Chapter 547: Teacher Xus small class has started (Part 2)
"..."'
in the house.
Zheng Tao finished speaking.
The interest group scene, which had not had many noisy conversations in the first place, became quiet again.
It is clear.
After all, this is everyone's first gathering, and most of the members are quite restrained and don't dare to speak easily.
See this situation.
Zheng Tao didn't feel disappointed or surprised, but smiled at everyone as usual and said:
"Comrades, we are all old acquaintances who have known each other for a while, so there is no need for such an inconvenience, right?"
"The purpose of our group is that everyone can speak freely, regardless of hierarchy, just like we did in school, and there won't be too much psychological pressure."
"How about it? Is there any comrade who volunteers to fire the first shot?"
Say it.
Zheng Tao turned his head and silently winked at a girl sitting in the corner.
This was a sitter arranged by Zheng Tao in advance. In order to prevent the sitter from being left out, Zheng Tao specially chose a lesbian.
But just as this guy was about to appear.
Diagonally opposite Zheng Tao's seat.
A boy who wore glasses and had a single ponytail on the back of his head, who looked very artistic, raised his hand first:
"Comrade Zheng Tao, then I will shamelessly come here as a stepping stone to give everyone a start."
Zheng Tao was slightly startled, then his face brightened:
"No problem, no problem, Comrade Fang Zhong, if you have any questions, just ask. Let's work together."
to be honest.
Zheng Tao was indeed a little surprised.
At first, he thought that someone would take the bait only if the shill he arranged came on stage, but to his surprise, someone actually jumped out on his own initiative.
It's like a fisherman preparing to buy fish at the market, but a fish automatically jumps into the fishing net.
This is really...
Very good.
As for the boy who spoke, Zheng Tao also knew him.
This person's name is Fang Zhong, and he graduated from the famous South China Institute of Technology...which later became South China University of Technology.
In addition to his high academic qualifications, Fang Zhong is also very good at the mouth organ. Every time the educated youth at the base hold various gatherings, the organizers will basically ask him to help with the accompaniment.
Then a group of male singles sit by the campfire, imagining the beauty of love in the melodious harmonium, and then continue to be single the next day...
The sight returns to reality.
I don’t know if it’s due to the long-term ‘performance’ experience.
At this time, Fang Zhong looked very calm under the gaze of everyone, quite like a social cow.
He adjusted his glasses, coughed slightly, and said:
"Comrades, the issue I want to share with you is actually a phenomenon I discovered at work a few days ago."
"Everyone must know that I am currently assigned to work in the literary and artistic sideline team of the base. My main job is to help the team."
"Recently, isn't the sideline team preparing the stage for the factory's stage commendation meeting? In addition to banners, there will also be several rows of small balloons hanging on the stage to liven up the atmosphere."
"About noon three days ago, I suddenly discovered something when I was blowing up the balloon. It was more difficult to blow up the balloon at the beginning, but it became easier and easier later on."
Speaking of which.
Fang Zhong couldn't help but rub his temples and sighed:
"I am a person who likes to be more serious. When I encountered this situation, I suddenly wanted to understand its principle."
"So I have been thinking about this issue in the past few days. What is the reason or principle that leads to this situation?"
"But after thinking about it over and over again, I couldn't figure out the reason in the end."
"...."
Fang Zhong's reputation and popularity among the base's youth circles are very good, otherwise he would not have the confidence to say such things [I believe everyone knows it].
In addition, the question he asked is indeed somewhat new, and it is a small detail that many people don't pay attention to at ordinary times.
So it's very fast.
There were low voices of discussion in the room.
After a while.
A tall, thin boy with a sallow complexion and a malnourished look raised his hand:
"Comrade Fang Zhong, could this be your imagination?"
"After all, according to the gas pressure formula pv=nrt, it seems that the situation you mentioned should not occur."
I heard these words from the tall and thin boy.
Several people at the scene also nodded in agreement.
The gas pressure formula pv=nrt is a concept that is very popular even in this era - relatively speaking at the college student level.
