Urban Life: Our Youth

in the afternoon.

No. 15 Middle School, Grade [-] ([-]) Class A.

Geography teacher Sun Zhizheng turned his back to everyone and wrote knowledge points such as perihelion, aphelion, and the angle of the sun on the blackboard.

He is of medium height, slightly fat, and over 50 years old. He has removed the top of his head and wears a pair of glasses. The glasses are placed on the tip of his nose as if they will fall off at any time.

Suddenly, there was a "pop!" sound, and Teacher Sun felt something hit his head. He looked down and saw that it was a piece of chalk about half an inch long.

The students in the classroom roared with laughter.

Teacher Sun stopped writing, turned around, and faced the class of fifty students.

"Who hit me just now?" Teacher Sun asked.

Everyone looked at each other and said nothing.

"What, you have the ability to do this? Don't you have the guts to bear the consequences?" Teacher Sun said.

Everyone still looked at me and I looked at you, silently.

"You guys are covering up for each other, right? Okay, this matter can be easily handled. After class, each of you students will go to the playground and run ten laps, each lap is 400 meters, that is 4000 meters. After running , even if we fail in this matter, what do you think?" Teacher Sun said.

"Teacher, I know who hit you just now." A girl sitting behind Zhang Chuping stood up and said.

"Who is it?" Teacher Sun asked.

"That's him!" Chen Xiaoxiao pointed at Zhang Chuping, "I know he likes to play basketball the most. He is practicing shooting. He once said that if the piece of chalk can hit the core of your head, it will be a successful shot. .”

The classmates in the classroom couldn't help laughing again.

"Very good. Student Chen Xiaoxiao has always been the most honest. Please sit down." Teacher Sun said.

When Zhang Chuping heard this, he gave Chen Xiaoxiao a hard look.

Chen Xiaoxiao made a face at him.

"Teacher Sun, I'm sorry," Zhang Chuping had no choice but to stand up and say, "I...I also made a mistake."

"Zhang Chuping, I know you are famous in school as a slam dunk master. Why did you hit my head?" Teacher Sun said.

"Next... I won't dare next time." Zhang Chuping scratched his hair and said.

"It doesn't matter. I'm not that reserved. Let's just chat openly today, just like good friends. Let's talk about what you have done recently." Teacher Sun said.

"I didn't do anything." Zhang Chuping said.

"Isn't it? I'm afraid I have more information about you than you think. Don't think that I don't know anything. I heard that you often go to the playground to play basketball after school in the afternoon. Play. Basketball is a sport that strengthens the body. I have no objection. However, first, it cannot affect study. However, look at the fact that you have failed the geography exam three times in a row recently. How can this be done? Second, I heard that Your abdominal muscles are well trained, and you have a habit of lifting up your No. 23 basketball vest every time you make a successful shot to show off your abdominal muscles to the girls around you. I wonder if this is the case?" Sun the teacher asked.

"Uh..." Zhang Chuping's face turned red when he heard this, "It turns out that Teacher Sun has always been paying attention to me."

"I guess your trick of 'peacock spreading its wings' will definitely work and attract a lot of opposite sexes, right?" Teacher Sun asked bluntly.

"Teacher Sun, it's not that simple. Girls nowadays are not so easy to deceive." Zhang Chuping said.

When the students in the class heard this, they all laughed.

"Someone also told me that they saw you going to the cinema with a girl. Is this the case?" Teacher Sun asked.

When Chen Xiaoxiao heard this, she looked at him with wide eyes.

"No...no, I heard that the movie "The Wandering Earth" is very popular. I went to see it alone. We met by chance. It was not an agreement in advance. It's hard for me to eat now. Where can I have extra money? Inviting others to watch movies?" Zhang Chuping denied.

Upon hearing this, Chen Xiaoxiao pinched his waist hard from behind, making him grin in pain.

"Really? Well, I believe what you say for the time being," Teacher Sun said, "As the saying goes, laymen watch the excitement, and experts watch the door. You are all sophomores in high school and have learned a lot of geography knowledge. Since you mentioned " "The Wandering Earth", then let's talk about it. "The Wandering Earth" is called a milestone in Chinese science fiction movies. It is very worthy of our high school students' attention. Putting aside the entertainment factor, the most important reason is - science fiction, serious science fiction. It has increasingly become a hot topic for college entrance examination! Whether you have science fiction literacy is increasingly becoming an important criterion for selecting talents for top universities in the future! Did you know? The 2018 National College Entrance Examination Volume 2 is the first time that science fiction works are selected as modern Chinese reading materials; the Ministry of Education in Among the 31 officially recognized national competitions for high school students announced before the Spring Festival, the Science Fiction Literature Competition replaced the New Concept Composition Competition, and the hard core was selected! Therefore, this work is likely to be selected as a college entrance examination question."

