Today's situation is different. The leaders of the Education Bureau and the town education committee are here. They have to accompany them and cannot help themselves. As the head teacher, Li Tuanjie, although he teaches Chinese, he also came on his own initiative.

This is a rule. If a guest comes to the class to listen to the class, the class teacher must accompany the class. This is a sign of respect for the guest and the teacher.

The seven people sat in the back, opened the physics textbook, and browsed the section "Characteristics of Sound". Lin Feifan told Wang Boda the teaching content of this class in advance, and Wang Boda informed everyone in the class one by one.

Class has started.

"Stand up!" Wang Jiaxin said in a clear and powerful voice.

Everyone stood up, including those who came to attend the lecture. Only Liu Fuliang sat alone. He lowered his head and looked at the textbook, pretending not to hear the monitor's shout.

"Hello, teacher!" The students bowed to Teacher Lin in unison.

"Hello, classmates! Please sit down." Lin Feifan smiled and nodded.

After the pre-class etiquette was completed, Lin Feifan asked the first question: "Have you ever heard the sound of a cow braying?"

"I've heard it!" Which child in the countryside has never heard the braying of cows? They all often herd cows.

"Which classmate can imitate the sound of a cow's braying?" Lin Feifan said with a smile on his face.

Many students raised their hands, all of them were male students, while the female students looked back and forth with interest to see which students could imitate the sound of a cow.

Ma Taotao is the tallest in the class, and his hands are also raised highest.

Lin Feifan named Ma Taotao to imitate the sound of a cow.

Ma Taotao stood up, scratched his scalp with his hands, blinked his eyes, pondered for a moment, and pulled his chin down: "Moo-moo-"

The whole class burst into laughter, and Ma Taotao said a loud "moo——" again, making everyone in the class laugh.

Ma Taotao has two cows at home, one male and one female. He often grazes the cows at home and knows that bulls and cows have different sounds.

Sometimes the bull disappears and he calls like a cow to attract the bull back.

Sometimes the cow gets lost, and he calls the cow back by imitating the bull's cry.

Today Ma Taotao imitated the sound of a bull, which was especially deep.

Ma Taotao is in his prime and has a rich voice, and his imitation is so perfect!

Lin Feifan stretched out his hand and pressed it down in the shape of a palm, and there was immediately no sound in the classroom.

Sitting in the back, Li Tuan Tuan felt admiration in his heart. In situations like this, he would shout five or six times, "Don't make a noise, don't make a noise, I told you not to make a noise!"

In order to focus the attention of the students, Lin Feifan only used one action, which took about 0.5 seconds, and immediately brought the lively scene back to a quiet state.

Lin Feifan did not ask Ma Taotao to sit down, but continued: "Everyone must have heard the sound of mosquitoes. Now ask a classmate to imitate the sound of mosquitoes."

This time, more students raised their hands. Not to be outdone, girls raised their hands more than boys.

This time Lin Feifan named Li Minyao to complete this task.

"Buzz buzz--" Li Minyao closed her lips tightly and used up all her strength...

So sharp!

There was another burst of laughter in the church, and some people covered their ears. It was too harsh!

Lin Feifan signaled everyone to calm down and said, "Now let's do it again. Ma Taotao imitates the sound of a cow braying, and Li Minyao imitates the sound of a mosquito. Listen carefully. I want you to tell the difference between the two sounds."

"Moo-moo-"

"Buzz buzz-"

This time no one laughed, and everyone listened carefully because they had to answer questions next.

Lin Feifan motioned to Ma Taotao and Li Minyao to sit down and asked them to discuss the difference between the two sounds.

Some people say that cows have a lower voice, while mosquitoes have a higher voice.

Some people say that the noise of cows is louder, while the noise of mosquitoes is softer.

Wang Jiaxin loudly said that the sound of cows should be lowered and the sound of mosquitoes should be raised.

The physics class representative had already targeted Wang Jiaxin. Not to be outdone, he shouted: "The voice of a cow is loud, but the voice of a mosquito is small."

Fang Yongzhi, who was sitting in the back, nodded slightly, approving of this teacher-student interaction. This time, the students first understood the difference between pitch and loudness from the senses.

Students who had not previewed the textbook used popular language to talk about the difference between the sounds of cows and mosquitoes based on their own feelings.

Students who have previewed the textbook in advance can use professional physics language to explain the differences between the two from a physical perspective.

It seemed like a simple and interesting ventriloquism performance, asking male students to imitate the sounds of cows and asking female students to imitate the sounds of mosquitoes. Fang Yongzhi could see that it was all carefully planned.

Lin Feifan pointed out at the right time that the sounds of cows and mosquitoes have different pitches. In physics, the pitch of sounds is called pitch.

So what factors determine the pitch? Lin Feifan lifted a stool and placed it on the podium, picked up a steel ruler and pressed it on the stool, and asked the students to use their own rulers to imitate him and do a demonstration experiment.

Press the steel ruler tightly on the bench surface, and extend one end of the table to a relatively short length. Move the steel ruler and listen to the sound of the ruler vibrating.

Then make the length of the steel ruler extend beyond the edge of the table longer, and move the ruler so that the amplitude of the two vibrations is roughly the same. Pay attention to the speed of vibration and the difference in sound characteristics when the steel ruler makes sounds.

Lin Feifan first demonstrated it once, then asked the students to do it themselves, and then asked the students to discuss the difference between the two sounds and the two vibrations of the ruler.

After the classroom was crackling, a lively discussion started. After the discussion, everyone raised their hands.

Some students answered that when the ruler extends shorter, it vibrates faster and the sound is sharper and thinner; when the ruler extends longer, it vibrates slower and the sound is deeper.

Li Minyao took the initiative to stand up and made a summary. When an object vibrates fast, the pitch is high, and when an object vibrates slowly, the pitch is low.

Lin Feifan said: "The research activity just now was very successful. Please read Chapter 2, Section 2 of the textbook "Characteristics of Sound" and answer the following questions."

While the students were reading the textbook, Lin Feifan wrote six questions on the blackboard:

1. What is the physical meaning of frequency? What is frequency?

2. In the International System of Units, what is the unit of frequency?

3. Try to explain the relationship between the speed, frequency and pitch of an object's vibration.

4. What is the frequency range that most people can hear? What is the frequency range of human vocalizations?

5. What is ultrasound? What is infrasound?

6. How much do you know about ultrasound and infrasound waves in life? Can you tell me some of their uses?

After Lin Feifan finished writing the six questions, he walked around among the students. It was expected that after the students had read the textbook content, he announced that it was time for free discussion.
Chapter completed!