Liu Yu glanced at the evolutionary history of the beast race and the demon race again, which were similar to those of humans, and they all wrote that it would end when they entered the clan commune. After watching it for a long time, Liu Yu didn't understand how humans evolved, so let's study it slowly in the future!

The other folders contained some information about this space and documents related to this underground building, whether it was useful or not, Liu Yu copied them first.

After copying the documents and materials in the computer, Liu Yu's eyes turned to the strange thing placed in the corner. What is this thing for? He's never seen it before.

Liu Yu looked at this thing carefully, it was about two meters high, three meters long, and one meter seven or eight wide, and it looked like a big wardrobe. But Liu Yu knew that it was definitely not a wardrobe. Because there is only a small door on its front, and the door is lifted upwards. It is also made of a special material, neither metal nor wood, and should be the same material as the case of a desk computer, a chemical compound collectively known as plastic. However, its plastic casing looks much stronger than the computer's case.

Another difference is that this thing is connected to a power supply, and it needs to use electrical energy to make it work. On the right-hand side of the small door there are two buttons, one green and one red. According to Liu Yu's experience, the green button is usually the start or turn on button, and the red button is the stop or close button.

After hesitating for a while, Liu Yu still pressed the green button. The small door slowly and silently opened, stopping at an angle of 120° to the shell.

What made Liu Yu feel strange was such a huge thing, but after the door was opened, the space inside was very small, and there was a device like a back chair, which could only accommodate one person to sit on it.

Although Liu Yu hadn't recognized what this thing was used for, he still decided to sit on it and try it, maybe there would be some unexpected gains.

The backrest chair is comfortable to sit on and fully ergonomic. The armrests, backrests, chair surfaces and footrests all fit his body, so he doesn't get tired even if he sits for a long time.

After Liu Yu sat down, the door slowly closed, and he suddenly fell into darkness. Immediately after that, the soft music sounded, and his spirit relaxed all at once. I closed my eyes, didn't think about anything in my head, just listened quietly, and I felt like I was back to nature. It was as if he was in the middle of a high mountain, sitting cross-legged next to a mountain spring, the mountain breeze blowing softly across his face, and the spring water was flowing happily, making a crisp and pleasant tinkling sound.

Soon Liu Yu was immersed in it, and he had forgotten where he was.

Suddenly, a picture of activity appeared in front of Liu Yu's eyes.

In the vastness of the universe, the Earth Star is slowly rotating, but what is it that appears below the Earth Star? A slender round rod stretches one end under the Earth Star, and the other end appears in the distance. This pole is at least fifty times as long as the Earth's star, is there such a long object? And there is something supporting the pole near the Earth's star, so that it cannot fall. The rod stretched out to the far end, and a large hand gripped it tightly and slowly pressed it down. At the end of the pole, the earth star is slowly lifted.

This picture kept repeating, Liu Yu didn't understand what it was trying to express at first, and after repeating it several times, Liu Yu gradually had some vague concepts in his mind. One hand, one fulcrum, the earth star, does it mean that give me a fulcrum, and I can pry the earth star? But the earth star is so big, is it possible for me to pry it?

Liu Yu kept thinking, and his hand involuntarily gestured, unconsciously overlapping with the big hand in the picture. There was a sensation that he was holding a pole in his hand, prying something hard. It was as if the earth star he saw in the picture was not heavy, and he could easily pry it up.

Looking at his palm suspiciously, Liu Yu was a little confused, was this just an illusion? Just when he was at a loss, a text appeared in the picture: "The principle of leverage, to balance the lever, the two moments acting on the lever (the product of the force and the force arm) must be equal in size." That is, the power × power arm = resistance × resistance arm, which is expressed algebraically as f1 · l1 = f 2 · l2. Among them, F1 represents power, L1 represents power arm, F2 represents resistance, and L2 represents resistance arm. From this, it can be concluded that in order to balance the lever, the power arm is several times that of the resistance arm, and the power is a fraction of the resistance. ”

After this explanation, Liu Yu has a deeper understanding of the picture. According to this equation, when the resistance and resistance arm are constant, the power arm becomes shorter, the required power should be larger, and vice versa, the power arm becomes longer, the required power becomes smaller.

In order to demonstrate this equation, Liu Yu held the pole closer to the earth.

