Matter is required for sound to propagate, and such matter is called a medium in physics.

The transmission effect of sound in a single medium is better than that of a composite medium, mainly because of the reflection of the surface of the medium.

In addition, the essential phenomenon of sound is energy, and there will be a loss in the transmission of energy.

The degree of loss of sound in the wall and in the air is not the same.

The sound transmission effect of walls better than air refers to the infinity of energy, or the conclusion that ignores the loss of energy.

Chen Quan just wanted to stick his ear to the wall to listen to the situation in the room, and a lot of junior high school physics knowledge inexplicably appeared in his mind.

The effect of sound propagation in the composite medium is really not good, Chen Quan leaned his ear against the wall and did not hear any movement.

Suppose there are people in the rooms with these two opposite doors, what should he do now?

If your comrades-in-arms are acting with your comrades who have been training with you day and night, then you just need to give each other a look, and then you can attack.

But now that he is alone, Zhao Mengqing has no way to help at all, so he needs to break this situation by himself and win.

In order to ensure that there was no sound when the safety bolt was removed, Chen Quan pressed the safety bolt with his fingers to ensure that there was no sound.

If there were people in the room, it would be impossible to set a grenade trap on the door page.

Therefore, if you want to open the door, you can do a miracle and kick the door open, but Chen Quan did not do this.

If he kicked the door, his body would inevitably be exposed in the middle of the two doors, and maybe the people in the opposite room were secretly observing at the door.

Once he exposes himself, the people in the opposite room may immediately shoot black guns.

Insert the pistol back into the big one. Inside the quick-draw holster at the leg position, he squatted forward to the door of the room, and gently placed his left hand on the doorknob.

Touching the metal doorknob with his left hand, Chen Quan felt a hint of coolness.

When I touched the doorknob, the grenade safety in my right hand was also released, and the fuse was inside.

"Click—"

The doorknob is twisted and the door is opened.

When the door was opened enough to be thrown into the grenade, the right hand quickly skimmed the grenade in, and then lightly closed the door with a crisp clicking sound.

The whole set of actions to open the door and throw grenades to dodge and dodge, Chen Quan has practiced I don't know how many times.

At this moment, it is like the most basic martial arts movement of a martial arts master in actual combat, and the movements are as smooth as flowing water.

Before opening the door and throwing the grenade, Chen Quan also simulated the whole action in his mind, as well as the reaction of the other party if he found out that the door was opened.

Generally speaking, a person who squats in a room has only two corners to choose from, which are the two right-angled corners that extend along the door.

It could never be in the corner opposite the door, and if it was, it was not certain who would have been killed by whom.

In a right-angled corner, when you see the door being opened a crack, you will definitely not choose to shoot at the first time, you will definitely wait for the target to open all the doors, and only when you see the target, the person who squats will shoot.

Therefore, after Chen Quan opened the door, it was still relatively safe to gently push the door open, and the other party might still be waiting for him to continue to push the door.

But instead of pushing the door on, he threw a grenade in it like lightning and put it on.

When a grenade was thrown in, the person squatting in the room must have had his brain shut down and his face was full of confusion.

It's like a person who waits for a rabbit, originally wanted to squat a rabbit, but who knew that a wild wolf would squat.

Instead of leaning against the wall, Chen Quan held his gun in both hands, and pointed the muzzle of the gun at the door of the room opposite.

"Boom-"

Three seconds after the grenade was struck, it exploded in the room.

The loud sound came through the walls, and there was a clanging sound in the room, and the sound of objects falling into the water.

If the furnishings in the room were the same as the building in front of them, then the people in the room would surely die.

Because there was no shelter in the room, the fragments of the grenade explosion would definitely splash all over him, even if he was wearing a helmet and body armor, the lower half of his body would be covered with splinters.

And even if the grenade fragments do not completely destroy the person, the shock wave from the grenade explosion can cause fatal damage to the person.

"Knock knock!"

Fragments of the grenade erupted in a short period of time, and many of the fragments were nailed to the door, and the power was a little more powerful and directly penetrated the door panel.

Feeling that the walls were shaking and the ground was shaking, Chen Quan was half-squatting on the ground as steady as Mount Tai, and the muzzle of the gun was firmly pointed at the door of the opposite room.

……

Li Jian is not a newcomer, he is an old bird who has taken two badges, as long as he takes one more badge, he can obtain the ninth-level citizen authority.

Completely break away from the underground world and become a human living on the surface, and you will no longer have to fight hard in the underground world to survive.

While waiting for the prey to come to the door, Li Jian looked forward to a happy life as a ninth-level citizen in his heart.

The person in the opposite room was Li Jianze's teammate selected on the plane, and the other party was a newcomer, but he looked burly and a person with combat effectiveness, and he sneaked all the way from the front, and the other party behaved very well.

And the other party listens to his own words very much, and has no opinion on his own arrangement, Li Jian believes that as long as the two of them continue to use such an ambush method, the two of them will definitely win in the end.

Through the cat's eye on the door, Li Jian carefully observed the situation outside, and his ears did not relax, always listening to the movement outside.

Suddenly, Li Jian heard a slight sound of footsteps, and although the other party lowered the footsteps, he still heard it.

The reason why he has been able to live until now is that Li Jianze's sensitive ears have made a lot of contributions.

After hearing the sound of footsteps, he immediately prepared to fight, hoping that his teammates on the opposite side would be calm.

"Click!"

When he heard the click, Li Jian was shocked, he didn't see anyone in the cat's eye.

Moreover, this clicking sound is not from the door of his side, it is the sound of the opposite room being opened, so why can't there be any one in sight.

Don't rush!

Be steady!

Wait a minute!

The situation was somewhat unexpected by Li Jianze, but he suppressed the uneasiness in his heart and forced himself not to be impatient.

When he heard the click again, Li Jian looked out in the cat's eye on tiptoe, but unfortunately the cat's eye had a limited viewing angle, and he couldn't see anyone.

Just when Li Jian couldn't hold back and wanted to open the door to fight, an explosion suddenly came out of the opposite room.

At the same time, there were a lot of debris stuck to his door, making a thumping sound.

"What should I do?"

Li Jian leaned against the corner with a gun, staring at the door tightly, his forehead covered with sweat.