A sound wave (sound vibrations) is a mechanical vibration of the molecules of a substance (for example, air) transmitted in space.
But not every oscillating body is a source of sound. For example, an oscillating weight suspended on a thread or spring does not make a sound. A metal ruler will also stop sounding if you move it up in a vise and thereby lengthen the free end so that its oscillation frequency becomes less than 20 Hz. Studies have shown that the human ear is able to perceive as sound the mechanical vibrations of bodies occurring at a frequency of 20 Hz to 20,000 Hz. Therefore, vibrations whose frequencies are in this range are called sound. Mechanical vibrations whose frequency exceeds 20,000 Hz are called ultrasonic, and vibrations with frequencies less than 20 Hz are called infrasonic. It should be noted that the indicated boundaries of the sound range are arbitrary, since they depend on the age of people and individual features their hearing aid. Usually, with age, the upper frequency limit of perceived sounds decreases significantly - some older people can hear sounds with frequencies not exceeding 6000 Hz. Children, on the contrary, can perceive sounds whose frequency is slightly more than 20,000 Hz. Oscillations whose frequencies are greater than 20,000 Hz or less than 20 Hz are heard by some animals. The world is filled with a wide variety of sounds: the ticking of clocks and the rumble of motors, the rustling of leaves and the howling of the wind, the singing of birds and the voices of people. About how sounds are born, and what they represent, people began to guess a very long time ago. They noticed, for example, that sound is created by bodies vibrating in the air. Even the ancient Greek philosopher and scientist-encyclopedist Aristotle, based on observations, correctly explained the nature of sound, believing that the sounding body creates alternate compression and rarefaction of air. Thus, an oscillating string now compresses, then rarefies the air, and due to the elasticity of the air, these alternating influences are transmitted further into space - from layer to layer, elastic waves arise. Reaching our ear, they act on the eardrums and cause the sensation of sound. By ear, a person perceives elastic waves having a frequency ranging from about 16 Hz to 20 kHz (1 Hz - 1 oscillation per second). In accordance with this, elastic waves in any medium whose frequencies lie within the indicated limits are called sound waves or simply sound. In air at a temperature of 0 ° C and normal pressure, sound propagates at a speed of 330 m / s, in sea water- about 1500 m / s, in some metals the speed of sound reaches 7000 m / s. Elastic waves with a frequency of less than 16 Hz are called infrasound, and waves whose frequency exceeds 20 kHz are called ultrasound.
The source of sound in gases and liquids can be not only vibrating bodies. For example, a bullet and an arrow whistle in flight, the wind howls. And the roar of a turbojet aircraft consists not only of the noise of operating units - a fan, compressor, turbine, combustion chamber, etc., but also of the noise of a jet stream, vortex, turbulent air flows that occur when the aircraft flows around at high speeds. A body rapidly rushing through the air or water, as it were, breaks the flow around it, periodically generates areas of rarefaction and compression in the medium. The result is sound waves. Sound can propagate in the form of longitudinal and transverse waves. In a gaseous and liquid medium, only longitudinal waves arise, when the oscillatory motion of particles occurs only in the direction in which the wave propagates. IN solids in addition to longitudinal waves, transverse waves also arise when the particles of the medium oscillate in directions perpendicular to the direction of wave propagation. There, striking the string perpendicular to its direction, we make the wave run along the string. The human ear is not equally receptive to sounds of different frequencies. It is most sensitive to frequencies from 1000 to 4000 Hz. At very high intensity, the waves are no longer perceived as sound, causing a feeling of pressing pain in the ears. The intensity of the sound waves at which this happens is called the pain threshold. The concepts of tone and timbre of sound are also important in the study of sound. Any real sound, whether it be a human voice or the playing of a musical instrument, is not a simple harmonic oscillation, but a kind of mixture of many harmonic vibrations with a certain set of frequencies. The one with the lowest frequency is called the fundamental tone, the others are overtones. A different number of overtones inherent in a particular sound gives it a special color - timbre. The difference between one timbre and another is due not only to the number, but also to the intensity of the overtones that accompany the sound of the fundamental tone. By timbre, we can easily distinguish the sounds of the violin and piano, guitar and flute, we recognize the voices of familiar people.
