will cause collapse accidents, such as the famous Tacoma Bridge collapse in the United States......

"Similarly, the elevator ball kicked out, because the football itself does not rotate, so the football itself will not produce a very strong lateral force, when the football passes through the air, it encounters air resistance, and the air will form a vortex behind it, which will cause the football to start vibrating. That's why football goes up and down in the air, left and right. When the vibration frequency is too large, a relatively large shift in the direction will occur, just as the Tacoma Bridge collapsed when the amplitude reached nine meters under the influence of the vortex street and the bridge deck was tilted to 45 degrees.

"The basic formula of vortex theory is very simple, that is, F is equal to KV divided by D (f=KV/d), V can be regarded as the speed of the sphere, d is the diameter of the sphere, K is the Strauhar number, which is related to the medium and fluid properties of the sphere, and f is the frequency of the sloshing. From this formula, we can see that the faster the ball speed, the smaller the diameter of the ball, and the higher the frequency of the ball shaking. The diameter of the soccer ball is fixed, and the Strauhar number is relatively fixed, so the only thing that can make a difference is the speed of the ball, which depends on the force you exert on the ball...... That is, the power of your shot. The greater the power of the shot, the more often the ball will shake in the air after being affected by the vortex theory. This is why you have to be strong enough to kick the elevator ball, and if the power is not strong and the ball speed is not fast, it will not be successful.

"This phenomenon can be calculated theoretically, and it is related to a ratio called the Reynolds number. The Reynolds number is the ratio of the force you give to a ball and the viscous force that the air gives to the ball, and this number is called the Reynolds number. The elevator ball is related to the Reynolds number...... I found that for a non-rotating sphere, when the initial velocity is less than the terminal velocity, the sphere is in a parabolic motion, and when the initial velocity is much greater than the terminal velocity, the ball will fall sharply...... That is, the formation of the elevator ball. The basic formula for the calculation is Newton's second law......"

Speaking of this, Alemani suddenly stopped his speech, and then asked Sun Fengyang, who was already stunned next to him: "Do you have paper and pen?" ”

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

Alemani took it, didn't even look at it, and directly turned over his resume and wrote it in the blank part on the back.

He wrote down the formula for Newton's second law on a piece of paper, and kept talking about it with his mouth and hands.

After writing the formula for Newton's second law, I wrote down the second formula: "...... Because it is an elevator ball, the sphere does not rotate, so the number of lateral force jù is negligible, and in the case of only considering air resistance, and it is a large Reynolds number, that is, when the initial speed is very fast, this formula can be simplified to ......"

“…… From this formula, we can finally get a final velocity U∞, note that the final velocity I am talking about is not the final velocity in our ordinary sense, but the velocity when the acceleration is equal to zero, that is, the velocity will not change again...... It is a square form that has a relationship with the radius of the ball, the damping coefficient, and the density of the air...... All in all, 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 in velocity over time...... And if you do an integral of time for speed, you can get the change of distance over time, that is, you can give the trajectory of the football ......"

He began to draw a diagram of the XY axis on paper.

“…… Looking at this arc, the initial velocity is about thirty-seven meters per second, and the angle is thirty-eight degrees, and the calculated arc should look like this...... See? The running route of a typical elevator ball. It starts with a gentle climb and then descends very steeply...... So, there are rules for kicking elevator ball, and as long as you follow this rule, the odds of success will be greater than if you don't follow the rules! Uh, don't know what I say...... Did you make it clear? ”

Speaking of this with great interest, Alemani raised his head from his calculation formula, looked at the glory who was already stunned, as if petrified, and Sun Fengyang said......