Take the bus back to school, exactly 8:45 a.m., with 15 minutes to go.

"You can also go to the cafeteria for breakfast first, just at the right time. ”

After breakfast, the two came to the classroom. This is a large lecture hall on the second floor of the No. 2 teaching building, which can accommodate nearly two hundred people. The content of the course is celestial mechanics, and the teacher who teaches this course is an old professor, and the Taishan Beidou in the physics community of the school also has a certain reputation throughout the country. In his early years, he participated in some important scientific research projects of the country, and now he is almost old, and he has already resigned from the university to continue to shine in the field of education.

Li Junhua and Guda sat down very far back in the classroom, and when the class bell rang, the old professor walked into the classroom with the lesson plan. Before the formal class, there is still a routine: roll call.

Li Junhua looked around, Nian Xiaoyue was really not there, so he skillfully took out a Mickey Mouse headband from his schoolbag and put it on his head.

When the teacher was about to read the name, Li Junhua was half-squatting, only showing Mickey Mouse's ears above the table.

"Nian Xiaoyue!"

"To!~" I saw Li Junhua stretching out a hand in the posture he had just made, and the voice he made was slightly perverted.

The old professor helped his reading glasses, saw the raised hand in the back row, nodded, and continued to read.

Although Nian Xiaoyue's academic performance has always been the first in the grade, she has a bad problem - she likes to sleep lazy, and she is almost absent from morning classes. And Li Junhua's characteristic is that he is never absent from all classes, so he naturally became the "spokesperson" of Nian Xiaoyue.

As for why it's so good to study in class, it can probably only be explained by talent. Of course, Li Junhua understands in his heart that today's lazy sleep in Xiaoyue is related to himself.

The old professor finished the roll call and began the class, saying: "Gravitation is universal in the universe, there is a gravitational force between any two objects, and this gravitational force is equal to (the formula of gravitational force). Specific to our earth, whether it is a person or a thing, it will be subject to gravity, why is it subject to gravity?"

"Gravity is the gravitational pull of the earth to us!" a student replied.

The old professor smiled and nodded, and said, "This classmate's answer is very good, but it is not accurate. Gravity is exactly one component of the Earth's gravitational pull to us, because the Earth is always rotating, and the other component is the centripetal force. This centripetal force is different at different latitudes, for example, when the object is on the equator, the centripetal force is maximum, while at the north and south poles, this centripetal force is small. ”

The students listened to it with a bang, because most of them had the same opinion as the classmates just now.

The old professor smiled: "Don't be surprised, students, this centripetal force is very small, only about three thousandths of the gravitational force, so it is not wrong to think that gravity is almost equal to gravity when I do the problem in high school." However," the professor paused, "now that everyone has come to the university, the depth of thinking should also be higher." ”

The professor's words made everyone feel enlightened, and everyone suddenly realized. "So now you might as well think about whether the gravitational acceleration g is a constant or not?"

Li Junhua also fell into a state of thinking, the professor just said that the centripetal force is different in different parts of the earth, and for an object, the gravitational force is certain, so the gravity is definitely different. And gravity is equal to the mass of the object multiplied by the acceleration of gravity g, and the mass of the object is also certain, then - g is not a constant.

After thinking about it, Li Junhua stood up and replied, "Teacher, I don't think g is a constant. It is larger near the poles than near the equator. ”

The old professor nodded with satisfaction after hearing this, "This classmate answered well. The acceleration of gravity g is subject to change. ”

This conclusion made some of the students here jaw-dropping again, because in high school, they had already defaulted to the fact that g was a constant, equal to 9.8 (plus units).

Li Junhua was enjoying the impresses of other students, and the old professor threw out another question: "The masses of different planets in the universe are almost different, and if objects are on the surface of these planets, the gravity is also different." Take the moon that we see every day, and the mass of the moon is now known to be... Now please try to calculate what the gravitational acceleration on the moon is. ”

The students all took pens and calculated on paper, except, of course, those who were sleeping. Li Junhua also calculated for a while, and finally concluded that the gravitational acceleration on the moon is about one-sixth of that on Earth.

I was waiting for the teacher to ask them the answer, and I didn't know which classmate was dreaming or had just woken up, so I asked loudly: "Teacher, do you say that walking on the moon will feel like light work, are there aliens on the moon?"

"Hahaha. ”

The whole class was in an uproar, waiting to see him criticized.

The old professor just smiled when he heard this: "This student is very imaginative, theoretically speaking, people walking on the moon may be light, because the gravitational acceleration of the moon is only one-sixth of that of the earth, but whether it is or not, you have to go for a walk in the future to verify it to know." As for your second question, the teacher can't answer you, so I hope that the students here will be able to answer it in the future. ”

The realm of intellectuals at the level of Taishan Beidou is indeed different, in the face of whimsical and unbelievable ideas, what he did was not to interfere with and strangle or ruthlessly ridicule and sarcasm, but to seek truth from facts to guide him, Li Junhua admired this old professor more and more.

Unconsciously, the bell rang for the end of class, Li Junhua packed up his things and walked out of the classroom with Guda, discussing which cafeteria to go to eat.

Suddenly, he felt someone tap him on the shoulder, Li Junhua looked back, and the three faces were staring at him with good intentions.

Facing such a group of people with expressions like debtors, Li Junhua thought about it and found that he didn't seem to owe anyone money recently, so he said, "Did you recognize the wrong person?" and then prepared to turn around and leave.

Unexpectedly, he was stubbornly clasped by the shoulders of the leader.

"Who are you? Do we know each other?"

Being clasped on the shoulders like this, Li Junhua was a little annoyed.

"Okay, you Li Junhua, I don't even know your grandfather Wang Yang!" the one who grabbed his shoulder spoke.

This Wang Yang is not tall, but his body is quite fat, with a flat head and a big gold chain around his neck, and he looks like an upstart, but he is not worthy of his name at all.

Wang Yang, Li Junhua has also heard of it, he is a junior in the College of Civil Engineering, his family is in the building materials business, quite some assets, this person is lustful, and he likes to use his "Jinyuan offensive" to deceive some ignorant students on weekdays, not only in this school, but also in other schools.

Such a person naturally has a very poor reputation in Southwest Road Mining University, which has "more monks and less porridge", but most people dare not speak out.

"Do you know how to talk to people?" Guda on the side couldn't stand it.

"Is it your turn to speak here?" said a tall and thin man of Wang Yang's two henchmen, a little arrogantly, as he approached Guda.

Li Junhua noticed that there seemed to be something silver in his palm, and when he looked closely, he found that it was a steel pipe, hidden in his sleeve, and his palm held one end of the steel pipe. It seems that the other party came prepared, Li Junhua felt the need to ask clearly, so he said: "I said this benevolent brother, you and I have no grudges in the past and no enmity in the near future, what is the so-called matter today?"