- Oscillation frequency called the number of complete oscillations per second. The unit of frequency is 1 hertz (Hz). 1 hertz corresponds to one full (in one and the other direction) oscillation occurring in one second.
- Period called the time (s) during which one complete oscillation occurs. The higher the oscillation frequency, the shorter their period, i.e. f=1/T. Thus, the frequency of oscillations is greater, the shorter their period, and vice versa. The human voice creates sound vibrations with a frequency of 80 to 12,000 Hz, and hearing perceives sound vibrations in the range of 16-20,000 Hz.
- Amplitude oscillations are called the greatest deviation of an oscillating body from its original (calm) position. The larger the oscillation amplitude, the louder sound. The sounds of human speech are complex sound vibrations, consisting of one or another number of simple vibrations, different in frequency and amplitude. Each sound of speech has only its own combination of vibrations of different frequencies and amplitudes. Therefore, the form of vibrations of one sound of speech differs markedly from the form of another, which shows the graphs of vibrations during the pronunciation of the sounds a, o and y.
A person characterizes any sounds in accordance with his perception in terms of volume and height.
Let's move on to the consideration of sound phenomena.
The world of sounds surrounding us is diverse - the voices of people and music, the singing of birds and the buzzing of bees, thunder during a thunderstorm and the noise of the forest in the wind, the sound of passing cars, planes and other objects.
Pay attention!
Sound sources are vibrating bodies.
Example:
We fix an elastic metal ruler in a vise. If its free part, the length of which is chosen in a certain way, is brought into oscillatory motion, then the ruler will make a sound (Fig. 1).
Thus, the oscillating ruler is the source of the sound.
Consider the image of a sounding string, the ends of which are fixed (Fig. 2). The blurred outlines of this string and the apparent thickening in the middle indicate that the string is vibrating.
If you bring the end of the paper strip closer to the sounding string, then the strip will bounce from the shocks of the string. As long as the string vibrates, a sound is heard; stop the string, and the sound stops.
Figure 3 shows a tuning fork - a curved metal rod on a leg, which is mounted on a resonator box.
If you hit the tuning fork with a soft hammer (or draw a bow over it), then the tuning fork will sound (Fig. 4).
We bring a light ball (a glass bead) suspended on a thread to a sounding tuning fork - the ball will bounce off the tuning fork, indicating vibrations of its branches (Fig. 5).
In order to “record” vibrations of a tuning fork with a small (of the order of \(16\) Hz) natural frequency and a large oscillation amplitude, a thin and narrow metal strip with a tip at the end can be screwed to the end of one of its branches. The tip must be bent down and lightly touch it with a smoked glass plate lying on the table. When the plate moves quickly under the oscillating branches of the tuning fork, the tip leaves a mark on the plate in the form of a wavy line (Fig. 6).
The wavy line drawn on the plate with a tip is very close to a sinusoid. Thus, we can assume that each branch of the sounding tuning fork performs harmonic oscillations.
Various experiments show that any source of sound necessarily oscillates, even if these oscillations are imperceptible to the eye. For example, the sounds of the voices of people and many animals arise as a result of their vibrations. vocal cords, the sound of wind musical instruments, the sound of a siren, the whistle of the wind, the rustle of leaves, the peals of thunder are due to fluctuations in air masses.
Pay attention!
Not every vibrating body is a source of sound.
For example, a vibrating weight suspended on a thread or spring does not make a sound. A metal ruler will also stop sounding if its free end is lengthened so that the frequency of its oscillations becomes less than \ (16 \) Hz.
The human ear is capable of perceiving as sound mechanical vibrations with a frequency ranging from \(16\) to \(20,000\) Hz (usually transmitted through air).
Mechanical vibrations, the frequency of which lies in the range from \(16\) to \(20000\) Hz, are called sound.
