The teacher who teaches undergraduate students at Yan University said to Shen Qi, why are you still coming to class?

There is no word on Princeton's side, and Shen Qi's current identity is slightly embarrassing, he has obtained his undergraduate degree certificate in mathematics, but he can't go to graduate school immediately.

Life seems to be missing a little bit of passion.

To be sure, purely theoretical academic research is a boring affair, and it will be boring for many years until death.

How to seek some stimulation and some fresh vitality in long-term theoretical research, Shen Qi also wants to know the answer.

Shen Qi needs to take the initiative and seek passion in the ordinary.

"Li Zhenqiang!" Suddenly, a professor on the podium yelled and reprimanded him harshly: "What's the matter with you, a student, sleeping for a long time in my big things class?"

Li Zhenqiang woke up suddenly, sleepy-eyed: "I'm sorry Mr. Sun, I was wrong!"

The old professor's face darkened: "My surname is Ren, not Sun! The surname Sun is the one who teaches you the high generation!"

After the end of the substitute class, the first-year students in the mathematics department took a college physics class in the same classroom, and the teacher was called Ren Buqi.

Professor Ren is about to retire, but his temper is very hot: "I can't even remember the teacher's surname, Li Zhenqiang, your usual score is 0 points!"

Li Zhenqiang's name is very domineering, but his personality is not strong, he admits it.

The course of college physics is one of the compulsory courses in the Department of Mathematics, mathematics and physics are you and me, I have you, it is difficult to completely draw a line, and it is the norm to love and kill each other.

Ren Buqi is a professor in the School of Physics, where he teaches college physics classes to non-physics majors.

Professors from the School of Mathematics also teach advanced mathematics classes to non-math majors.

"The final exam is coming next month, and your class of mathematics students is the worst class I have ever taught!" Ren Buqi was furious, the School of Physics of Yan University is strong, and the style of professors in this school is completely different from that of the School of Mathematics.

Shen Qi is very heartbroken, Professor Ren, you are too biased, the average score of our mathematics students this year is definitely beating your physics department, and our physics department is a quarter of the high math. Don't ask me how I know, I'm an informant.

"And you, Shen Qi. Ren Buqi scolded Li Zhenqiang and then reprimanded Shen Qi, "As a squad leader, the attendance rate of your big class is less than 50%, what kind of squad leader, forget it." "The teachers of the Academy of Mathematics don't care much about Shen Qi anymore, but the teachers of the Academy of Physics are very attentive to him.

"I really didn't lead by example. Shen Qi said that he was sorry, he was busy writing mathematics papers and defending his degree this semester, and he really didn't pay much attention to physics.

Now that the bachelor's degree certificate in mathematics is in hand, Shen Qi has made a plan and is ready to make great efforts to attack physics and seek breakthroughs in the branch of mathematical physics.

"There are more than 30 people in your mathematics department, and the number of attendees in this class is 15. There was murder in Professor Ren's eyes, "Shen Qi, what do you say." ”

"I told them to come back to class?" Shen Qi asked tentatively.

"No need. Ren Buqi said coldly.

No need, just three words, only ten strokes.

The meaning of this is understood in the hearts of the students here.

"Okay, don't delay everyone's study time, continue the class. Ren Buqi paced back and forth on the podium, as if thinking.

After standing still, Ren Buqi made up a question: "Remove the desks, chairs, lectern and all other items in this classroom, leaving only me and you, and ask us what is the ratio of the total mass of these people to the air quality in the classroom?" ”

Estimation is a method often used in physics, and in general, it is not required that the results of estimation are accurate, and they should not differ by order of magnitude.

There is often more than one way to estimate, and it is simple and interesting to master, but it is confusing if you can't turn your head.

Professor Ren's current estimation question does not give any specific data, but asks what is the ratio of human mass to air quality in the classroom.

"It's kind of interesting. Shen Qi writes papers every day, and he is irritable when he writes too many papers, and occasionally doing questions is also a way to adjust his physical and mental health.

Shen Qi quickly glanced at the classroom, there were 16 human beings, including one teacher and 15 students. One woman and 15 men.

The height of the classroom is about twice the height of the human body, and the width of the classroom can be estimated to be about 10 times the width of the human body by the number of vertical columns of desks and chairs in the classroom.

Based on the number of horizontal rows of seats in the classroom, including the number of additional rows in the lectern area, it can be estimated that the length of the classroom is about 45 times the thickness of the human body.

Then, the volume of space occupied by a classroom is about 900 times the volume of a person.

Theoretically, this small classroom can be filled with 900 people at the same time, in the same way as stacking blocks, until it is full.

Take 16 to 900 to get an estimate of the ratio of human volume to air volume in the classroom.

The volume ratio is estimated, and a set of density data is needed to get the mass ratio.

So the question is, what is the appropriate value for the density of the human body?

The fact that a person can swim in water indicates that the density of the human body is similar to that of water.

The molar mass of water is 18, and the average molar mass of air can be approximated as 30.

Considering that water molecules are closely arranged, the spacing of air molecules is about dozens of times the size of air molecules.

Shen Qi finally estimated a value, 10.

It can be approximated that the total mass of 16 people in a classroom is 10 times that of the air quality in a classroom.

Shen Qi was a little surprised by this estimate, was it because humans were too light or because the air was too heavy?

The above observations and calculations were all completed in Shen Qi's brain, which took about 15 seconds.

"How much?" Shen Qi asked Ou Ye beside him.

“10。 Ouye also relies on mental arithmetic to arrive at estimates.

That should be right, Shen Qi said to Ou Ye, "You come to answer Professor Ren's question." ”

Ouye raised his hand.

Professor Ren: "Ou Ye, you have estimated it, how much is it so fast?"

Oye: "10. ”

Syllable!

Ren Buqi snapped his fingers: "Ou Ye's thinking is quick, and the attendance rate is close to 100 percent, you should all study like her." That's right, the answer is 10, and the mass of all the people in this classroom adds up to roughly 10 times the quality of the air. We only need to estimate the approximation on the order of magnitude, and we don't have to worry about precision. This is different from your learning advanced generations and numerals, physics is broad and profound, all-encompassing, flexible, and full of fun, do you feel the joy of learning physics?"

Shen Qi found that physics teachers seemed to love snapping their fingers, the teachers of his high school competition team were like this, and the college physics teachers were still like this.

During the recess, Professor Ren approached Shen Qi alone: "I know that you have obtained your bachelor's degree certificate, you can not come to my big things class, but should you urge other students to attend class?"

"It's because I'm not supervising well, and for math students, physics has its significance, and I'll let them go to class to improve the attendance of the whole class. Shen Qi said.

"I heard you won a CPhO gold medal when you were in high school?" Ren Buqi asked.

Shen Qi nodded: "Take it, the teacher of my high school competition team is a graduate of the School of Physics of Yan University and a doctor of astrophysics." ”

"Oh, what's it called?"

"Teacher Mu Rongmu. ”

"It turned out to be Xiao Mu, my student. Ren Buqi said indifferently, and a famous teacher's demeanor arose.

Shen Qi's body shook, I am a student of Teacher Mu, and Teacher Mu is a student of Professor Ren, so according to the word arrangement, Professor Ren is my grandfather!