Sound phenomenon is a necessary test point in physics, which is relatively simple and the key to getting points. The knowledge points of physical sound phenomena summarized below are what I want to share with you. Welcome to browse.

1, sound is produced by object vibration.

Conditions for vocalization: first, there must be a vocal body; Second, the vocal body should vibrate.

2. The sound source of the vibrating object.

3. Everything that makes a sound is vibrating, the vibration stops, and the sound stops, but the sound doesn't necessarily stop.

4. Gases, liquids and solids can all make sounds due to vibration.

For example, wind, rain, reading sound and reading sound are the sounds made by the vibration of gas, liquid and solid respectively.

5. Sound transmission needs media. Solids, liquids and gases are all media, and vacuum cannot spread sound.

For example, astronauts on the moon can only talk by radio waves. Sound travels in the form of sound waves

6. Sound speed: the distance that sound travels every second. The speed of sound propagation is related to the type and temperature of the medium.

Sound travels fastest in solid, second in liquid and slowest in gas. At 15℃, the speed of sound propagation in air is 3x108m/s.

7. Echo: The sound is reflected when it meets an obstacle, and then it is introduced into the human ear to form an echo.

Only when the echo reaches the human ear more than 0, 1 sec later than the original sound, or when the obstacle is at least17m away from people, can the human ear distinguish it from the original sound, otherwise it will be mixed with the original sound, and the echo will strengthen the original sound.

8. Note: Don't think that as long as an object vibrates, it will definitely make a sound that can be heard by the human ear.

9. Don't think that as long as you hear the sound twice, it must be an echo. If you don't hear it twice, there must be no echo.

10, the process of people hearing sound: the external sound causes the tympanic membrane to vibrate, and this vibration is transmitted to the auditory nerve through the ossicles and other tissues, and the auditory nerve transmits the signal to the brain, and people hear the sound.

1 1. Two ways of sound transmission: ① air conduction; ② Bone conduction.

12. There are two ways for human ears to hear sounds: ① sound waves-auricle-external auditory canal-tympanic membrane-ossicular bone-auditory nerve-brain; ② Sound wave-ossicular bone-auditory nerve-brain.

13, the human ear must have the conditions to hear sound:

First, the sounder vibrates 20-20000 times per second; Secondly, there must be a medium to spread sound; Third, there must be a good organ (human ear) to receive sound.

14, binaural effect:

The distance from the sound source to the two ears is generally different, and the characteristics such as the time when the sound reaches the two ears are also different, so that the position of the sound source can be judged.

Application: Because of binaural effect, all the sounds we hear are stereo.

Note: don't think that people can't perceive sound without hearing.

15, concept: the sound level is called tone.

16, the key factor: the vibration frequency of the sound generator. The higher the frequency, the higher the pitch.

17, frequency: 1 second, the number of times the sounding body vibrates, unit: Hz, symbol: Hz.

The hearing range of human ear: 20-20000 Hz. The sound below 20Hz is called infrasound, and the sound above 20000Hz is called ultrasonic. (The frequency of contraction waveform is high)

18, concept: the strength (size) of sound is called loudness.

19, loudness factor: the amplitude of the sounding body. The greater the amplitude, the greater the loudness. Loudness is also related to the distance between the human ear and the vocal body. The farther away from the vocal body, the less loudness.

20. Ways to increase loudness: First, reduce the dispersion of sound; The second is to reduce the distance from the human ear to the sound source.

2 1, timbre concept: the quality of sound.

22. Factors that determine the timbre: Precautions for the vocal body itself: Don't think that the sound is high, and the loudness must be large.

23. The concept of noise: ① the sound made by the vocal body when it vibrates irregularly.

(2) All sounds that affect people's normal study, work and rest, as well as those that interfere with people's listening, belong to noise.

24, noise level and harm

(1), people use decibels (dB) as the unit to express the strength of sound.

(2) The lower limit of hearing is 0dB. In order to protect hearing, the sound should not exceed 90dB. In order to ensure that the sound of work and study should not exceed 70dB.

In order to ensure that the sound of rest and sleep does not exceed 50dB.

25, noise control:

(1) to control noise generation; (2), blocking the spread of noise; (3) Weakening in human ears.

Note: don't think that beautiful music must not be noise; Don't think that 0dB of sound means no sound and no object vibration.

26, using sound to transmit information: such as B-ultrasound, sonar.

27, using sound to transmit energy: such as: ultrasonic cleaning precision instruments; Crushing the substance with ultrasonic waves; Ultrasonic dust removal and tooth cleaning.

Short answer

1. Is the continuous thunder heard during thunder formed by continuous thunder? Why?

A: No, the continuous thunder heard during thunder is the result of the sound being reflected by mountains and clouds many times, forming an echo.

2. In the summer of 2002, five students in Peking University climbed Mount Everest and an avalanche occurred, which caused a serious accident. Please analyze: why don't you shout loudly when climbing in the snow?

A: When climbers or explorers enter snow-capped mountains or caves, it is generally forbidden to make loud noises. This is because the support of snow drifts on mountains and rocks in caves may be very fragile. Shouting loudly will cause air vibration, and when it reaches snow drifts or rocks, it will cause them to vibrate, which may cause avalanches or cave collapses, thus endangering people's lives and property. Therefore, don't make any noise when entering such areas.

Please imagine what will happen in our world if the speed of sound is 0. 1m/s? Please write four relevant and reasonable scenarios.

Answer: (1) When two people talk face to face, it takes some time to hear clearly. (2) Thunder cannot be heard for a long time after lightning;

(3) It takes a long time for athletes to start after the starting gun goes off; (4) When setting off fireworks, it will take a long time to hear the salute after seeing the fireworks.