The indicated boundaries of the sound range are conditional, as they depend on the age of people and the individual characteristics of their hearing aid. Usually, with age, the upper frequency limit of perceived sounds decreases significantly - some elderly people can hear sounds with frequencies not exceeding \(6000\) Hz. Children, on the contrary, can perceive sounds whose frequency is slightly higher than \ (20,000 \) Hz.
Mechanical vibrations whose frequency exceeds \(20,000\) Hz are called ultrasonic, and vibrations with frequencies less than \(16\) Hz are called infrasonic.
Ultrasound and infrasound are as widespread in nature as the sound waves. They are emitted and used for their "negotiations" by dolphins, bats and some other living creatures.
fluctuations- These are movements or processes that are characterized by a certain repetition in time.
Oscillation period Tis the time interval during which one complete oscillation occurs.
Oscillation frequency is the number of complete oscillations per unit time. In the SI system, it is expressed in hertz (Hz).
The period and frequency of oscillations are related by the relation
Harmonic vibrations- these are oscillations in which the oscillating value changes according to the law of sine or cosine. The offset is determined by the formula
Amplitude (a), period (b) and phase of oscillations(from) two oscillating bodies
mechanical waves
waves called periodic perturbations that propagate in space over time. Waves are divided into longitudinal and transverse.
Elastic waves in the air that cause auditory sensations in a person are called sound waves or simply sound. The audio frequency range is from 20 Hz to 20 kHz. Waves with a frequency of less than 20 Hz are called infrasound, those with a frequency of more than 20 kHz are called ultrasound. The presence of any elastic medium for sound transmission is mandatory.
The loudness of a sound is determined by the intensity of the sound wave, that is, the energy carried by the wave per unit time.
Sound pressure depends on the amplitude of the pressure fluctuations in the sound wave.
The pitch of the sound (tone) is determined by the frequency of vibrations. The low male voice (bass) range is approximately 80 to 400 Hz. The range of a high female voice (soprano) is from 250 to 1050 Hz.
In technology and the world around us, we often have to deal with periodical(or almost periodic) processes that repeat at regular intervals. Such processes are called oscillatory.
Vibrations are one of the most common processes in nature and technology. Wings of insects and birds in flight, high-rise buildings and high-voltage wires under the action of the wind, the pendulum of a wound clock and a car on springs during movement, the level of the river during the year and the temperature of the human body during illness, sound is fluctuations in air density and pressure, radio waves - periodic changes in the strength of the electric and magnetic fields, visible light is also electromagnetic oscillations, only with slightly different wavelength and frequency, earthquakes - vibrations of the soil, pulse beats - periodic contractions of the human heart muscle, etc.
Vibrations are mechanical, electromagnetic, chemical, thermodynamic and various others. Despite this diversity, they all have much in common.
Oscillatory phenomena of various physical nature are subject to general laws. For example, current fluctuations in electrical circuit and fluctuations mathematical pendulum can be described by the same equations. The generality of oscillatory regularities makes it possible to consider oscillatory processes different nature from a single point of view. sign oscillatory motion is his periodicity.
Mechanical vibrations -thismovements that repeat exactly or approximately at regular intervals.
Examples of simple oscillatory systems are a weight on a spring (spring pendulum) or a ball on a thread (mathematical pendulum).
During mechanical vibrations, the kinetic and potential energies change periodically.
At maximum deviation body from the equilibrium position, its speed, and consequently, and kinetic energy goes to zero. In this position potential energy oscillating body reaches the maximum value. For a load on a spring, the potential energy is the energy of the elastic deformation of the spring. For a mathematical pendulum, this is the energy in the Earth's gravitational field.
When a body in its motion passes through equilibrium position, its speed is maximum. The body skips the equilibrium position according to the law of inertia. At this moment it has maximum kinetic and minimum potential energy. An increase in kinetic energy occurs at the expense of a decrease in potential energy.
With further movement, the potential energy begins to increase due to the decrease in kinetic energy, etc.