"Teacher Sun, it turns out you also know a lot about this movie." Zhang Chuping asked.

"So, I want to ask you, there are many knowledge points in this movie, how many can you name?"

"Helium flash sun. The sun emits heat outwards through the fusion of internal hydrogen nuclei. When the internal hydrogen element is almost consumed, the high temperature and high pressure inside will stimulate the fusion of helium element. At this time, the sun will undergo helium flash. , to put it bluntly, it means that the sun has aged and exploded. This means that the sun has accelerated its aging. After the helium flash, the sun will become a huge but dim red giant. As a result, it will expand after the explosion. By then, it will be so huge that it can even cover the earth. Swallowed. In fact, there is no need for the sun to swallow the earth. The earth has already been vaporized during the helium flash. This is why the earth is equipped with an engine in "The Wandering Earth". Our sun is nearly 50 billion years old. Astronomers It is estimated that the sun still has a lifespan of 50 to 70 billion years. The first helium fusion will occur in 12 billion years, and it is estimated that humans will either die or run away by then," Zhang Chuping said.

"You're right, what else is there?"

"Gravity slingshot, why is the earth captured by Jupiter's gravity? This is the gravitational slingshot effect. Gravity slingshot (also known as gravitational boost) uses the planet's gravity field to accelerate the space exploration ship and throw it to the next target, which is Think of planets as 'gravitational boosters'. This is somewhat similar to centrifugal force. Taking an aircraft as an example, if it flies to the inner planets, it can gain acceleration by facing the sun; while the aircraft flying to the outer planets, even if it has a rocket booster, will not be able to accelerate due to its rocket booster. If the aircraft flies away from the sun, it has to resist the gravity of the sun, so its speed will gradually decrease. Therefore, when the aircraft flies towards the inner planets (such as Venus, but not Mercury, because this planet has no atmosphere), it must use this principle to slow down. And When flying towards an outer planet, it needs to accelerate. When the aircraft approaches the planet from a long distance for the first time, it uses rocket boosters at orbital speed to eventually generate kinetic energy beyond the orbital speed, and the resulting motion effect is like that of the aircraft. It was bounced away by the planet. This series of actions is called planetary gravity-assisted orbit change. In layman's terms, if the orbiting planet is a gang boss, he can only join the gang if he can keep up with my speed. After he comes, he will be my little brother ( Satellite), once you are too fast and overtake me, roll as far as you can... Many aircraft in human history have done this, such as Mariner 10, which passed Venus on February 1974, 2 , arrived at Mercury after decelerating with gravitational assistance, otherwise it would have directly 'run past' due to the gravity of the sun. There was also the Cassini probe, which flew by Venus twice, and then passed by the Earth, Jupiter, and finally We just arrived at Saturn. In "The Wandering Earth", the aircraft was replaced by the Earth. The principle remains the same, but if you want the kinetic energy generated by the Earth Engine Booster to completely exceed the gravity of the sun, you must use the giant body of Jupiter to bounce the Earth away." Zhang Chuping said.

"What you said is very good. Then tell me what Roche limit is." Teacher Sun said.

"The Roche limit, this word sounds very mysterious, but it is actually very simple. The Roche limit means that when the distance between the planet and the satellite reaches a certain level, the tidal effect will cause the celestial body to disintegrate and dissipate. For example: When the distance between the Earth and Jupiter is the Roche limit, the Earth's own gravity is equal to the tidal force caused by Jupiter. If their distance is less than the Roche limit, the Earth will tend to break up and become the rings of Jupiter. Yes, Saturn This is how the ring of Collapse. But if the distance is too far, the gravity is not enough, and it will not be able to reach the third cosmic speed of breaking out of the solar system. It can only turn back and continue to orbit the sun, so taking the risk of approaching Jupiter is the only way for the earth to break out of the solar system. ”

Later, Zhang Chuping explained the knowledge points in the movie such as engine stalling + earthquake, bolide, five steps to escape from the earth, what to do with the moon, etc. He was eloquent and lucid.

"Zhang Chuping, you are good and your lecture is very good, but I don't understand why you always fail the exam?" Teacher Sun asked after patiently listening to him.

"Because the movie is interesting, the knowledge in the geography book is too boring, and my brain gets bigger every time I memorize the book." Zhang Chuping said.

"So, aren't you going roundabout and saying that my geography class is not interesting? Well, you are really good! Other students can be exempted from the 4000 meters and don't have to run. However, you, Zhang Chuping, must finish the whole course for me, and you can't even run one lap. No less!" Teacher Sun said.

"Yes, I promise to complete the task." Zhang Chuping said.