It is not difficult to judge from the formula that the more gas the balloon has, the more difficult it will be to blow it up.
However, Fang Zhong was silent for a moment after hearing this, and shook his head firmly:
"It shouldn't be my misunderstanding, because I asked several comrades who blew up balloons together, and everyone said this was the case."
"That is to say, the bigger the balloon is, the easier it will be to blow it up."
Say it.
Fang Zhong also took out a small uninflated balloon from his body and threw it accurately in front of the boy:
"Comrade, this is the little balloon my team leader gave me after I worked overtime yesterday. You can try blowing it up."
"...."
The tall and thin boy looked up at Fang Zhong, picked up the small balloon, put it to his mouth and blew it up.
inhale,
exhale,
stop......
The balloon soon began to slowly grow in size.
And just when the balloon swelled to the size of a grapefruit, a hint of astonishment suddenly appeared in the tall and thin boy's eyes.
Then he continued to blow it twice, and the balloon finally became about the size of a basketball.
Then the tall and thin boy slowly let go of his mouth, held the balloon with both hands, and let the gas inside puff out.
See this situation.
Fang Zhong couldn't help but ask him:
"How is it? Is what I said correct?"
The tall and thin boy nodded silently.
During his previous attempt, what Fang Zhong mentioned did indeed occur.
That is to say, there is obvious resistance at the beginning, but the larger the balloon, the easier it becomes.
Then several boys around him also tried it one after another, and they all found that the resistance of the balloon at the beginning was much higher than that at the middle and later stages.
This was obviously a counter-intuitive situation, so the young intellectuals at the scene immediately had a desire to discuss it.
"Well...I have a guess."
The person who raised his hand this time was a future boss, the Yang Fujia whom Xu Yun had recognized before, a well-known atomic energy scientist in the future:
"Could it be that the wall layer of the balloon is thicker and relatively compact when it is not inflated, and becomes thinner and looser after it is inflated, so it becomes easier the more it is inflated?"
Hear this.
Zhou Shaoping, who was sitting opposite him, thought for a moment and quickly shook his head:
"Lao Yang, your explanation is too life-like and far from the essence of physics."
"I think if this phenomenon does exist, then it must have a deeper explanation. After all, everything is scientific."
Xu Yun glanced at Zhou Shaoping.
During this period, due to equipment accuracy issues, the physics community's understanding of the microscopic field had not yet developed to the next level.
Therefore, most physicists firmly believe that everything can be answered through existing theories - especially the new generation of domestic physicists such as Zhou Shaoping and others.
This understanding would last until Gell-Mann proposed the quark model, and the physics community would discover that they were not only a pile of dark clouds above their heads, but also that the ground beneath their feet was also illusory.
Of course.
It has only been a few years since Gell-Mann proposed the quark model, so in later theoretical physics circles, the physicists of this period have a very interesting nickname:
The last honest man.
Immediately afterwards.
Several more members put forward their own opinions:
"Could it be a problem of tension? The surface of the balloon deformed, causing a change in tension?"
"It must have something to do with tension, but what about other values? Don't forget, the balloon will fly around when it is deflated, and there will usually be a rush feeling in the end, which means that the ratio of tension to something must be wrong.
changing."
"Could it have something to do with air resistance?"
"I think it has something to do with gravity..."
The atmosphere at the scene became more and more active as the discussion progressed, and in the end even Zheng Tao and Lin Yu made some analysis.
But we discussed it several times.
In addition to confirming that the situation should be related to tension, the rest of the guesses were quickly denied.
As a result, we were chatting.
Just when everyone was stuck, a sentence suddenly rang out from somewhere on the table:
"Comrade Advisor, why have you been silent all this time? Do you understand the reasons for this situation?"
The word "consultant" has been emphasized a bit.
As soon as these words came out.
The originally lively scene suddenly became silent.
Swish——
Everyone's eyes were once again fixed on Xu Yun, who was sitting in a wheelchair.
The person who spoke could not be said to be hostile or had ulterior motives, but it was obvious that he was not convinced by Xu Yun's title of 'consultant'.