Thus, with harmonic vibrations, there is a periodic transformation of kinetic energy into potential energy and vice versa.
If there is no friction in the oscillatory system, then the total mechanical energy during mechanical vibrations remains unchanged.
For spring load:
In the position of maximum deflection, the total energy of the pendulum is equal to the potential energy of the deformed spring:
When passing through the equilibrium position, the total energy is equal to the kinetic energy of the load:
For small oscillations of a mathematical pendulum:
In the position of maximum deviation, the total energy of the pendulum is equal to the potential energy of the body raised to a height h:
When passing through the equilibrium position, the total energy is equal to the kinetic energy of the body:
Here h m is the maximum lifting height of the pendulum in the Earth's gravitational field, x m and υ m = ω 0 x m are the maximum deviations of the pendulum from the equilibrium position and its velocity.
Harmonic oscillations and their characteristics. Equation of harmonic oscillation.
The simplest type of oscillatory process are simple harmonic vibrations, which are described by the equation
x = x m cos(ω t + φ 0).
Here x- displacement of the body from the equilibrium position,
x m- the amplitude of oscillations, that is, the maximum displacement from the equilibrium position,
ω – cyclic or circular frequency hesitation,
t- time.
Characteristics of oscillatory motion.
Offset x - deviation of the oscillating point from the equilibrium position. The unit of measurement is 1 meter.
Oscillation amplitude A - the maximum deviation of the oscillating point from the equilibrium position. The unit of measurement is 1 meter.
Oscillation periodT- the minimum time interval for which one complete oscillation occurs is called. The unit of measurement is 1 second.
where t is the oscillation time, N is the number of oscillations made during this time.
According to the graph of harmonic oscillations, you can determine the period and amplitude of oscillations:
Oscillation frequency ν – a physical quantity equal to the number of oscillations per unit of time.
Frequency is the reciprocal of the oscillation period:
Frequency oscillations ν shows how many oscillations occur in 1 s. The unit of frequency is hertz(Hz).
Cyclic frequency ω is the number of oscillations in 2π seconds.
The oscillation frequency ν is related to cyclic frequency ω and oscillation period T ratios:
Phase harmonic process - a value that is under the sign of sine or cosine in the equation of harmonic oscillations φ = ω t+ φ 0 . At t= 0 φ = φ 0 , therefore φ 0 called initial phase.
Graph of harmonic oscillations is a sine wave or a cosine wave.
In all three cases for the blue curves φ 0 = 0:
only greater amplitude(x" m > x m);
the red curve is different from the blue one only meaning period(T" = T / 2);
the red curve is different from the blue one only meaning initial phase(glad).
When the body oscillates along a straight line (axis OX) the velocity vector is always directed along this straight line. The speed of the body is determined by the expression
In mathematics, the procedure for finding the limit of the ratio Δx / Δt at Δ t→ 0 is called the calculation of the derivative of the function x(t) by time t and is denoted as x"(t).The speed is equal to the derivative of the function x( t) by time t.
For the harmonic law of motion x = x m cos(ω t+ φ 0) the calculation of the derivative leads to the following result:
υ X =x"(t)= ω x m sin(ω t + φ 0)
Acceleration is defined in a similar way a x bodies under harmonic vibrations. Acceleration a is equal to the derivative of the function υ( t) by time t, or the second derivative of the function x(t). The calculations give:
a x \u003d υ x "(t) =x""(t)= -ω 2 x m cos(ω t+ φ 0)=-ω 2 x
The minus sign in this expression means that the acceleration a(t) always has the opposite sign of the offset x(t), and, therefore, according to Newton's second law, the force that causes the body to perform harmonic oscillations is always directed towards the equilibrium position ( x = 0).
The figure shows graphs of the coordinates, velocity and acceleration of a body that performs harmonic oscillations.
Graphs of coordinate x(t), velocity υ(t) and acceleration a(t) of a body performing harmonic oscillations.
Spring pendulum.
