"Wait, I'll go to the toilet first and then come back to give you an answer, Guo Chun, let's go."

Bao Guowei did not refuse An Shuzhen's question, which made people think that he was unkind.

"yes, okay."

Ahn Sook-jin nodded, turned her head and continued to think about the question.

……

"Why, this school is like being sick, I have to take classes for so long in the morning, and when I came here today, I drank a bowl of sour plum soup, and I was suffocated to death after a class."

After walking out of the classroom, Guo Chuncai scolded and complained, and also swore words.

"Then you will drink less water in the morning, you have already passed the grade, are you still not suitable for this routine?"

"If it weren't for the surname Song in this class, I would have raised my hand and shouted to go to the toilet, can I wait until now?

And it's all been a holiday, and my schedule has long been changed, and I usually have nothing to do at home to read, read the newspaper, and there are people waiting, and then find someone to play basketball, and you can also go shopping...... Anyway, I don't know how much happier I am than going to school. ”

The two were chatting, and Bao Guowei found that there was an extra shadow on the wall next to him, and he followed the two of them step by step, and he didn't need to look back to know that it was Chen Jinhua.

Chen Jinhua yawned, and followed the two weakly, he was still a little sleepy, but Guo Chun couldn't help but accompany him when he came out of the classroom, what if Guo Chun felt that he had changed his mind:

"Guo Chun, why don't we go to Songhe Tower for dinner tonight, our Himalayan team members haven't been to Songhe Tower for dinner for a long time."

Guo Chun ignored him, if Bao Guowei said this, he could still consider agreeing, Chen Jinhua only treated him as a fart when he spoke.

Chen Jinhua is always very persistent about the Pine Crane Tower, Bao Guowei has only known him for a day, and he has heard him mention the Pine Crane Tower several times, and he doesn't know what is attractive there.

Just after class, the students love to come out and move, there are already many students in the aisle, just a female classmate walked by, wearing a pink scarf, holding a book in her hand, looking good.

When Guo Chun saw the female classmate, he couldn't help but want to tease, he jumped up gently, made a shooting motion, and whistled at her, the girl immediately blushed and fled.

Seeing this, Bao Guowei inadvertently distanced himself from Guo Chun: this kind of behavior was so embarrassing that he was ashamed to be with Guo Chun's classmates.

There are toilets on each floor of the school building, and the farthest distance from the classroom is only a few dozen steps.

However, the morning is a time when it is easy to have diarrhea, especially in autumn, when it is cold, and now it is almost winter......

The three of them escaped from it almost with their noses covered with their clothes, and the smell was insulting.

"I don't come here again, I still have to go to the toilet for teachers, there are fewer people, and it's much cleaner."

Probably because he had been holding his breath for a long time, Guo Chun was still a little slow when he spoke, and he was still panting when he spoke.

……

Back in his seat, Bao Guowei found that An Shuzhen was still thinking seriously about which question, took out a pencil, and poked her with the back of his head.

"Which question? Just ask. ”

An Shuzhen turned her head, pointed to the handout and said, "That's it, it feels so difficult." ”

At the end of the reverse side of the handout, this question is an extended question, which is still a picture of the problem.

Just by looking at the picture, Bao Guowei knew that there was a problem with this question, and according to the teaching progress, this topic appeared a little early:

The mass M = 1 kg, the long wooden board with a length of L is stationary on the horizontal plane, and a small block with a mass of m = 1 kg (which can be regarded as a particle point) is placed at the left end, the dynamic friction factor between the small object and the wooden board is μ=0.3, and the dynamic friction factor between the wooden board and the horizontal plane is μ′=0.1.

Give the small block a horizontal pull force of F=6N to the right, so that the small block accelerates to the right relative to the plank, and the gravitational acceleration g=10 m/s squared. Find the acceleration of small blocks and planks. (The dynamic friction factor is the ratio of sliding friction to positive pressure)

After reading the whole question, Bao Guowei frowned, this question is a bit complicated at first glance, and it is estimated that it is as difficult as the ordinary physics questions in the college entrance examination in later generations.

It's only the first day of school, and Teacher Song has this kind of question, which is really a bit outrageous.

The only difficulty in this question is the introduction of friction, which is relatively difficult to understand.

Not to mention that this problem is essentially three objects in a frictional motion in an inertial frame, which is still more troublesome to analyze.

Not only is the topic a little overclassed, but the second question is also a bit poisonous, and those who don't have enough understanding of Niu Er's law can easily substitute small blocks and planks as a whole into Niu Er's formula.

Bao Guowei frowned and thought for a while, took out his outline, took out a pencil, and wrote and drew on it, his pen was very fast, and after a while, the entire outline was full.

An Shuzhen sat opposite, unable to see what Bao Guowei was writing, Guo Chun, who was sitting next to him, looked at it curiously, the bunch of letters in front of him was simply dizzy, and his eyes when he looked at Bao Guowei suddenly became like looking at a monster.

"First of all, the gravitational acceleration g=10m/s square means that the object is subjected to gravity of 10N/KG, I won't tell you how to derive this result, you just remember it, and the teacher will definitely talk about it later."