See this situation.
Zheng Tao couldn't help but cast a concerned and questioning look at Xu Yun, the meaning was obvious:
Are you okay?
Xu Yun replied to him with a hint of "Don't worry".
Then he turned to look at everyone and said concisely:
"To be honest with you, I am lucky enough to know the truth of this matter."
"..."
No one said anything at the scene, but some members' faces shrank slightly, looking quite surprised.
To know.
Except for Baozheng.
Although the current members are all under 30 years old, they are basically graduates from prestigious schools, and there are even four international students - this still excludes Xu Yun and Lin Yu.
In the eyes of most people.
If we compare them one by one, they may be different from Xu Yun in terms of ability.
After all, many of them had understood the principle of dampers beforehand, and they thought that there was probably a gap in knowledge between them and Xu Yun - the matter of the weather Doppler radar was asked by Li Jue and others to keep it secret.
But on the other hand.
This gap is not so outrageous that no one can compare to Xu Yun alone. Three cobblers can at least be equal to one Zhuge Liang.
Of course.
A large part of the reason for this mentality is that Xu Yun does not look too old.
If it were an old man in his fifties or sixties, everyone's attitude wouldn't be so complicated.
Seeing Xu Yun express that he knew the truth, Fang Zhong quickly asked:
"Comrade Advisor, could you please explain the rationale for this matter?"
"To tell you the truth, this problem has troubled me for more than three days. I have to think about it for an hour or two every night before I can fall asleep."
Xu Yun glanced at this cool handsome guy, and instead of explaining the principle directly, he asked him:
"Fang...Comrade Fang Zhong, right?"
"Before I explain the principle, I would like to ask you a question first."
Say it.
Xu Yun pointed to the deflated balloon on the table and said:
"Suppose there are nine such small balloons and one large balloon in front of us. Their volumes are the same. Who stores more gas?"
"A small balloon? A big balloon? Or the same number?"
Hear this.
Qiao Caihong, who was behind Xu Yun, blinked and subconsciously said:
"Comrade Han Li, do you even need to ask? Of course there are the same number."
"wrong!"
As soon as Qiao Caihong finished speaking, Lin Yu on the other side shook her head:
"No, this problem is not that simple."
"Although the volumes of nine small balloons and one large balloon are the same, that is, v, it does not mean that their pressures are the same."
"According to pv=nrt, it can be clearly seen that once the pressure is different, the stored gas will also be different."
A question mark immediately appeared on Qiao Caihong’s face:
"ovo?"
Xu Yun smiled at the silly girl, then looked at Lin Yu on the right, and affirmed:
"Comrade Lin Yu is right, this issue is far more complicated than it seems."
"Comrade Lin Yu, can you analyze the difference in pressure between a big balloon and a small balloon?"
Lin Yu thought for a moment, twisted his eyebrows and shook his head slightly:
"Intuition and logic tell me that the pressure of the big balloon must be stronger, but the principle... I don't know."
Xu Yun cast an approving look at the girl.
Which has greater pressure, a big balloon or a small balloon?
This chapter is not finished yet, please click on the next page to continue reading the exciting content! If this question is left in future generations, many people will definitely say it is a big balloon.
The reason is that the shrinkage force of the balloon membrane can be regarded as a spring system, and then it can be directly analyzed qualitatively.
But in fact.
This problem is far from simple.
True.
Simply put, the tension σ should increase with the size of the balloon, that is, the deformation increases.
Don't forget it.
As the balloon expands, 1/r decreases as the size of the balloon increases.
Therefore, if we analyze from the material level, we must establish a non-qualitative model.
This involves the hyperelastic constitutive of rubber, and a generalized hyperelastic model such as the ogden model must be used.
But students who have studied thermodynamics in later generations should all know it.
In addition to the non-directional model of the material, this problem also has a more acceptable physical analysis method.
Think of this.