Spring pendulumcalled a load of some mass m, attached to a spring of stiffness k, the second end of which is fixed motionless.
natural frequencyω 0 free vibrations of the load on the spring is found by the formula:
Period T harmonic vibrations of the load on the spring is equal to
This means that the period of oscillation of a spring pendulum depends on the mass of the load and on the stiffness of the spring.
Physical properties of the oscillatory system determine only the natural oscillation frequency ω 0 and the period T . Such parameters of the oscillation process as amplitude x m And initial phaseφ 0 , are determined by the way in which the system was brought out of equilibrium at the initial moment of time.
Mathematical pendulum.
Mathematical pendulumcalled a small body suspended on a thin inextensible thread, the mass of which is negligible compared to the mass of the body.
In the equilibrium position, when the pendulum hangs on a plumb line, the gravity force is balanced by the thread tension force N. When the pendulum deviates from the equilibrium position by a certain angle φ, a tangential component of the gravity force appears F τ = – mg sin phi. The minus sign in this formula means that the tangential component is directed in the direction opposite to the pendulum deflection.
Mathematical pendulum.φ - angular deviation of the pendulum from the equilibrium position,
x= lφ – displacement of the pendulum along the arc
The natural frequency of small oscillations of a mathematical pendulum is expressed by the formula:
Oscillation period of a mathematical pendulum:
This means that the period of oscillation of a mathematical pendulum depends on the length of the thread and on the acceleration of free fall of the area where the pendulum is installed.
Free and forced vibrations.
Mechanical oscillations, like oscillatory processes of any other physical nature, can be free And forced.
Free vibrations -These are oscillations that occur in the system under the action of internal forces, after the system has been brought out of a position of stable equilibrium.
The oscillations of a weight on a spring or the oscillations of a pendulum are free oscillations.
In real conditions, any oscillatory system is under the influence of friction forces (resistance). At the same time, part mechanical energy is converted into the internal energy of the thermal motion of atoms and molecules, and the vibrations become fading.
Decaying called vibrations, the amplitude of which decreases with time.
In order for the oscillations not to damp, it is necessary to impart additional energy to the system, i.e. act on the oscillatory system with a periodic force (for example, to swing a swing).
Oscillations that occur under the influence of an external periodically changing force are calledforced.
The external force performs positive work and provides an influx of energy to the oscillatory system. It does not allow oscillations to fade, despite the action of friction forces.
A periodic external force can vary in time according to various laws. Of particular interest is the case when an external force, changing according to a harmonic law with a frequency ω, acts on an oscillatory system capable of performing natural oscillations at a certain frequency ω 0 .
If free vibrations occur at a frequency ω 0 , which is determined by the parameters of the system, then steady forced oscillations always occur on frequency ω of the external force .
The phenomenon of a sharp increase in the amplitude of forced oscillations when the frequency of natural oscillations coincides with the frequency of the external driving force is calledresonance.
Amplitude dependence x m forced oscillations from the frequency ω of the driving force is called resonant characteristic or resonance curve.
Resonance curves at various damping levels:
1 - oscillatory system without friction; at resonance, the amplitude x m of forced oscillations increases indefinitely;
2, 3, 4 - real resonance curves for oscillatory systems with different friction.
In the absence of friction, the amplitude of forced oscillations at resonance should increase indefinitely. In real conditions, the amplitude of steady-state forced oscillations is determined by the condition: the work of an external force during the period of oscillations must be equal to the loss of mechanical energy over the same time due to friction. The less friction, the greater the amplitude of forced oscillations at resonance.
The phenomenon of resonance can cause the destruction of bridges, buildings and other structures, if the natural frequencies of their oscillations coincide with the frequency periodically operating force caused, for example, by the rotation of an unbalanced motor.
Sound- These are elastic longitudinal waves with a frequency from 20 Hz to 20,000 Hz, which cause auditory sensations in a person.
Sound source- various oscillating bodies, such as a tightly stretched string or a thin steel plate, clamped on one side.
