20 years of teaching

Chapter 98 Physics Lessons

After taking a nap at noon, Lin Feifei got up early, because he had a class in the first period of the afternoon, which was physics class, so he was always a little uneasy.

Taking an unfamiliar physical education class is very relaxed and casual.

You must be very serious when taking the courses of this major.

Although he had taken a physics class for one and a half months during the internship, Lin Feifan still made sufficient preparations this time, and prepared many class hours in advance.

I always feel that if I don't prepare carefully, there will be problems in class.

What makes him regret is that many experiments that can improve students' interest in learning physics cannot be done because there is no experimental equipment.

I remember that during the internship, before each class, I could find the corresponding experimental equipment in the laboratory, and I could do demonstration experiments in each class. The classroom atmosphere was very active, and the students' enthusiasm for learning was so high.

But that was a school in the city, and now it is in the country.

Recalling his internship time, Lin Feifei envied the teaching conditions of urban schools.

The first physics class was still in the second ([-]) class of junior high school, and the students were still immersed in the memories of the physical education class in the morning. When Lin Feifan walked into the classroom, there was a burst of cheers in the classroom.

Many people mistakenly think that it is another physical education class.

The provisional timetable hasn't been printed yet, so it looks like the kids don't know this class is physics yet.

"Take out the physics textbook?" Lin Feifan raised the textbook in his hand and said.

It turned out to be a physics class.

The students were not disappointed, they were still very happy, after all, it was their first physics class.

When the books were first distributed, everyone picked out the physics textbooks and took a closer look. Some of the questions and knowledge in it, as well as various illustrations, looked very interesting.

The first time I saw something, the first time I did it, I felt very fresh and naturally excited.

Lin Feifan was not in a hurry to ask the students to open the textbooks at first, but first let the students familiarize themselves with the front and back covers of the textbooks, and said with a smile that among all the textbooks, even the physics textbook is the most beautiful.

If you don't believe me, compare now.

Everyone took out Chinese, mathematics, English, history, politics, etc. textbooks and looked at them carefully.

Hey, it's really the most beautiful physics textbook.

Most of the students nodded their approval, and some shouted that the physics teacher was also the prettiest of them all.

As a result, more people nodded frequently in the classroom.

Especially girls, their faces were flushed with excitement, and their eyes were shining with hot brilliance.

Lin Feifan continued: "Not only are the textbooks beautiful, physics is also the most interesting subject."

The classroom quickly fell silent, waiting for the next sentence.

Empty talk without evidence, how can it be interesting?Physical education is fun.

Lin Feifan said: "Physics is a subject based on experiments. Many experiments are very interesting to do."

At this time, Lin Feifei felt that if he had the experimental equipment and did some demonstration experiments, the students would definitely show a strong interest.

But now it's bare-handed, so I have to do a few experiments with bare hands, or blow it with my mouth.

Lin Feifan stretched his hands to his mouth and said, "Students do it together with me, put your hands close to your mouth, breathe out on your hands, please answer, how does it feel?"

Everyone put their hands to their mouths and breathed hard.

Shouts erupted in the classroom.

"It's warm."

"It's hot."

"Hot."

"It smells."

"It smells bad."

"Didn't you brush your teeth this morning?"

……

Isn't this a common way to warm your hands in winter?How can it be fun?
After demonstrating how to exhale, Lin Feifei continued, "Blow into your hands again to experience how it feels."

puff--

puff-

Hey, this time it feels cool!

"Why are the feelings completely different twice?" Lin Feifan asked in due course.

The classroom suddenly fell silent, and everyone was thinking about it. It's not unusual to do these two movements individually, and it would be interesting to do them together.

One ha and one blow, one warm and one cool, the feeling is completely opposite, what is the reason?

The students began to chatter, giving many different reasons.

Lin Feifei listened carefully, and found that none of the answers were completely correct, and they were all one-sided.

There is also the answer that the bull's head is wrong with the horse's mouth, which is almost nonsense.

This is totally normal, just the first day of physics class.

Of course, it is not ruled out that some students are making a fuss, deliberately talking nonsense, trying to make people laugh and show off.

"Everyone watch me do another experiment." Lin Feifei turned around and approached the blackboard, breathed on the blackboard, then stepped aside, drew with his finger on the place where he breathed, and saw that the place where he breathed was wet, "Did you see this? The place is wet, what's going on?"

"It's wet." Some students said.

"The teacher moistened it with his tongue." A naughty student shouted from the back of the classroom.

Suddenly, there was a burst of laughter.

Lin Feifan didn't lose his temper. He smiled and asked a classmate in the front row to stand up, and asked, "Prove it, did I stick out my tongue just now? Did I add it?"

The little girl who stood up shook her head like a rattle and blushed.

After asking the girls to sit down, Lin Feifei signaled the student who shouted and licked the wet to go to the blackboard, and asked him to cooperate with the teacher to finish wetting the blackboard.

The man behind scratched his scalp with one hand and touched his buttocks with the other, and walked up to the podium shyly.

I regret it now, I really shouldn't have yelled just now.

If you don't have water on hand, you can't spit on the blackboard.

The chubby boy had no choice but to breathe hard at the blackboard, only to see that a large piece of the blackboard was wet.

Lin Feifan hurriedly pulled the fat boy aside, pointed to the blackboard and said, "Look, everyone, is the blackboard wet by him or wet?"

"Ha wet!" The sound was deafening.

No one dared to say that it was licked wet.

Lin Feifan patted the fat boy on the shoulder, told him to go back to his seat, and praised him for successfully doing a physics experiment, which was great.

Then Lin Feifan asked the students to turn to Chapter 3 "Changes in the State of Matter" in the textbook, and combined with the textbook, he explained that the principle of wetting the blackboard is exactly the same as the principle of warming the hands just now.

The hot water vapor exhaled from the mouth will liquefy into water when it encounters a cold object surface, and release heat, so it plays the role of warming hands.

Steamed steamed buns, steamed buns, steamed meat, and steamed fish take advantage of this principle, that is, heat should be released during the liquefaction process.

So what is liquefaction?

Liquefaction is the process of changing a substance from a gaseous state to a liquid state.

When high-temperature water vapor encounters a cold object, a large amount of heat will be released.

Therefore, beware of being scalded by high-temperature water vapor, which is much more serious than being scalded by boiling water, because there is an additional liquefaction and exothermic process.

Lin Feifan pointed to the blackboard again and asked, "The blackboard is dry again now, where did the water go?"

"To the air."

"It's dry."

"Scattered."

……

Li Minyao stood up and looked at the textbook and said, "When it evaporates, the liquid water becomes water vapor, and water vapor is invisible."

Lin Feifan stretched out his thumb and praised: "Please sit down, the answer is very good! You used physical language to answer the question. From today onwards, when we answer physics questions, we must use concise physical language to answer, and we cannot use Answer with the spoken language in daily life.”

So what is physical language?Physics language is a professional physics term, which is physics knowledge, which comes from physics textbooks.

By listening to lectures, reading books, reciting, and understanding carefully, you can master physical language well.

Lin Feifan then explained that the opposite process of liquefaction is vaporization, and liquefaction releases heat, so heat must be absorbed during the vaporization process.

There are two methods of vaporization, evaporation and boiling.

The speed of evaporation is related to three factors, the temperature of the liquid, the surface area of ​​the liquid, and the velocity of the air near the liquid.

Blowing air to the hands speeds up the flow of air on the skin surface and accelerates evaporation, which absorbs heat and has a cooling effect, so people feel cool.

(End of this chapter)