Xu Yun organized some speech and said to everyone:
"The difference between small balloons and large balloons lies in their size. When the balloon inflates, its surface will begin to become tighter and tighter, and there will always be a tendency to shrink back."
"If the pressure of the gas inside the balloon is the same as the pressure of the gas outside the balloon, then there is no other force that can balance the resilience of the balloon skin."
"So the pressure of the gas inside the balloon is actually greater than that outside the balloon, or it may be that the resilience of the balloon skin compresses the gas inside the balloon."
Speaking of which.
Xu Yun asked Qiao Caihong to push the wheelchair to a blackboard, picked up the chalk and drew a picture.
The shape of the schematic diagram is very simple, and the intuitive description is...
Make a "yeah" gesture, then face horizontally to the left with an arrow on the tip of each of your two fingers.
Then Xu Yun wrote an o where the "fingers" met, and an a in the middle of the arc line connecting the fingertips:
"Please see, the point o here is inside the balloon, and a represents a very small square on the surface of the balloon."
"Because the balloon is inflated, the surface is not flat but has a curved arc."
"As for the surface tension t, it wants to try its best to flatten this arc."
"So, isn't it obvious?"
See this situation.
Many members nodded subconsciously.
really.
There is a curvature on the surface of the balloon, which is a situation statement that elementary school students can understand.
Therefore, although the direction of the surface tension in the diagram is perpendicular to the radius r, it is not perpendicular to the line connecting the center o of the sphere to the center point a of this small area.
If there are no other forces at this time, the film...that is, the surface of the balloon will naturally be unable to maintain balance.
In other words...
There must be a pressure difference on both sides of the balloon skin to offset the force of the surface tension t on the line oa.
Then Xu Yun wrote another derivation:
detf=λ1λ2λ3=1, where λi (i=1,2,3) represents the stretch ratio along three orthogonal directions.
Ψ=∑p=1nμpap(λ1ap λ2ap λ3ap?3).
When p=1,a1=1.
Write Ψ=2μ(λ1 λ2 λ3?3).
Assume that the balloon on the curved surface is subject to equal force in two directions and is free in the x3 direction.
Then the Cauchy stress is written as σ3=?p ∑p=1nμpλ?2ap=0. (Note: I am not sure whether the Cauchy stress has a formula at this time, let’s assume it does, after all, this plot is very important)
Suppose the initial radius of the balloon is r and the initial wall thickness is h. After deformation, the radius is r and the wall thickness is h.
Then the final formula is:
p=2σhr=2λ?3σhr=2hr∑p=1nμp(λap?3?λ?2ap?3).
This time.
There were expressions of understanding on the faces of more people present.
It is not difficult to see from this formula.
The volume element δl/rl is in the middle of the formula, which means that no matter what the values are, such as x, t, yala, etc., δl/r remains unchanged.
In other words...
At this time, divide both sides of the equation by δl with the specific value, and then substitute pv=nrt.
You will find...
p=t/r will first decrease and then increase.
Write here.
Xu Yun put down his pen, spread his hands, and said to everyone:
"Then the answer is obvious."
"As the volume of the balloon increases, the air pressure inside does not increase or decrease blindly."
"Its trend is to decrease first and then increase. This is called extreme point instability."
"When the air pressure decreases, it will be more difficult for us to blow up the balloon."
"When it exceeds the extreme point and becomes a 'big balloon', the internal pressure increases, and it will naturally be much easier to blow up. If the internal pressure is strong, the 'pressure' exerted on the rubber will be greater."
Because of the bandage.
Therefore, no one at the scene noticed that Xu Yun's expression did not have much confidence when he said these words.
no way.
Let alone the neo-hookean model these days, even the varga model has not yet been released.
Without model derivation, the famous 1.4 radius ratio of Xu Yun in later generations cannot be proven.
Therefore, he could only find another way to prove it from the perspective of three parameters of freedom.
Anyway, there is nothing wrong with the numerical values...
And just after Xu Yun finished explaining.
The entire study group was silent for a moment, and then suddenly burst into applause.
Bang bang bang——
Everyone's expressions were not exciting, but most of the doubts in their eyes had dissipated.