How do oscillatory movements occur? It is enough to pull and release the string of a musical instrument or a steel plate clamped at one end in a vise, as they will make a sound. Vibrations of a string or metal plate transferred to the surrounding air. When the plate deviates, for example, to the right, it compresses (compresses) the layers of air adjacent to it on the right; in this case, the layer of air adjacent to the plate on the left side will be rarefied. When the plate deviates to the left side, it compresses the air layers on the left and rarefies the air layers adjacent to it on the right side, etc. The compression and rarefaction of the air layers adjacent to the plate will be transferred to the neighboring layers. This process will be repeated periodically, gradually weakening, until the oscillations completely stop.
Thus, the vibrations of a string or a plate excite vibrations of the surrounding air and, spreading, reach the ear of a person, causing his eardrum to vibrate, causing irritation of the auditory nerve, which we perceive as sound.
Sound Wave Velocity in different environments not the same. It depends on the elasticity of the medium in which they propagate. Sound travels slowest in gases. In air, the speed of propagation of sound vibrations is on average 330 m / s, however, it can vary depending on its humidity, pressure and temperature. Sound does not propagate in airless space. Sound travels faster in liquids. In solids - even faster. In a steel rail, for example, sound propagates at a speed of » 5000 m/s.
At dissemination sound into atoms and molecules vibrate along direction of wave propagation, then the sound - longitudinal wave.
SOUND CHARACTERISTICS
1. Volume. The loudness depends on the amplitude of the vibrations in the sound wave. Volume sound is determined amplitude waves.
The unit of sound volume is 1 Bel (in honor of Alexander Graham Bell, the inventor of the telephone). The loudness of a sound is 1 B if its power is 10 times the threshold of audibility.
In practice, loudness is measured in decibels (dB).
1 dB = 0.1B. 10 dB - whisper; 20–30 dB - noise standard in residential premises;
50 dB - conversation of medium volume;
70 dB - typewriter noise;
80 dB - the noise of a running truck engine;
120 dB - noise of a working tractor at a distance of 1 m
130 dB - pain threshold.
Sound above 180 dB can even cause a rupture of the eardrum.
2. Pitch. Height sound is determined frequency waves, or the frequency of vibration of the sound source.
- bass - 80-350 Hz,
- baritone - 110-149 Hz,
- tenor - 130-520 Hz,
- treble - 260–1000 Hz,
- soprano - 260-1050 Hz,
- coloratura soprano - up to 1400 Hz.
The human ear is able to perceive elastic waves with a frequency of approximately from 16 Hz to 20 kHz. How do we hear?
Human auditory analyzer - ear- consists of four parts:
outer ear
The outer ear includes the auricle, ear canal, and the tympanic membrane, which covers the inner end of the ear canal. The ear canal has an irregular curved shape. In an adult, it is about 2.5 cm long and about 8 mm in diameter. The surface of the ear canal is covered with hairs and contains glands that secrete earwax, which is necessary to maintain skin moisture. The auditory meatus also provides a constant temperature and humidity of the tympanic membrane.
Middle ear
The middle ear is an air-filled cavity behind the eardrum. This cavity connects to the nasopharynx through the Eustachian tube, a narrow cartilaginous canal that is usually closed. Swallowing opens the Eustachian tube, which allows air to enter the cavity and equalize pressure on both sides of the eardrum for optimal mobility. The middle ear contains three miniature auditory ossicles: the malleus, anvil, and stirrup. One end of the malleus is connected to the tympanic membrane, its other end is connected to the anvil, which, in turn, is connected to the stirrup, and the stirrup to the cochlea of the inner ear. The tympanic membrane constantly oscillates under the influence of sounds caught by the ear, and the auditory ossicles transmit its vibrations to the inner ear.
inner ear
The inner ear contains several structures, but only the cochlea, which gets its name from its spiral shape, is relevant to hearing. The cochlea is divided into three channels filled with lymphatic fluids. The fluid in the middle channel differs in composition from the fluid in the other two channels. The organ directly responsible for hearing (the organ of Corti) is located in the middle canal. The organ of Corti contains about 30,000 hair cells, which pick up fluctuations in the fluid in the canal caused by the movement of the stirrup and generate electrical impulses that are transmitted along the auditory nerve to the auditory cortex of the brain. Each hair cell responds to a specific sound frequency, with high frequencies picked up by cells in the lower part of the cochlea, and cells tuned to low frequencies are located in the upper part of the cochlea. If the hair cells die for any reason, the person ceases to perceive the sounds of the corresponding frequencies.
