20 years of teaching

Chapter 215 Characteristics of Sound

Today's situation is different. The leaders of the Education Bureau and the Town Education Committee also came. They had to accompany them, and they couldn't help themselves. As the head teacher, Li Tuanjie came on his own initiative even though he taught Chinese.

This is a rule. If there are guests in the class, as the head teacher, you have to accompany them. This is a kind of respect for the guests and the teacher.

All seven people sat in the back, opened the physics textbook, and read the section "Characteristics of Sound". Lin Feifei told Wang Boda the teaching content of this lesson in advance, and Wang Boda informed everyone who attended the class one by one.

Class has started.

"Stand up!" Wang Jiaxin's crisp and forceful voice.

With a swipe, everyone stood up, including those who came to attend the class. Only Liu Fuliang sat alone. He looked down at the textbook and pretended not to hear the monitor's shout.

"Hello, teacher!" the students shouted and bowed to Teacher Lin.

"Hello students! Please sit down." Lin Feifei bowed slightly in return to the students.

This shocked the people who came to the class today. It is common for students to bow to their teachers, but it is rare for teachers to bow to their students.

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

"I've heard it!" Which child in the countryside has never heard of a cow's call?They often herd cattle.

"Which classmate imitates the sound of a cow?" Lin Feifei smiled.

Many students raised their hands, all male students, while the female students looked back and forth with great 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 the highest.

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

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

The whole class roared with laughter, and Ma Taotao uttered a resounding "moo--", which made the leaders in the back row 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 call differently.

Sometimes the bull disappeared, he imitated the cow's call to attract the bull back.

Sometimes the cow got lost, and he called the cow like a bull to call her back.

Today Ma Taotao imitated the voice of a bull, especially in a low voice.

Ma Taotao is at the age of development, with a thick voice, and the imitation is almost perfect!

Lin Feifan stretched out his hand and pressed it down like a palm, and the classroom immediately fell silent.

Li Tuanjie, who was sitting in the back, felt admiration again. In this situation, he would shout five or six times, "Don't make noise, don't make noise, I tell you not to make noise!"

Only in this way can the students' attention be concentrated, and Lin Feifan only used one movement, which took about 0.5 seconds, and immediately returned the lively scene to a quiet state.

Lin Feifan didn't ask Ma Taotao to sit down, and continued: "I think everyone has heard the sound of mosquitoes. Now, please 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 buzz—" Li Minyao tightly closed her lips, exhausting all her strength...

So sharp!

There was another burst of laughter in the church, someone covered their ears, it was too harsh!

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

"Moo-moo-"

"Buzzing—"

This time, no one laughed, and everyone listened with pricked ears, because the next question was to be answered.

Lin Feifan signaled Ma Taotao and Li Minyao to sit down and asked everyone to discuss the difference between the two voices.

Some people say that the voice of a cow is lower, while that of a mosquito is higher.

Some people say that cows are louder and mosquitoes are quieter.

Wang Jiaxin said loudly that the voice of the cow should be lowered, and the voice of the mosquito should be raised.

The representative of the physics class had already set Wang Jiaxin as the target of pursuit. He was not far behind, and shouted: "The sound of cows is louder, and the sound of mosquitoes is quieter."

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

Students who did not preview the textbooks used popular words to tell the difference between the calls of cows and mosquitoes according to their own feelings.

Students who have previewed the textbooks in advance can use professional physics language to explain the difference between the two from the perspective of physics.

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

Lin Feifei said at the right time that the voices of cows and mosquitoes are different in pitch. In physics, the pitch of a voice is called pitch.

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

Press the steel ruler tightly against the stool surface, and one end sticks out from the tabletop. The extension length is relatively short. Turn the steel ruler and listen to the sound of the ruler vibrating.

Then make the length of the steel ruler protruding from the edge of the table longer, and move the ruler so that the vibration amplitudes of the two times are roughly the same. Pay attention to the difference in the speed of vibration and the characteristics of the sound when the steel ruler makes a sound.

Lin Feifei demonstrated it first, and then asked the students to do it by themselves, and then asked the students to discuss the difference between the two sounds and the difference in the vibration of the two rulers.

After the crackling in the classroom, a lively discussion took place. After some discussion, the students raised their hands one after another.

Some students answered that when the length of the ruler is shorter, the vibration is faster and the sound is sharp and thin; when the length of the ruler is longer, the vibration is slower and the sound is lower.

Li Minyao took the initiative to stand up and made a summary. Objects vibrate fast and the pitch is high, while objects vibrate slowly and the pitch is low.

Lin Feifei said: "Students' exploration activities just now were very successful. Please read the second section of the textbook Chapter 2 "Characteristics of Sound" and answer the following questions."

While the students were reading the textbooks, Lin Feifei 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 vocalization?

5. What is ultrasound?What is infrasound?
6. How much do you know about ultrasound and infrasound in your life?Can you name some of their uses?

After Lin Feifei finished writing the six questions, he walked around among the students. It was expected that the students would announce the time for free discussion after they had read the textbook content once.

There was chatter in the classroom, and there was a heated discussion between front, back, left, and right. Many students probably couldn't discuss the correct answer in place, and left their seats to go to other places to ask students with good grades.

(End of this chapter)