Sure enough, when he pressed down again, he spent a little more force than he had just done. The closer he got to the direction of the Earth Star, the heavier Liu Yu felt that the Earth Star was getting heavier until he could no longer pry it. Holding the end of the rod again, it took almost no effort for him to pry it up again. With his own experience, Liu Yu finally fully understood the meaning of this picture and what the principle of leverage is.

After Liu Yu understood, as soon as he let go of the hand holding the round rod, the picture changed. This time it was a man sitting under an apple tree, unfortunate enough to be hit in the head by an apple. The man picked up the apple from the ground and watched it fall into deep thought.

At the same time that person was hit by an apple, Liu Yu also felt a pain on his head, as if an apple had also hit his head. Liu Yu rubbed the still sore spot on his head, and couldn't help muttering, this apple is really accurate! Although he complained a little, he still immediately turned his brain, thinking about what kind of principle this was deducing.

When Liu Yu didn't have a clue, the picture was still repeating, and the apple kept hitting the head of the person in the picture, and it also hurt on his head.

After being smashed many times, Liu Yu helplessly thought, why did the apple fall, how good it would be if it didn't fall, and my head wouldn't have been smashed so much! But this is the case on the Earth, no matter what kind of object it is, it will eventually fall to the ground, without exception, what is the reason for this?

Could it be that there is an invisible and untouchable force on the earth, and it is this force that binds us firmly to the surface of the earth? But we don't feel the existence of this force when we are on the earth?

The text appeared again when Liu Yu was halfway through thinking and a little ignorant.

"Gravitational force, any two particles are attracted to each other by a force in the direction of the concentric line. The magnitude of this gravitational force is proportional to the product of their masses and inversely proportional to the square of their distance, independent of the chemical nature or physical state of the two objects and the intermediary matter, and is expressed as: f=g・m1m2/(r・r). ”

With these words defining surnames, it is much easier for Liu Yu to understand again, gravity is no longer strange to him, and the application is not so jerky.

As soon as the picture turns, the image that appears this time is not so easy to understand.

Four-dimensional curved space-time, finite boundless universe, gravitational waves, gravitational mirrors, the Big Bang, black holes, space-time has been bent, and all kinds of intricate scenes make Liu Yu's head swell.

This time, the explanatory text appeared first, but it was these words that took Liu Yu a long time to roughly figure out its meaning.

This is a concept called general relativity, and it contains three principles: 1. The principle of general relativity, and all frames of reference are equivalent in describing the laws of nature. 2. The principle of invariance of the speed of light, the speed of light is constant in any frame of reference. 3. The principle of equivalence, the customary mass and the gravitational mass are completely equal.

This theory is extremely complex and involves the largest scope, until the end of the video, Liu Yu did not fully understand, but everything in the picture has been deeply imprinted in his mind, and it is not easy to forget it.

The picture is frozen there, it seems to let Liu Yu rest for a while, after all, allowing him to accept so much new knowledge in a short period of time is also a heavy burden on the brain.

When Liu Yu's brain stabilized, the picture changed again, but much faster than before, and it seemed that these theories were not so complicated.

The Three Laws of Motion, D'Alembert's Principle, Fluid Mechanics, Buoyancy, Thermodynamics, Mechanics of Materials, Dynamics, Engineering Mechanics, Structural Mechanics, Atomic Physics, Nuclear Physics, Photoelectric Effect, Electromagnetism, Quantum Mechanics, Electrodynamics...... The continuous emergence of new terms makes Liu Yu feel dizzying.

I don't know how long it took, the picture finally stopped changing, and Liu Yu also breathed a sigh of relief. So much knowledge was instilled into his brain at one time, and it was a little bigger, but fortunately, it was finally over. But if you think about it, this knowledge is still very useful to you, and many times, you only know how to make this thing, but you don't know what its principle is. Now that I have both practical work and theoretical support, I believe that I can do better.

Glancing at the time, Liu Yu didn't know if he didn't see it, he was startled, it didn't take long for him to enter this big box, a day has passed in a flash, and the time agreed before has passed, I don't know if they will be in a hurry, but fortunately, the distance is not too far, and it will be able to rush over in five minutes.

Glancing back at the star map on the wall again, Liu Yu hurriedly left the room.