Chapter 663 is not a simple one

"Does anyone know what the circumference of the earth is?" Su Chen asked.

The students of the first class of the third year of high school, you look at me, I look at you, and then they went to turn through the geography books in a uniform manner, and some students who still have physics books are also turning them at the moment.

The geography teacher of the first class of high school is also the geography teacher of the eighth class of high school, and the teachers of the two classes are almost the same, the geography teacher is a girl of a minority ethnic group, who hopes to go out of the village to see the world since she was a child.

As the saying goes, "The world is so big, I want to see it!" ”

But seeing the world requires money, she has liked the mountains and rivers of China since she was a child, she chose to major in geography, and after graduation, she naturally became a geography teacher.

After studying this major, she learned that in addition to the mountains and rivers of the motherland, there are so many beautiful landforms and terrains in the world.

Teaching to make money, vacation travel has always been her life.

The geography teacher was sitting in the back row and looking at Su Chen with a smile at the moment, last New Year's Day she came back from a trip to Japan, but the homework given to her by the students made her look confused.

Later, after asking the students, I learned that this was the homework question given by Su Chen to the students in her name, although the topic itself has many loopholes, but it is very interesting, the students' enthusiasm for doing homework is very high, and she has never collected all the homework in the eighth class of high school, and she saw the homework book of the whole class of the eighth class of high school for the first time.

This almost moved her to tears, it turned out that there were really forty students in the eighth class of high school, when she changed her homework before, she always thought that there were only more than thirty students in the eighth class of high school.

Su Chen's question this time also made her understand a truth, if you want students to like your class, you must integrate knowledge points into what they are interested in, this kind of thing is called humor, and there is no teacher who can do such a thing that is not loved by students.

Maybe these teachers are not the best models, but such a teacher must be a very popular teacher in the eyes of the students, so the geography teacher also came to listen to Su Chen's lecture today.

Unexpectedly, Su Chen's first question today was related to her geography.

The circumference of the Earth's equator is 40,076 kilometers, and she knows that very well.

The person who knows this answer is Cao Xin, who teaches physics, so he naturally knows this.

"The circumference of the Earth's equator is 40,076 kilometers."

A student answered Su Chen's question.

"Okay, then we know the answer from books, but does anyone know how to ask for it?" Su Chen asked.

The students' answers were varied, ranging from satellite rockets to satellites.

"In fact, this question was asked by someone as early as 2,000 years ago." Su Chen said.

Su Chen's words attracted the attention of the students, not only the students, but also some teachers were a little curious.

After all, more than 2,000 years ago, there was no even the circle of the earth, who is this person, who can measure the circumference of the earth.

Wang Wenyun's idea is much simpler, and the scene in her mind at this moment is like this: she is in Lin Siyuan's office, holding a soft ruler to measure the globe on Lin Siyuan's desk.

The man's name was Eratosthenes, a man revered by Western geographers as the father of geography, who lived in Greece in the third century BC and was the administrator of the Alexandria library.

On the day of the summer solstice, he found that the sun could reach the bottom of a well in the city of Sienna, which is now Aswan, Egypt, and now we can easily know that the place must be at 23 degrees 26 minutes north latitude of the earth, which is often called the Tropic of Cancer.

On the day of the summer solstice, the northernmost part of the earth where the sun shines, if this phenomenon is seen by us, what can we generally think of at this time? Damn, it's awesome, the sun is shining directly! Su Chen said.

"Hahaha~" Su Chen laughed at the students in the class.

"What we can think of is too superficial, so we can't be geographers, we can't become mathematicians, and Eratosthenes came up with the idea of using this feature to find the circumference of the earth.

In Alexandria, which is S kilometers away from the city of Sienna, Eratosthenes chose a reference for the seat of the building, and on the day of the summer solstice, the angle 'θ' between the sun's rays and the building was obtained by the length of the shadow, and we all know that sunlight can be seen as parallel light, so that it can be passed by Thales's mathematical law, that is, when a ray passes through two parallel lines, they are equal in opposite angles. ”

"Teacher, what are the two parallel lines?" At this time, Zhou Xiaoxiao asked.

"Did any of your classmates give him an answer?" Su Chen asked.

"The Tropic of Cancer and the equator can be seen as two parallel lines." At this time, Gong Nana said.

"That's right, these are the two, so how do we find the circumference of the earth?" Su Chen asked.

Su Chen did not continue to sell Guanzi, but began to write formulas.

S=θ/360°*C => C=360°S/θ。

"C is the circumference we require, and this angle θ Eratosthenes derives 7 degrees and 12 minutes, one degree is equal to 60 minutes, which translates to 7.2 degrees, that is, one-fiftieth of the circumference angle of 360 degrees.

Then I only need to know the distance S from Sienna to Alexandria, and we can find the circumference of the earth.

This S distance, Eratosthenes naturally found it, and finally, obtained C = 39360km, although the answer is a little different from the present, after all, it was more than 2,000 years ago, and the measurement equipment is inaccurate and inevitably errors.

But this result is very different from the current measurement results, it is completely acceptable, through the circumference of the earth, we can also get the radius of the earth, isn't it amazing, the earth, this sphere that we can't imagine, we can actually calculate its circumference on paper. ”

The students at the bottom are still unsatisfied, after all, this kind of lecture seems to irrigate the knowledge points on the way to tell the story.

Su Chen asked the students to do the math by themselves, and slowly absorbed it before continuing, "What kind of truth can we draw through this question?" ”

Su Chen's question is very extensive, students, you look at me, I see that you didn't speak.

The teachers below are also very curious, after all, Su Chen's lecture method is more interesting, and the students are easy to accept, even Wang Wenyun, who usually hears mathematics as if listening to heavenly books, listens to it with relish at the moment.

Seeing that the students didn't answer, Su Chen said to himself, "This question tells us a truth, that is, from ancient times to the present, none of the people who have been librarians are simple!" ”

"Hahahaha~"

Su Chen's words caused the whole class to burst into laughter, because their homeroom teacher Wang Wenyun is the school's librarian, and many celebrities have also served as librarians.

Didn't you see that Brother Yun's face was red with laughter, when Su Chen talked about the librarian, the other teachers and students were looking back at Wang Wenyun, which made Brother Yun a little shy.

It's just that there is a person whose face is not so good at this moment, that is Lin Siyuan, seeing his eldest daughter and Su Chen interacting so happily, he is a little unhappy in his heart.