auditory pathways
Auditory pathways are a collection of nerve fibers that conduct nerve impulses from the cochlea to the auditory centers of the cerebral cortex, resulting in an auditory sensation. The auditory centers are located in the temporal lobes of the brain. The time taken for the auditory signal to travel from the outer ear to the auditory centers of the brain is about 10 milliseconds.
Sound perception
The ear sequentially converts sounds into mechanical vibrations of the tympanic membrane and auditory ossicles, then into vibrations of the fluid in the cochlea, and finally into electrical impulses, which are transmitted along the pathways of the central auditory system to the temporal lobes of the brain for recognition and processing.
The brain and intermediate nodes of the auditory pathways extract not only information about the pitch and loudness of the sound, but also other characteristics of the sound, for example, the time interval between the moments when the sound is picked up by the right and left ears - this is the basis for the ability of a person to determine the direction in which the sound comes. At the same time, the brain evaluates both the information received from each ear separately and combines all the information received into a single sensation.
Our brains store patterns for the sounds around us—familiar voices, music, dangerous sounds, and so on. This helps the brain in the process of processing information about sound to quickly distinguish familiar sounds from unfamiliar ones. With hearing loss, the brain begins to receive distorted information(sounds become quieter), which leads to errors in the interpretation of sounds. On the other hand, brain damage due to aging, head injury, or neurological diseases and disorders may be accompanied by symptoms similar to those of hearing loss, such as inattention, detachment from the environment, inadequate response. In order to correctly hear and understand sounds, the coordinated work of the auditory analyzer and the brain is necessary. Thus, without exaggeration, we can say that a person hears not with his ears, but with his brain!
Animals perceive waves of other frequencies as sound.
Ultrasound - longitudinal waves with a frequency exceeding 20,000 Hz.
The use of ultrasound.
With the help of sonars installed on ships, they measure the depth of the sea, detect schools of fish, an oncoming iceberg or a submarine.
Ultrasound is used in industry to detect defects in products.
In medicine, using ultrasound, bones are welded, tumors are detected, and diseases are diagnosed.
The biological effect of ultrasound allows it to be used for sterilizing milk, medicinal substances, and medical instruments.
Bats and dolphins have perfect ultrasonic locators.
Physics test Mechanical vibrations and waves Sound for grade 9 students with answers. The test includes 2 options, each with 12 tasks.
1 option
1. With free vibrations, the ball on the thread travels from the extreme left position to the extreme right position in 0.1 s. Determine the period of oscillation of the ball.
1) 0.1 s
2) 0.2 s
3) 0.3 s
4) 0.4 s
2. The figure shows the dependence of the coordinate of the center of a ball suspended on a spring from time to time. The oscillation frequency is
1) 0.25 Hz
2) 0.5Hz
3) 2Hz
4) 4Hz
3. How many complete oscillations does material point for 10 s, if the oscillation frequency is 220 Hz?
1) 22
2) 88
3) 440
4) 2200
4. In what directions does a longitudinal wave oscillate?
1) In all directions
5. The distance between the nearest wave crests in the sea is 6 m. What is the period of wave impacts on the hull of the boat if their speed is 3 m/s?
1) 0.5 s
2) 2 s
3) 12 s
4) 32 s
6. The man heard the sound of thunder 10 seconds after the flash of lightning. Determine the speed of sound in air if lightning struck at a distance of 3.3 km from the observer.
