Ask for advice on physics 8th grade book unit 1 acoustic phenomena information

"Acoustic phenomena" review outline

I, the occurrence and propagation of sound

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1. textbook P12 page Figure 1.1-1 of the phenomenon illustrates that: all the sound-producing objects are vibrating. Pressing a tuning fork with your hand to pronounce a sound, the sound also stops, the phenomenon shows that the vibration stops and the sound also stops. The vibration of the object called sound source.

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Exercises: ① human speech, singing by the vibration of the vocal cords, the melodious bird song by the vibration of the membrane of the sound, the crisp cricket chirping by the vibration of the wing friction of the sound, the frequency of its vibration must be between 20-20,000 times / second.

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② "Yellow River Cantata" in the lyrics of "the wind is roaring, the horse is barking, the Yellow River is roaring", where the "roar", "barking" The sound sources of "roar" here are the air, the horse and the Yellow River water respectively.

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③Tap on the table, hear the sound, but can not see the table's vibration, what can you think of to prove the table's vibration? You can sprinkle some scraps of paper on the table, which will jump when the table is tapped.

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2. The propagation of sound requires a medium, a vacuum can not transmit sound. In the air, sound travels in invisible sound waves, which reach the human ear and cause the tympanic membrane to vibrate, and the person hears the sound.

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Exercise: ① P14 Figure 1.1-4 shown in the experiment can be concluded that the vacuum can not transmit sound, there is no air on the moon, so even if the astronauts on the moon are very close to each other, but also rely on the radio phone conversation, because radio waves can also be propagated in a vacuum, the speed of propagation of radio waves is 3 × 108m / s.

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② "The sound of wind, rain, reading, sound into the ear" shows that: gases, liquids, solids can be sound, air can spread the sound.

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3. The speed of sound propagation in the medium is referred to as the speed of sound. In general, v solid>v liquid>v gas, the propagation speed of sound in air at 15 ℃ is 340m/s or 1224km/h, and the propagation speed in a vacuum is 0m/s.

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Exercise: ☆ There is a section of steel pipe containing water, the length of which is L. Knock at one end, and you will hear the sound 3 times at the other end. The transmission times are in order from shortest to longest.

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☆When a 100-meter race is run at a sports meeting, the finish line referee should mark the time when he sees the gun emitting smoke. If the gun is heard and then the time is recorded, the recorded time is 0.29s later (earlier, later) than the actual running time (when the air is 15℃).

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☆The following experiments and examples can illustrate the conditions for the production or propagation of sound (① ② ④) ① put some crushed foam on the surface of the drum, and when the drum is struck, you can observe that the crushed foam keeps beating. ② put in a vacuum cover of the cell phone, when there is an incoming call, only see the indicator light flashes, can not hear the ringtone; ③ take a piece of cardboard, let it in the teeth of the wooden comb crossed, once faster and once slower, compare the two different; ④ gong sound, press the gong with your hand, the gong sound will stop.

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4. Echo is formed when sound is reflected back from obstacles encountered in the process of propagation. If the echo arrives at the human ear than the original sound later than 0.1s the human ear can distinguish the echo from the original sound, this time the obstacle to the listener's distance of at least 17 m. Talking in the house than in the wilderness sounds loud, the reason is that the house space is relatively small caused by the echo arrives at the human ear than the original sound later than the final echo of less than 0.1s and the final echo and the original sound is mixed together to make the original sound strengthened.

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Exercise: the use of echo can determine the depth of the sea floor, icebergs distance, the enemy submarine's proximity to the measurement of the first to know the speed of sound propagation in seawater, the measurement method is: measure the sound to be reflected back to the sound signal time t, find out the propagation speed of the sound in the medium v, then the point of the sound from the object S = vt/2.

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2, we how to use the sound of the sea floor to determine the depth of the sea floor, icebergs distance, the enemy submarine's proximity.

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1. Sound in the ear propagation pathway: the sound from the outside world caused by the tympanic membrane vibration, this vibration through the auditory bone and other tissues to the auditory nerve, the auditory nerve signal to the brain, the person hears the sound.

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2. Deafness: divided into neurological deafness and conductive deafness.

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3. Bone conduction: sound conduction can not only use the ear, but also through the skull, jawbone to the auditory nerve, causing hearing. This type of sound conduction is called bone conduction. Some people who have lost their hearing can hear sounds in this way.

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4. Binaural effect: People have two ears instead of one. The distance from the sound source to the two ears is generally different, and the moment, intensity and other characteristics of the sound transmitted to the two ears are different. These differences are an important basis for determining the direction of the sound source. This is the binaural effect.

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Three, music and three characteristics

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1. Music is the sound made by an object doing regular vibration.

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2. Pitch: the height of a sound as perceived by a person. With a piece of cardboard in the teeth of the comb fast and slow rowing can be found: rowing fast pitch, with the same large force toggle the thickness of different rubber bands can be found: rubber band vibration fast sound pitch. Comprehensive two experimental phenomena you get *** with the conclusion that: the pitch and the frequency of vibration of the sound body has a relationship, the higher the frequency of the higher pitch; the lower the frequency of the lower pitch. The number of times an object vibrates in 1s is called frequency, the faster the object vibrates, the higher the frequency. Frequency unit times / second is also recorded as Hz.

