first kind
First, review the introduction.
We live in a world full of sound. People exchange ideas and express their feelings through language. Beautiful music can cultivate people's temperament and give people beautiful enjoyment. Annoying noise will distract people's attention, affect work, hinder rest and even affect people's health. The phenomenon of * * * vibration of various objects and its application is one of the great discoveries of China people in acoustics. The Echo Wall, Sanyinshi and the Dome of the Temple of Heaven mentioned in the textbooks are also miracles created by ancient people in China by using the acoustic principle.
Second, basic exercises
Do the following set of fill in the blanks.
Everything that makes a sound vibrates, and the spread of sound must depend on the medium.
Sound travels faster in solids and liquids than in air, and vacuum cannot travel sound.
3. If the echo reaches the human ear more than 0. 1 second later than the original sound, the human ear can distinguish the echo from the original sound; If it is less than 0. 1 sec, the echo and the original sound are mixed together to enhance the original sound.
4. The characteristics of musical sound are: tone, loudness and timbre. Among them, the tone is related to the frequency of the speaker, and the loudness is related to the amplitude of the speaker and the distance between the sound source and the listener.
⒌ The ways of noise attenuation are: attenuation at the sound source, attenuation during propagation and attenuation at the ear.
Third, the review process: explain the basic knowledge (the teacher speaks the basics while interspersed with basic exercises);
1, sound generation:
A, the object vibration produces sound, vibration stops, the sound of the object stops, but the sound can continue to spread.
B examples of sound generated by solid vibration: knocking at the door, knocking on the table, people walking on the floor, etc. It can emit the sound of solid vibration.
C. Examples of sound generated by body vibration: the sound of sea waves generated by seawater lapping on the coast, or the huge sound of sea waves generated by the famous Qiantang River tide.
D. Examples of sound produced by gas vibration: the sound produced when bullets and shells pass through the air quickly, and the autumn wind whistling.
2. The spread of sound
A. the substance that transmits sound is called medium.
Sound transmission media include air (sound wave propagation), solid and liquid (compare the sound transmission speed and advantages and disadvantages of these substances).
B. Sound speed: it is a physical quantity indicating the speed of sound propagation, and its size is equal to the distance that sound travels per second.
The speed of sound is related to the temperature and type of matter. Generally speaking, there are V- solid >: V liquid > V gas.
In the air of 15℃, the speed of sound is 340m/s.
3. Conditions for people to hear sound: A. The sound source is vibrating to produce sound. B. There is a medium that transmits sound, such as air. C. the hearing organs are intact.
The teacher briefly described the structure of human ear, focusing on the functions of tympanic membrane (forming vibration), auditory bone (amplifying vibration), auditory nerve (transmitting nerve impulse generated by acoustic stimulation) and auditory pathway (forming hearing).
Bone conduction: human skull, jaw, etc. Can receive sound stimulation to form nerve excitement, and can conduct these excitement to the auditory pathway to form hearing.
Second lesson
I. Review process
Three characteristics of sound:
A. Tone: the level of voice, which is commonly referred to as the "tone level" problem.
① Factors that determine tone: frequency (the teacher will explain the concept and unit of frequency again)
② Human hearing range: 20 Hz ~ 20 Hz ~ 20Hz~20000Hz.
③ Ultrasonic wave: sound higher than 20000Hz. People can't hear the sound.
④ infrasound: sound below 20Hz. People can't hear the sound. Other animals can hear ultrasonic waves and infrasound waves.
B, loudness: refers to the strength (size) of sound. It is also commonly referred to as the "sound size" problem. It is determined by the amplitude of the object.
The teacher compares the differences in frequency and amplitude.
C. timbre: the unique characteristics of a certain sound. Such as erhu and violin, people can divide day and night because of their different timbres.
The third category
I. Review process
Learning this chapter requires a common sense understanding of noise and its harm and the methods to reduce it.
1. Noise:
① Physical definition: sound generated by irregular vibration of objects.
The concept of environmental protection: the sound that affects people's study, rest, work and conversation.
③ Representation of noise intensity: expressed in decibels (dB). The teacher is talking about ensuring the sound intensity level of work and study and protecting the sound intensity level of people's listening.
④ Noise control: implemented from three aspects.
Use of sound:
① Sound contains information: sound can convey information.
② Echo: echolocation
(3) Sound contains energy: ultrasonic lithotripsy, the development of acoustic energy in urban noise (under study).