1) 0.33 m/s
2) 33 m/s
3) 330 m/s
4) 33 km/s
7. In what medium do sound waves travel at the lowest speed?
1) In solids
2) In liquids
3) In gases
4) Everywhere is the same
8. What are mechanical vibrations whose frequency is less than 20 Hz called?
1) Sound
2) Ultrasonic
3) Infrasonic
9. Determine the length of the sound wave in air if the frequency of the sound source is 200 Hz. The speed of sound in air is 340 m/s.
1) 1.7 m
2) 0.59 m
3) 540 m
4) 68,000 m
10. How will the length of a sound wave change when the frequency of its source oscillations decreases by 2 times?
1) will increase by 2 times
2) Decrease by 2 times
3) Will not change
4) Decrease by 4 times
11. The upper limit of the oscillation frequency perceived by the human ear is 22 kHz for children, and 10 kHz for the elderly. In air, the speed of sound is 340 m/s. Sound with a wavelength of 20 mm
1) only a child will hear
2) only an elderly person will hear
3) both the child and the elderly will hear
4) neither the child nor the elderly will hear
12. The echo caused by a weapon shot reached the shooter 2 s after the shot. Determine the distance to the obstacle from which the reflection occurred if the speed of sound in air is 340 m/s.
1) 170 m
2) 340 m
3) 680 m
4) 1360 m
Option 2
1. With free vibrations, the ball on the thread travels from the extreme left position to the equilibrium position in 0.2 s. What is the period of the ball's oscillation?
1) 0.2 s
2) 0.4 s
3) 0.6 s
4) 0.8 s
2. The figure shows the dependence of the coordinate of the center of a ball suspended on a spring from time to time. The oscillation amplitude is
1) 10cm
2) 20cm
3) -10 cm
2) -20cm
3. When measuring a person's pulse, 150 blood pulsations were recorded in 2 minutes. Determine the frequency of contraction of the heart muscle.
1) 0.8 Hz
2) 1Hz
3) 1.25Hz
4) 75Hz
4. In what directions does a transverse wave oscillate?
1) In all directions
2) Along the direction of wave propagation
3) Perpendicular to the direction of wave propagation
4) Both in the direction of wave propagation and perpendicular to wave propagation
5. A wave with a frequency of 4 Hz propagates along the cord at a speed of 6 m/s. The wavelength is
1) 0.75 m
2) 1.5 m
3) 24 m
4) there is not enough data to solve
6. How will the wavelength change when the oscillation frequency of its source decreases by 2 times?
1) will increase by 2 times
2) Decrease by 2 times
3) Will not change
4) Decrease by 4 times
7. In what medium do sound waves not propagate?
1) In solids
2) In liquids
3) In gases
4) In a vacuum
8. What are mechanical vibrations whose frequency exceeds 20,000 Hz called?
1) Sound
2) Ultrasonic
3) Infrasonic
4) None of the answers are correct
9. The tuning fork emits a sound wave 0.5 m long. The speed of sound is 340 m/s. What is the frequency of the tuning fork?
1) 17Hz
2) 680Hz
3) 170Hz
4) 3400Hz
10. The human ear can perceive sounds with frequencies ranging from 20 Hz to 20,000 Hz. What range of wavelengths corresponds to the interval of audibility of sound vibrations? Take the speed of sound in air equal to 340 m/s.
1) From 20 m to 20,000 m
2) From 6800 m to 6,800,000 m
3) From 0.06m to 58.8m
4) From 0.017m to 17m
11. What changes does a person notice in sound with an increase in the amplitude of oscillations in a sound wave?
1) Pitch up
2) Lowering the pitch
3) Volume Up
4) Volume down
12. How far is the iceberg from the ship if the ultrasonic signal sent by the sonar was received back after 4 s? The speed of ultrasound in water is taken equal to 1500 m/s.
1) 375 m
2) 750 s
3) 3000 m
4) 6000 m
Answers to the test in physics Mechanical vibrations and waves Sound
1 option
1-2
2-1
3-4
4-2
5-2
6-3
7-3
8-3
9-1
10-1
11-1
12-2
Option 2
1-4
2-1
3-3
4-3
5-2
6-1
7-4
8-2
9-2
10-4
11-3
12-3