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Exercise: explain the flight of bees can be detected by hearing, why the flight of butterflies can not be heard? Bee wing vibration sound frequency in the human ear hearing range, butterfly vibration frequency is not in the hearing range.

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3. Loudness: the size of the sound perceived by the human ear. Loudness is related to the amplitude of the generator and the distance from the sounding distance. Objects in the vibration, the maximum distance from the original position is called the amplitude. The greater the amplitude, the greater the loudness. The main way to increase the loudness is to reduce the dispersion of the sound.

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Exercise: ☆ A baritone singer sings, and a soprano sings softly with him: the soprano sings low in pitch, and the baritone sings high in pitch.

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☆The confetti scattered on the drum surface will jump when you beat the drum, and the louder the drum, the higher the jump; the tuning fork will touch the water to make a splash, and the louder the tuning fork, the bigger the splash; the paper cone will vibrate when the loudspeaker makes a sound and the louder the sound, the bigger the vibration. According to the above phenomenon can be summarized: (1) the sound is generated by the vibration of the object; (2) the size of the sound with the amplitude of the sound emitter.

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4. Tone: determined by the object itself. People are able to recognize musical instruments or distinguish people according to their timbre.

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5. Distinguish between the three elements of music: hear the sound of people - based on the tone of different people to determine; shouting - refers to the loudness; soprano singer - refers to the pitch.

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Four, the hazards of noise and control

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1. Contemporary society's four major pollution: noise pollution, water pollution, air pollution, solid waste pollution.

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2. Physics point of view, noise is a sound emitted by the sound emitting body to do irregular and chaotic vibration; environmental protection point of view noise is a sound that prevents people from resting, studying and working normally, as well as the sound of people to listen to the sound of the role of the sound of interference.

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3. People use decibels (dB) to divide the sound level; the lower limit of hearing 0dB; in order to protect hearing should control the noise does not exceed 90dB; in order to ensure that the work and study, the noise should be controlled not more than 70dB; in order to ensure that the rest and sleep should be controlled noise does not exceed 50dB.

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4. Weakening of the noise methods: in the source of the sound, in the propagation process to reduce the noise. Weakening, weakening in the process of propagation, weakening in the human ear.

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V. Utilization of sound

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Breakthrough:

1. Someone yelled at a dry well, after 0.2s after the echo was heard, ask the dry well about how deep it is?

2. As shown in Figure 3, an energized small bell is placed in a glass enclosure connected to an extractor, answer the following questions:

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Figure 3

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(1) The air inside the glass enclosure is gradually drawn out with the extractor, and it will be found that ?0?2?0.2?0.2?0.2?0.2?0.2?2.2.0?0? 2?0?2?0?2?0?2?0?2?0?2?0?2?0?2?0?2?0?2?0?2?0?2?0?2?0?2?0?2?0?2?0?2?0?2?0?2?0.2 .

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0?2 3. In Figure 4, Xiaoming and Xiaogang made a "clay telephone" by connecting two paper cups with fine cotton thread.

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(1) They were able to make a call between l0m with the "clay phone", which shows that the "0?2 ?0?2?0?2?0?2?0?2?0?2?0?2?0?2?0.0?0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.2.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0. 0?2?0?2?0?2?0?2?0?2?0?2?0?2?0?2?0?2?0?2?0?2?0?2?0?0?2?0?2?0?2?0?2.

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(2) At the same distance from each other, the speaker spoke at the same loudness, and the sound was heard louder if a thin wire was connected to the clay telephone instead. 这一实验现象表明：?0?2?0?2?0?2?0?2?0?2?0?2?0?2?0?2?0?2?0?2?0?2?0?2?0?2?0?2?0?2?0?2?0?2?0?2?0?2?0?2?0?2?0?2?0?2?0?2?0?2?0?2?0?2?0?2 。

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(3) If another student pinches a part of the line with his hand while using a clay phone, the listening party cannot hear the sound due to the fact that ?0?2?0?2?0?2?0?2?0?2?0.0?2.0?2.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0. ?2?0?2?0?2?0?2?0?2?0?2?0?2?0?2?0?2?0?2?0?2?0?2?0?2.

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(4) If the cord is not straightened but is in a loose position when the earth telephone is used, the party who is listening passes the cotton cord ?0?2?0?2?0?2?0.0?2?0.0?2.0?2.0.0?2.0.0?2.0.0.2.0.0?2 (optional) "can" or "cannot") hear the other person.

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4. As shown in Figure 5, gently bite the upper end of the pencil with your teeth, tap the lower end of the pencil with your finger, and listen to the sound of this tap, then open your mouth so that your teeth don't touch the pencil, and tap the lower end of the pencil with your finger with the same force as before, and compare the sound you hear on these two occasions, and differentiate between the two sounds:

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Figure 5

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(1) The most important difference between these two sounds is that they are not identical. The most important difference between the two sounds is?0?2?0?2?0?2?0?2?0?2?0?2?0?2?0?2?0?2?0?2 is different (choose: pitch, loudness, timbre).

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(2) What do you think you learned from this experiment? Answer: ?0?2?0?2?0?2?0?2?0?2?0?2?0?2?0?2?0?2?0?2?0.

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