Pointing to the conditions on the topic, Bao Guowei said to An Shuzhen.

It's not that Bao Guowei is unwilling to teach her, just the derivation of the acceleration unit is meters per square second, maybe it can make her dizzy, which involves several letter unit transformations, and if you are not proficient in the formula, you will definitely not be able to understand it.

An Shuzhen glanced at Bao Guowei and nodded, feeling a little puzzled in her heart.

"Since the teacher didn't talk about it...... How did he know? If he is self-taught, then he is too powerful! ”

An Shu thought to herself in her heart, and listened quietly to Bao Guowei's next sentence:

"That is to say, the positive pressure of the small block on the long wooden board is 10N, and the dynamic friction factor is 0.3, and considering the tensile force given to the small block horizontally to the right by 6N, which is greater than the sliding friction, then the friction of the small object on the long wooden board is 3N, and the direction of friction is opposite to the direction of its movement, understand?"

Bao Guowei took out a pencil and pointed to the small wooden block, and drew an arrow to the right on the small wooden block, writing 6N, marking F, and drawing an arrow to the left under the small wooden block, writing 3N marking f.

There is an old saying that if you are undecided, first build a Cartesian coordinate system, and then talk about a wave of force analysis.

Problems that are not very good can often be solved directly and violently after analyzing the stress situation.

Up to the sun and the moon, down to the atoms and electrons, this kind of operation is very good, and every physics teacher in later generations will teach it, and it will run through almost the entire high school physics career of students.

An Shuzhen looked at the picture drawn by Bao Guowei seriously, frowned slightly, she thought about Bao Guowei's words seriously, and thought for a while before figuring out the joints.

"I ...... Figured it out. ”

An Shuzhen said softly, her words made Bao Guowei a little surprised.

Bao Guowei thought that An Shu really couldn't understand it, and this question could be said to be a hellish difficulty for students who had only taken one big class.

It seems that this female classmate is at least clear-headed, and she still has some talent in physics.

After all, Instructor Song's big class can be called an outline of rapid instillation of knowledge points, and An Shuzhen can still achieve a preliminary understanding of it, which is already more than the vast majority of people.

As for Guo Chun next to him, he was already stunned, and after hearing An Shuzhen say that he understood, he felt that his self-confidence had been hit, and he felt that his whole person had become a little unconfident.

Bao Guowei then spoke:

"Okay, now that the force has been analyzed, then it is time to calculate the resultant force, the small block is subjected to: tensile force, friction force, gravity, support force, calculate it, relying on Newton's second law formula to solve the first question, you try to solve it."

An Shuzhen is still a little unfamiliar with formulas, after all, Instructor Song has taught too many things in this class, so she can only look through the Gewu book and find formulas.

"On the horizontal plane, F is equal to the tensile force minus the sliding friction force, and the two forces are balanced in the vertical direction...... Three meters per second? ”

An Shuzhen said cautiously, her face full of expectation, hoping that Bao Guowei would say that her answer was correct.

However, her answer was not entirely correct, the values were correct, and the units were wrong.

"If this little question is four points, at least one point will be deducted from you, the unit of acceleration is meters per square second, and the unit of velocity is meters per second, why is it meters per square second, this unit involves the definition of acceleration, and the instructor will definitely take you to derive."

Bao Guowei said mercilessly, but this already made An Shuzhen very happy: he was just the wrong unit, and the value was correct.

"Let's move on to the second question, the force is mutual, the frictional force is the force that hinders the movement of the object, who is hindering the small wooden block?"

"Long planks."

"Yes, since the long wooden board hinders the small wooden block, and the small block is subjected to the friction of the three oxen to the left, is it possible to conclude that the long plank will also be subject to the friction of the three oxen to the right according to the law of the three oxes?"

Bao Guowei started to mark the arrows on the long wooden board again.

“…… Right. ”

"There are four forces on a long plank: gravity, support, friction on the ground by a small piece of wood...... The analysis is actually almost at this point, and there is one thing to pay attention to, that is, do not treat two objects as a whole, because ......"

When Bao Guowei talked about this, he entered the state, and began to talk endlessly about the easy points of error, and as he spoke, several classmates around him were also attracted by him, and listened dumbfounded as Bao Guowei spoke a language they didn't understand.

"Do you understand?"

“……”

This time, An Shuzhen didn't reply, just frowned, thought seriously, and looked at Bao Guowei's handouts, which seemed to be getting into the tip of the horns.

"Bao Guowei, I've had a lot of trouble listening to these things, how do you know so much?"

An Shuzhen thought for a while and didn't understand, she really couldn't help the curiosity in her heart, and asked Bao Guowei.

"Because I'm a genius, I can read a few books at random, and I can integrate the knowledge in them, and the world of genius is so unpretentious.

It's already good that you can understand the first question, and it's appreciated, come on. ”

Bao Guowei began to brag to himself, and subconsciously wanted to pat An Shuzhen on the shoulder to cheer her up, but his hand was just about to fall and retracted.

almost committed a taboo, the Republic of China is different from the later generations, and a girl's shoulder can't be patted casually.