Summary of knowledge about sound phenomena
1. The occurrence of sound: produced by the vibration of objects. The vibrations stopped and the sound production stopped.
2． Propagation of sound: Sound propagates through media. Sound cannot travel through a vacuum. Usually the sound we hear comes from the air.
3. Speed ??of sound: The propagation speed in air is: 340 meters/second. Sound travels faster in solids than in liquids, and in liquids it travels faster than in air.
4． Measurable distance using echo: S=1/2vt
5. There are three characteristics of musical sound: pitch, loudness, and timbre. (1) Pitch: refers to the pitch of the sound, which is related to the frequency of the sound emitter. (2) Loudness: refers to the size of the sound, which is related to the amplitude of the sound source and the distance between the sound source and the listener.
6. Ways to weaken noise: (1) weaken at the sound source; (2) weaken during the propagation process; (3) weaken at the human ear.
7． Audible sound: sound waves with a frequency between 20Hz and 20,000Hz: Ultrasound: sound waves with a frequency higher than 20,000Hz; infrasound: sound waves with a frequency lower than 20Hz.
8. Ultrasonic characteristics: good directionality, strong penetration ability, and concentrated sound energy. Specific applications include: sonar, B-ultrasound, ultrasonic velocity detector, ultrasonic cleaner, ultrasonic welder, etc.
9． Characteristics of infrasound waves: they can travel far, easily bypass obstacles, and are pervasive. Infrasound waves of a certain intensity can cause harm to the human body and even damage machinery and buildings. It is mainly produced by volcanic eruptions, tsunamis and earthquakes in nature. In addition, infrasound waves can also be produced by human-made rocket launches, aircraft flights, trains and cars, and nuclear explosions.
Example 1: Which of the following statements about sound is correct ()
A. The sound of a violin can be distinguished because its tones are different
B .Hearing the school bell shows that sound can travel in the air
C. As long as the object is vibrating, we can hear the sound
D. Building sound insulation walls next to elevated roads is Reduce noise at the sound source
Answer: B
Analysis: The sound produced by each musical instrument has a unique timbre. The ability to distinguish musical instruments based on their sound depends on the timbre of the sound they produce. Different, item A is wrong; the propagation of sound requires a medium, and sound cannot be transmitted in a vacuum. Most of the sounds heard in life are transmitted through the air. Item B is correct; the vibration of objects can make sound, but can we hear the sound? It also depends on factors such as whether the pitch of the sound is within the human hearing frequency range, whether there is a medium for transmitting sound between the person and the sound source, and whether the loudness of the sound is loud enough. Item C is wrong; building a sound insulation wall next to an elevated road is transmitting The noise is reduced during the process, and item D is wrong.
Example 2 Regarding the description of acoustic phenomena, which of the following statements is correct ()
A. The intensity of the sound is determined by the frequency of the sound source's vibration
B. The propagation speed of sound in vacuum is 340m/s
C. The hearing frequency range of the human ear is 20Hz-2000Hz
D. Turning down the volume when dancing square dance late at night is to reduce the noise at the sound source
Answer: D
Analysis: The strength of the sound, that is, the loudness, is determined by the amplitude of the vibration of the sound source. , item A is wrong; the propagation of sound requires a medium, and vacuum cannot transmit sound, item B is wrong; the hearing frequency of the human ear is 20Hz-20000Hz, item C is wrong; turning down the volume of the sound is to control the loudness of its sound, yes Attenuates noise at the source.
Example 3: There is a "lonely" whale in the North Pacific. In the past 20 years, scientists have discovered that it has been emitting a 52Hz sound to call its companions but has received no response because the vocal frequency of similar whales Usually 17~18Hz.
Which of the following statements is wrong ()
A. The sound heard by scientists comes from water as the medium
B. The sounds emitted by normal whales of the same species are infrasound waves
C. This "lonely" whale did not receive a response because the loudness of its vocalization was too low
D. The vocal organs of this "lonely" whale are thinner, shorter or tighter than those of normal whales
Answer: C
Analysis: This "lonely" whale cannot It communicates with whales of the same species because the frequency of the sound it makes is too high, so it cannot be recognized by whales of the same species.
Example 4: Xiao Leng played beautiful music on the guitar at the art festival. Regarding the sound produced by the guitar, which of the following statements is correct ()
A. The sound of music is transmitted to human ears through the air
B. Changing the position of your fingers on the string can change the loudness of the sound
C. Striking the guitar strings hard can raise the pitch of the sound
D. Stirring different guitar strings can change the tone of the guitar
Answer: A
Analysis: The propagation of sound requires a medium. All the sounds we hear in our lives are transmitted through the air. If it enters the human ear, item A is correct; changing the position of the finger pressing the string can change the frequency of the string vibration, which can change the pitch of the sound produced by the string vibration, item B is wrong; plucking the guitar string forcefully can increase the amplitude of the string vibration and improve the sound quality of the string. The loudness of the sound produced by vibration, item C is wrong; different guitar strings have different thicknesses and vibrate at different frequencies, so plucking different guitar strings can change the tone of the guitar, item D is wrong. You should choose A for this question.
Example 5: The correct statement about sound phenomena is ()
A. Sound can travel in gases and liquids
B. Sound travels fastest in a vacuum
C. The ban on honking is to block the process of sound transmission
D. It can only reduce the noise by blocking the transmission of sound
Answer: A
Analysis: The propagation of sound requires a medium. Sound cannot be transmitted in a vacuum. All solids, liquids, and gases can transmit sound. Item A is correct, item B is wrong; there are three ways to reduce noise: preventing the generation of noise, blocking the spread of noise, and preventing noise from entering human ears. Banning horns is to prevent the generation of noise. Items C and D are both wrong.