Let a classmate sit in the middle of the classroom blindfolded. Then, you stand in front of or behind your classmates and give them high five. Can this classmate accurately judge where to high-five? Why?

Answer: You can't correctly judge the position of the high-five, because people judge the direction of the sound source through the "binaural effect", and when you stand in front of or behind your classmates and high-five, the distance from the sound source to both ears is the same, so there is no difference in the time felt by both ears, and there will be no binaural effect, so you can't accurately judge the direction of the sound.

After Beethoven was deaf, he just bit one end of the stick with his teeth, and the other end leaned against the piano to listen to the sound of his playing, so as to continue his creation. Please explain the reason.

Answer: Sound can also reach the auditory nerve through the skull and jaw, causing hearing. Beethoven wrote in this way, that is, bone conduction.

6. If you are a stage sound engineer, how can you make the audience hear better stereo?

Answer: Put more microphones around the sound source, and correspondingly put more speakers (sound boxes) around the audience, so that the audience can hear better stereo sound.

7. Bite your watch with your teeth and cover your ears with your hands. You will hear the ticking sound strengthened many times. What does this mean?

A: Bones can transmit sound, and the sound transmission effect is very good.

8. Many deaf people with complete internal hearing can dance to the beat of music. Do you know why?

Answer: This is because the sound of music reaches the eardrum through the floor and his bones, making it vibrate to produce hearing.

9. Pour boiling water into an empty thermos. How does the sound from thermos come about? What is the changing law of this sound?

Answer: When the thermos bottle is filled with water, the air column on the water surface vibrates and makes a sound. As the water surface rises, the air column above becomes shorter and the vibration of the air column accelerates, making the tone emitted by the air column higher and higher. The vibration amplitude and loudness of the air column become smaller.

10. In winter, the cold wind blows on the wires in the wild, making a purring sound, which can't be heard in summer. Why?

Answer: Due to the cold weather in winter, the wires contract due to cold, and the vibration frequency is high and the tone is high; In summer, the weather is hot, the wires expand and relax, the vibration frequency is low and the tone is low.

1 1. When a bee flies with nectar, its wings vibrate 300 times per second on average, and when it does not carry nectar, it vibrates 440 times per second on average. Experienced beekeepers can tell whether bees have collected nectar. What is the basis of this distinction?

A: Depending on the tone of the voice. When bees carry nectar, the frequency of wing vibration is small (300 times/second) and the tone is low; Without nectar, the vibration frequency of wings is high (440 times per second), with high frequency and high tone.

12, people can't hear the sound of butterflies flying, but they can hear the hum of mosquitoes flying around. Why?

Answer: The frequency range of sound that can cause human hearing is 20~20000Hz, and the frequency of butterfly wing vibration is less than 10Hz, which is lower than the hearing range of human ears, so human ears can't hear the sound of butterflies flying; The vibration frequency of mosquito wings is 500~600Hz, and within the hearing range of human ears, human ears can hear the sound made by mosquitoes when flying.

13. Some people say that music is musical sound, so musical sound will not become noise. Do you think this view is correct?

A: This view is wrong, because from the perspective of environmental protection, all sounds that hinder people's normal rest, study and work are noise, and sounds that interfere with what they want to hear are also noise, so music sounds can be turned into noise.

14, the sound transmission performance of the wall is much better than that of the air, but the sound entering the room from the outside is obviously weakened after the doors and windows are closed. Why?

A: When sound propagates in the air, it will be mostly reflected when it meets obstacles such as walls and glass. Therefore, after the doors and windows are closed, the sound transmitted to Yin will be weakened, which is a way to reduce the noise during transmission.

15. Why do civilized and hygienic cities require planting trees and grass?

A: Planting trees and grass can not only beautify the city, but more importantly, trees and flowers can absorb and reduce noise, make the city quieter, let people relax and enjoy nature.

16. If you are a planner of urban construction, what measures will you take to reduce the harm caused by noise?

Answer: ① Plant trees and grass; ② Set up sound insulation boards; ③ Factory, workshop, entertainment place, etc. Away from residential areas ④ It is forbidden to whistle in urban areas.

17. The noisy roads in winter are particularly quiet after snowfall. What is the reason?

A: The noise on the road mainly comes from the noise made by various motor vehicles. After the snowfall, the road was covered with a thick layer of snow. At this time, the snow on the road is softer and becomes a better sound-absorbing material, and the noise is absorbed by the snow. Therefore, the road after snowfall is much quieter than usual.

18, there is such a scene in the science fiction film: a spaceship is in distress in space, and on the way to rescue another spaceship, it suddenly hears the huge explosion of the distressed spaceship, and then sees the explosion fire. Please point out two scientific mistakes in this scene to the director.

Answer: (1) Hear the explosion in space (no explosion in vacuum) (2) Hear the explosion first and then see the explosion fire (the speed of light is faster than the speed of sound).

29. What is the difference between the propagation of light and sound?

Answer: (1) Light can propagate in a vacuum without medium; The transmission of sound needs medium, and vacuum cannot transmit sound.

(2) Generally speaking, the greater the density of the medium, the smaller the speed of light, but the greater the speed of sound.

(3) The speed of light is much faster than the speed of sound.

20. Why do you speak louder in the house than in the wild?

Answer: When talking in a room, the echo and the original sound are mixed together to strengthen the original sound, so it sounds louder.

2 1. The wall of the cinema projection hall is decorated with potholes, commonly known as "swallowing mud". What is its purpose?

A: Mud swallowing is bumpy. Its function is to prevent the sound hitting the wall from being reflected to the audience, thus avoiding reverberation, that is, weakening the echo.

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