Instead, there is goodwill and recognition.
It's just like.....
Xu Yun changed from a sacrifice to a church member?
See this situation.
Xu Yun couldn't help but feel relieved in his heart.
Fortunately, I finally passed the first level smoothly...
Mentioned it earlier.
After meeting Zhou Shaoping, Xu Yun came up with the idea of forming an interest group.
This chapter is not over yet, please click on the next page to continue reading! It’s just that Xu Yun’s original plan was to wait until he had a firm foothold in the base before doing these things.
Unexpectedly, by chance, Zheng Tao and the others wanted to make him their teacher, so Xu Yun had no choice but to take a step back, forcing the interest group to be launched in advance.
But whether active or passive, one thing remains unchanged:
That is, Xu Yun is planning to use the abilities of these youthful elders to do something.
At the same time, he also wanted to see if he could export some knowledge to future generations and try to make the journey of the Chinese physics community in this timeline easier.
After all, it develops normally.
The Chinese physics community will face pressure from Europe and the United States in the next sixty years, and it was not until the advent of solitary point particles that there was some relief.
Regardless of selfishness or justice, there is a prerequisite task that must be solved:
That is to gain the approval of this small group.
Of course.
It’s the same sentence repeated countless times.
The "recognition" Xu Yun needs is not to accept a younger brother, and he is not qualified to have these distinguished people call him big brother.
The approval he needs is more of an equal acceptance, similar to that of friends of the same age.
And judging from the current situation...
This prerequisite task should be considered initially solved.
At least......
These bosses will not openly question their status as ‘advisors’.
Xu Yun then returned to his original position with the help of Qiao Caihong.
Zheng Tao stood up while the iron was hot and asked everyone:
"Comrades, do you have any other opinions about Comrade Han Li serving as a study consultant?"
"...."
Everyone at the scene was silent for a moment and shook their heads.
joke.
Everyone comes to interest groups to learn knowledge. Now there is an obviously awesome boss in the group. Who would be dissatisfied with this kind of thing?
To know.
Many of them were top scorers when they were in school, but after arriving at the base, due to age and ability issues, they have basically not officially joined the theoretical project teams involved in their respective majors.
For example, Zheng Tao and Zhou Shaoping Zhang Gongding them.
These two brothers are usually responsible for all kinds of hard work, such as the casting of Xu Yun's wheelchair, and various tasks for the construction sideline team.
So now there is such an interest group where we can exchange knowledge, and there is a consultant like Xu Yun in the group...
Not an exaggeration.
Some members already wanted to lie down on Xu Yun and suck their brains... ahem, to gain knowledge.
Then everyone briefly chatted about some content.
Some are similar to small phenomena encountered when working with balloons, such as the water hammer phenomenon when water pipes keep sizzling.
Some exchanged their usual reading materials.
For example, "Hunter's Girl", "Red Flag Canal", "Fire King", "The Shadow of Flowers Behind the Curtain", etc...
During this period, Xu Yun occasionally interjected a few words, but more often than not he chose to listen.
After all, this kind of discussion is like lol in the later period.
Carrying alone is actually very boring. At most, someone will send you a few question marks after 1v5 to show your shock, and then it will be boring and empty.
But Happy Five Black is different. That is real happiness, and it is much more interesting than frying fish alone or even going on a blind date.
that's all.
Two hours later.
The first group activity of the ‘Never Update’ interest group concluded successfully.
The group members parted ways. Many of them still had classes to attend in the afternoon.
Qiao Caihong pushed Xu Yun's wheelchair and prepared to return to the hospital to continue today's treatment.
As a result, the two of them didn't go very far.
A familiar greeting came from behind Xu Yun:
"Comrade Han Li, stay!"
Qiao Caihong quickly stopped.
Xu Yun turned his head and looked towards the speaker.
I only see this moment.
Ye Duzheng, who had not been seen for several days, was standing ten meters away from them with a man whose identity Xu Yun could not recognize, smiling and waving to them:
