Sound waves. Sound sources. Characteristics of sound (Eryutkin E. S.). Sound vibrations

Sound sources. Sound vibrations

Man lives in a world of sounds. Sound for humans is a source of information. He warns people about danger. Sound in the form of music, birdsong gives us pleasure. We enjoy listening to a person with a pleasant voice. Sounds are important not only for humans, but also for animals, for which good sound detection helps them survive.

Sound – these are mechanical elastic waves propagating in gases, liquids, and solids.

Reason for the sound - vibration (oscillations) of bodies, although these vibrations are often invisible to our eyes.

Sound sources - physical bodies, which fluctuate, i.e. tremble or vibrate at a frequency
from 16 to 20,000 times per second. The vibrating body can be solid, for example, a string
or Earth's crust, gaseous, for example, a stream of air in wind musical instruments
or liquid, for example, waves on water.

Volume

Loudness depends on the amplitude of vibrations in the sound wave. The unit of sound volume is 1 Bel (in honor of Alexander Graham Bell, the inventor of the telephone). In practice, loudness is measured in decibels (dB). 1 dB = 0.1B.

10 dB – whisper;

20–30 dB – noise standards in residential premises;
50 dB– medium volume conversation;
80 d B – the noise of a running truck engine;
130 dB– threshold pain

Sound louder than 180 dB can even cause eardrum rupture.

High sounds represented by high-frequency waves - for example, birdsong.

Low sounds These are low-frequency waves, such as the sound of a large truck engine.

Sound waves

Sound waves- These are elastic waves that cause a person to feel the sensation of sound.

A sound wave can travel a wide variety of distances. Gunfire can be heard at 10-15 km, the neighing of horses and barking dogs - at 2-3 km, and whispers only at a few meters. These sounds are transmitted through the air. But not only air can be a conductor of sound.

By placing your ear to the rails, you can hear the sound of an approaching train much earlier and at a greater distance. This means that metal conducts sound faster and better than air. Water also conducts sound well. Having dived into the water, you can clearly hear the stones knocking against each other, the noise of the pebbles during the surf.

The property of water - it conducts sound well - is widely used for reconnaissance at sea during war, as well as for measuring sea depths.

Prerequisite propagation of sound waves – the presence of a material medium. In a vacuum, sound waves do not propagate, since there are no particles there that transmit the interaction from the source of vibration.

Therefore, due to the lack of atmosphere, complete silence reigns on the Moon. Even the fall of a meteorite on its surface is not audible to the observer.

In each medium, sound travels at different speeds.

Speed of sound in air- approximately 340 m/s.

Speed of sound in water- 1500 m/s.

Speed of sound in metals, steel- 5000 m/s.

In warm air, the speed of sound is greater than in cold air, which leads to a change in the direction of sound propagation.

FORK

- This U-shaped metal plate, the ends of which can vibrate after being struck.

Published tuning fork the sound is very weak and can only be heard at a short distance.
Resonator- a wooden box on which a tuning fork can be attached serves to amplify the sound.
In this case, sound emission occurs not only from the tuning fork, but also from the surface of the resonator.
However, the duration of the sound of a tuning fork on a resonator will be shorter than without it.

E X O

Loud noise, reflected from obstacles, returns to the source of sound a few moments later, and we hear echo.

By multiplying the speed of sound by the time elapsed from its origin to its return, you can determine twice the distance from the sound source to the obstacle.
This method of determining the distance to objects is used in echolocation.

Some animals, for example the bats,
also use the phenomenon of sound reflection using the echolocation method

Echolocation is based on the property of sound reflection.

Sound - running mechanical wave on and transfers energy.
However, the power of simultaneous conversation of all people on the globe is hardly more than the power of one Moskvich car!

Ultrasound.

· Vibrations with frequencies exceeding 20,000 Hz are called ultrasound. Ultrasound is widely used in science and technology.

· The liquid boils when an ultrasonic wave passes through (cavitation). In this case, water hammer occurs. Ultrasounds can tear pieces off the surface of metal and crush solids. Ultrasound can be used to mix immiscible liquids. This is how emulsions in oil are prepared. Under the influence of ultrasound, saponification of fats occurs. Washing devices are designed on this principle.

· Widely used ultrasound in hydroacoustics. Ultrasounds of high frequency are absorbed very weakly by water and can spread over tens of kilometers. If they meet the bottom, iceberg or other solid, they are reflected and give an echo of great power. An ultrasonic echo sounder is designed on this principle.

In metal ultrasound spreads practically without absorption. Using the ultrasonic location method, it is possible to detect the smallest defects inside a part of large thickness.

· The crushing effect of ultrasound is used for the manufacture of ultrasonic soldering irons.

Ultrasonic waves, sent from the ship, are reflected from the sunken object. The computer detects the time the echo appears and determines the location of the object.

· Ultrasound is used in medicine and biology for echolocation, for identifying and treating tumors and some defects in body tissues, in surgery and traumatology for cutting soft and bone tissues during various operations, for welding broken bones, for destroying cells (high power ultrasound).

Infrasound and its impact on humans.

Vibrations with frequencies below 16 Hz are called infrasound.

In nature, infrasound occurs due to the vortex movement of air in the atmosphere or as a result of slow vibrations different bodies. Infrasound is characterized by weak absorption. Therefore, it spreads over long distances. The human body reacts painfully to infrasonic vibrations. Under external influences caused by mechanical vibration or sound waves at frequencies of 4-8 Hz, a person feels movement internal organs, at a frequency of 12 Hz - an attack of seasickness.

· Highest intensity infrasonic vibrations create machines and mechanisms that have surfaces large sizes, performing low-frequency mechanical vibrations (infrasound of mechanical origin) or turbulent flows of gases and liquids (infrasound of aerodynamic or hydrodynamic origin).

Let's move on to considering sound phenomena.

The world of sounds around 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, airplanes and other objects.

Pay attention!

The sources of sound are vibrating bodies.

Example:

Let's secure an elastic metal ruler in a vice. If its free part, the length of which is selected in a certain way, is set into oscillatory motion, then the ruler will make a sound (Fig. 1).

Thus, the oscillating ruler is the source of sound.

Let's consider the image of a sounding string, the ends of which are fixed (Fig. 2). The blurred outline of this string and the apparent thickening in the middle indicate that the string is vibrating.

If you bring the end of a paper strip closer to the sounding string, the strip will bounce from the shocks of the string. While 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 hold it with a bow), the tuning fork will sound (Fig. 4).

Let us bring a light ball (glass bead) suspended on a thread to the sounding tuning fork - the ball will bounce off the tuning fork, indicating vibrations of its branches (Fig. 5).

To “record” the oscillations of a tuning fork with a low (about \(16\) Hz) natural frequency and a large amplitude of oscillations, you can screw a thin and narrow metal strip with a point at the end to the end of one of its branches. The tip must be bent down and lightly touch the 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 point is very close to a sinusoid. Thus, we can assume that each branch of a sounding tuning fork performs harmonic oscillations.

Various experiments indicate that any sound source necessarily vibrates, even if these vibrations are invisible to the eye. For example, the sounds of the voices of people and many animals arise as a result of vibrations of their vocal cords, the sound of wind instruments musical instruments, the sound of a siren, the whistle of the wind, the rustling of leaves, the rumble of thunder are caused by fluctuations in air masses.

Pay attention!

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 its free end is lengthened so much that its vibration frequency becomes less than \(16\) Hz.

The human ear is capable of perceiving as sound mechanical vibrations with a frequency ranging from \(16\) to \(20000\) 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 arbitrary, as they depend on the age of people and individual characteristics their hearing aid. Typically, 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 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 sound waves. They are emitted and used for their “negotiations” by dolphins, bats and some other living creatures.

A sound wave (sound vibrations) is a mechanical vibration of 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 upward in a vice and thereby lengthen the free end so that its vibration frequency becomes less than 20 Hz. Research has shown that the human ear is capable of perceiving as sound mechanical vibrations of bodies occurring at a frequency from 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 the individual characteristics of their hearing aid. Typically, 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 higher than 20,000 Hz. Vibrations with frequencies 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 hum of engines, the rustling of leaves and the howling of the wind, the singing of birds and the voices of people. People began to guess about how sounds are born and what they are 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 encyclopedist Aristotle, based on observations, correctly explained the nature of sound, believing that a sounding body creates alternating compression and rarefaction of air. Thus, a vibrating string either compresses or rarefies the air, and thanks to the elasticity of the air, these alternating effects are transmitted further into space - from layer to layer, elastic waves arise. When they reach our ear, they impact the eardrums and cause the sensation of sound. By ear, a person perceives elastic waves with a frequency ranging from approximately 16 Hz to 20 kHz (1 Hz - 1 vibration per second). In accordance with this, elastic waves in any medium, the frequencies of which lie within the specified limits, are called sound waves or simply sound. In air at a temperature of 0° C and normal pressure sound travels 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 - fan, compressor, turbine, combustion chamber, etc., but also of the noise of the jet stream, vortex, turbulent air flows that occur when flowing around the aircraft at high speeds. A body rushing rapidly through the air or water seems to break the flow flowing around it and periodically generates regions of rarefaction and compression in the medium. As a result, sound waves are generated. Sound can travel in the form of longitudinal and transverse waves. In gaseous and liquid media, only longitudinal waves arise when the oscillatory motion of particles occurs only in the direction in which the wave propagates. In solid bodies, in addition to longitudinal ones, there also arise transverse waves when the particles of the medium oscillate in directions perpendicular to the direction of propagation of the wave. There, striking the string perpendicular to its direction, we force a wave to run along the string. The human ear is not equally sensitive 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 sensation of pressing pain in the ears. The intensity of sound waves at which this occurs is called the pain threshold. The concepts of tone and timbre of sound are also important in the study of sound. Any real sound, be it a human voice or the playing of a musical instrument, is not a simple harmonic vibration, but a peculiar mixture of many harmonic vibrations with a certain set of frequencies. The one that has the lowest frequency is called the fundamental tone, the others are called overtones. Various quantities The overtones inherent in a particular sound give it a special coloring - timbre. The difference between one timbre and another is determined not only by the number, but also by the intensity of the overtones accompanying the sound of the fundamental tone. By timbre, we easily distinguish the sounds of a violin and a piano, a guitar and a flute, and recognize the voices of familiar people.

Oscillation frequency called the number of complete oscillations per second. The unit of frequency measurement is 1 hertz (Hz). 1 hertz corresponds to one complete (in one direction or the other) oscillation, occurring in one second.
Period is the time (s) during which one complete oscillation occurs. The higher the frequency of oscillations, 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 the ear perceives sound vibrations in the range of 16-20,000 Hz.
Amplitude vibration is the greatest deviation of an oscillating body from its original (quiet) position. The greater the amplitude of the vibration, the louder the sound. The sounds of human speech are complex sound vibrations, consisting of one or another number of simple vibrations, varying in frequency and amplitude. Each speech sound has its own unique combination of vibrations of different frequencies and amplitudes. Therefore, the shape of vibrations of one speech sound is noticeably different from the shape of another, which shows graphs of vibrations during the pronunciation of the sounds a, o and y.

A person characterizes any sounds in accordance with his perception by volume level and pitch.

The world is filled with a wide variety of sounds: the ticking of clocks and the hum of engines, the rustling of leaves and the howling of the wind, the singing of birds and the voices of people. People began to guess about how sounds are born and what they are a very long time ago. Even the ancient Greek philosopher and encyclopedist Aristotle, based on observations, correctly explained the nature of sound, believing that a sounding body creates alternating compression and rarefaction of air. Last year the author worked on the problem of the nature of sound and completed research work: “In the World of Sounds,” in which the sound frequencies of a musical scale were calculated using a glass of water.

Sound is characterized by quantities: frequency, wavelength and speed. It is also characterized by amplitude and volume. Therefore, we live in a diverse world of sounds and its variety of shades.

At the end of my previous research, I had a fundamental question: are there ways to determine the speed of sound at home? Therefore, we can formulate the problem: we need to find ways or a way to determine the speed of sound.

Theoretical foundations of the doctrine of sound

World of sounds

Do-re-mi-fa-sol-la-si

Gamma of sounds. Do they exist independently of the ear? Are these only subjective sensations, and then the world itself is silent, or is it a reflection of real reality in our consciousness? If the latter, then even without us the world will ring with a symphony of sounds.

Legend also attributes to Pythagoras (582-500 BC) the discovery of numerical relations corresponding to different musical sounds. Passing by a forge where several workers were forging iron, Pythagoras noticed that sounds were in the ratio of fifth, fourth and octave. Entering the forge, he became convinced that the hammer that gave the octave, compared with the heaviest hammer, had a weight equal to 1/2 of the latter, the hammer that gave the fifth had a weight equal to 2/3, and the quart had a weight equal to 3/4 of the heavy hammer. Upon returning home, Pythagoras hung strings with weights proportional to 1/2: 2/3: 3/4 at the ends and allegedly found that the strings, when struck, produced the same musical intervals. Physically, the legend does not stand up to criticism, the anvil, when struck by different hammers, produces its own one and the same tone, and the laws of string vibration do not confirm the legend. But, in any case, the legend speaks of the ancient teachings of harmony. The merits of the Pythagoreans in the field of music are undoubted. They came up with the fruitful idea of measuring the tone of a sounding string by measuring its length. They knew the “monochord” device - a box made of cedar planks with one stretched string on the lid. When you strike a string, it produces one specific tone. If you divide the string into two sections, supporting it with a triangular peg in the middle, it will produce a higher tone. It sounds so similar to the main tone that when sounded simultaneously they almost merge into one tone. The relationship of two tones in music is an interval. When the string length ratio is 1/2:1, the interval is called an octave. The fifth and fourth intervals known to Pythagoras are obtained if the peg of the monochord is moved so that it separates 2/3 or 3/4 of the strings, respectively.

As for the number seven, it is associated with some even more ancient and mysterious idea of people of a semi-religious, semi-mystical nature. Most likely, however, this is due to astronomical division lunar month for four seven-day weeks. This number has appeared for thousands of years in various legends. So, we find it in an ancient papyrus, which was written by the Egyptian Ahmes 2000 BC. This curious document is entitled: “Instructions for acquiring the knowledge of all secret things.” Among other things, we find there a mysterious problem called “stairs”. It talks about a ladder of numbers representing powers of the number seven: 7, 49, 343, 2401, 16,807. Under each number is a hieroglyph picture: cat, mouse, barley, measure. Papyrus does not provide a clue to this problem. Modern interpreters of the Ahmes papyrus decipher the condition of the problem as follows: Seven persons have seven cats, each cat eats seven mice, each mouse can eat seven ears of barley, each ear can grow seven measures of grain. How much grain will cats save? Why not a problem with production content, proposed 40 centuries ago?

The modern European musical scale has seven tones, but not at all times and not all peoples had a seven-tone scale. So, for example, in ancient China A scale of five tones was used. For purposes of tuning uniformity, the pitch of this reference tone must be strictly declared by international agreement. Since 1938, a tone corresponding to a frequency of 440 Hz (440 vibrations per second) has been adopted as such a fundamental tone. Several tones sounding simultaneously form a musical chord. People with so-called absolute pitch can hear individual tones in a chord.

You, of course, know mostly the structure of the human ear. Let us recall it briefly. The ear consists of three parts: 1) the outer ear, ending with the eardrum; 2) the middle ear, which, with the help of three auditory ossicles: the malleus, the incus and the stapes, transmits vibrations of the eardrum to the inner ear; 3) the inner ear, or labyrinth, consists of the semicircular canals and the cochlea. The cochlea is a sound-receiving apparatus. Inner ear filled with liquid (lymph), set into oscillatory motion by blows of the stirrup on the membrane, tightening the oval window in the bony capsule of the labyrinth. On the septum dividing the cochlea into two parts, along its entire length, the finest nerve fibers of gradually increasing length are located in transverse rows.

The world of sounds is real! But, of course, one should not think that this world evokes exactly the same sensations in everyone. Asking whether other people perceive sounds in exactly the same way as you does is not a scientific way of asking the question.

1. 2. Sound sources. Sound vibrations

What all sounds have in common is that the bodies that generate them, i.e., the sources of sound, vibrate.

An elastic metal ruler fixed in a vice will make a sound if its free part, the length of which is selected in a certain way, is brought into oscillatory motion. IN in this case The vibrations of the sound source are obvious.

Research has shown that the human ear is capable of perceiving as sound mechanical vibrations of bodies occurring with a frequency from 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 the individual characteristics of their hearing aid. Typically, 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 higher than 20,000 Hz.

Vibrations with frequencies 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 hum of engines, the rustling of leaves and the howling of the wind, the singing of birds and the voices of people. People began to guess about how sounds are born and what they are 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 encyclopedist Aristotle, based on observations, correctly explained the nature of sound, believing that a sounding body creates alternating compression and rarefaction of air. Thus, a vibrating string either compresses or rarefies the air, and thanks to the elasticity of the air, these alternating effects are transmitted further into space - from layer to layer, elastic waves arise. When they reach our ear, they impact the eardrums and cause the sensation of sound.

By hearing, a person perceives elastic waves with a frequency ranging from approximately 16 Hz to 20 kHz (1 Hz - 1 vibration per second). In accordance with this, elastic waves in any medium, the frequencies of which lie within the specified limits, are called sound waves or simply sound. In air at a temperature of 0° C and normal pressure, sound travels at a speed of 330 m/s.

The concepts of tone and timbre of sound are also important in the study of sound. Any real sound, be it a human voice or the playing of a musical instrument, is not a simple harmonic vibration, but a peculiar mixture of many harmonic vibrations with a certain set of frequencies. The one with the lowest frequency is called the fundamental tone, the others - overtones. The different number of overtones inherent in a particular sound gives it a special coloring - timbre. The difference between one timbre and another is determined not only by the number, but also by the intensity of the overtones accompanying the sound of the fundamental tone. By timbre, we easily distinguish the sounds of a violin and a piano, a guitar and a flute, and recognize the voices of familiar people.

1. 4. Pitch and timbre of sound

Let's make two different strings sound on a guitar or balalaika. We will hear different sounds: one is lower, the other is higher. The sounds of a man's voice are lower than the sounds of a woman's voice, the sounds of a bass are lower than those of a tenor, and the sounds of a soprano are higher than an alto.

What does the pitch of sound depend on?

We can conclude that the pitch of the sound depends on the frequency of vibration: the higher the frequency of vibration of the sound source, the higher the sound it produces.

A pure tone is the sound of a source oscillating at one frequency.

Sounds from other sources (for example, the sounds of various musical instruments, people's voices, the sound of a siren and many others) are a collection of vibrations different frequencies, i.e. a set of pure tones.

The lowest (i.e. smallest) frequency of such a complex sound is called the fundamental frequency, and the corresponding sound of a certain pitch is called the fundamental tone (sometimes simply called the tone). The pitch of a complex sound is determined precisely by the pitch of its fundamental tone.

All other tones of a complex sound are called overtones. Overtones determine the timbre of a sound, that is, its quality that allows us to distinguish the sounds of some sources from the sounds of others. For example, we easily distinguish the sound of a piano from the sound of a violin, even if these sounds have the same pitch, that is, the same fundamental frequency. The difference between these sounds is due to a different set of overtones.

Thus, the pitch of a sound is determined by the frequency of its fundamental tone: the higher the frequency of the fundamental tone, the higher the sound.

The timbre of a sound is determined by the totality of its overtones.

1. 5. Why are there different sounds?

Sounds differ from each other in volume, pitch and timbre. The loudness of the sound depends partly on the distance of the listener's ear from the sounding object, and partly on the amplitude of the vibration of the latter. The word amplitude means the distance that a body travels from one extreme point to another during its oscillations. The greater this distance, the louder the sound.

The pitch of a sound depends on the speed or frequency of vibration of the body. The more vibrations an object makes in one second, the higher the sound it produces.

However, two sounds that are exactly the same in volume and pitch may differ from each other. The musicality of a sound depends on the number and strength of overtones present in it. If a violin string is made to vibrate along its entire length so that no additional vibrations occur, then the lowest tone that it is capable of producing will be heard. This tone is called the main tone. However, if additional fluctuations occur on it individual parts, then additional higher notes will appear. In harmony with the main tone, they will create a special, violin sound. These higher notes compared to the main tone are called overtones. They determine the timbre of a particular sound.

1. 6. Reflection and propagation of disturbances.

A disturbance of part of a stretched rubber tube or spring moves along its length. When a disturbance reaches the end of the tube, it is reflected regardless of whether the end of the tube is fixed or free. The held end is sharply pulled upward and then brought to its original position. The ridge formed on the tube moves along the tube to the wall, where it is reflected. In this case, the reflected wave has the shape of a depression, i.e., it is located below the average position of the tube, while the original antinode was above. What is the reason for this difference? Imagine the end of a rubber tube fixed in the wall. Because it is fixed, it cannot move. The upward force of the incoming impulse tends to force it to move upward. However, since it cannot move, there must be an equal and opposite downward force emanating from the support and applied to the end of the rubber tube, and therefore the reflected impulse is located with the antinode down. The phase difference between the reflected and original pulses is 180°.

1. 7. Standing waves

When the hand holding the cutting tube moves up and down and the frequency of the movement gradually increases, a point is reached at which a single antinode is obtained. A further increase in the frequency of arm vibration will lead to the formation of a double antinode. If you measure the frequency of hand movements, you will see that their frequency has doubled. Since it is difficult to move your hand more quickly, it is better to use a mechanical vibrator.

The waves produced are called standing or stationary waves. They are formed because the reflected wave is superimposed on the incident one.

IN this study There are two waves: incident and reflected. They have the same frequency, amplitude and wavelength, but travel in opposite directions. These are traveling waves, but they interfere with each other and thus create standing waves. This has the following consequences: a) all particles in each half wavelength oscillate in phase, that is, they all move in the same direction at the same time; b) each particle has an amplitude different from the amplitude of the next particle; c) the phase difference between the vibrations of particles of one half-wave and the vibrations of particles of the next half-wave is 180°. This simply means that they either deviate as far as possible in opposite directions at the same time, or if they find themselves in the middle position, they begin to move in opposite directions.

Some particles do not move (they have zero amplitude) because the forces acting on them are always equal and opposite. These points are called nodal points or nodes, and the distance between two subsequent nodes is half the wavelength, i.e. 1\2 λ.

The maximum movement occurs at points and the amplitude of these points is twice the amplitude of the incident wave. These points are called antinodes, and the distance between two subsequent antinodes is half the wavelength. The distance between the node and the next antinode is one-quarter of the wavelength, i.e. 1\4λ.

A standing wave is different from a traveling wave. In a traveling wave: a) all particles have the same oscillation amplitude; b) each particle is not in phase with the next.

1. 8. Resonance tube.

The resonant pipe is a narrow pipe in which vibrations of the air column are created. To change the length of the air column, use different ways, for example changes in water level in a pipe. The closed end of the pipe is a knot because the air in contact with it is stationary. The open end of the pipe is always an antinode, since the amplitude of vibrations is maximum here. There is one node and one antinode. The length of the tube is approximately one-fourth the length of the standing wave.

In order to show that the length of the air column is inversely proportional to the frequency of the wave, it is necessary to use a series of tuning forks. It is better to use a small loudspeaker connected to a calibrated oscillator audio frequency, instead of fixed-frequency tuning forks. Instead of water pipes, a long pipe with a piston is used, since this makes it easier to select the length of the air columns. A constant sound source is placed near the end of the pipe, and the resonant lengths of the air column are obtained for frequencies of 300 Hz, 350 Hz, 400 Hz, 450 Hz, 500 Hz, 550 Hz and 600 Hz.

When water is poured into a bottle, a certain tone of sound is produced as the air in the bottle begins to vibrate. The pitch of this tone increases as the volume of air in the bottle decreases. Each bottle has a certain natural frequency, and when you blow over the open neck of the bottle, a sound can also be produced.

At the beginning of the war of 1939-1945. the searchlights were focused on aircraft using equipment that operated in the audio range. To prevent them from focusing, some crews threw empty bottles out of the planes when they were caught in the spotlight. Loud sounds of falling bottles were perceived by the receiver, and the spotlights lost focus

1. 9. Wind musical instruments.

The sounds produced by wind instruments depend on the standing waves that arise in the pipes. The tone depends on the length of the pipe and the type of air vibration in the pipe.

For example, an open organ pipe. Air is blown into the pipe through the hole and hits a sharp protrusion. This causes the air in the pipe to vibrate. Since both ends of the pipe are open, there is always an antinode at each end. The simplest type of oscillation is one where there is an antinode at each end and one node in the middle. These are fundamental vibrations, and the length of the tube is approximately half the wavelength. Fundamental frequency =c/2l, where c is the speed of sound and l is the length of the pipe.

A closed organ pipe has a stopper at the end, meaning the end of the pipe is closed. This means that there is always a node at this end. It is quite obvious that: a) the fundamental frequency of a closed pipe is half the fundamental frequency of an open pipe of the same length; b) only odd overtones can be formed with a closed pipe. Thus, the tonal range of an open pipe is greater than that of a closed pipe.

Physical conditions change the sound of musical instruments. An increase in temperature causes an increase in the speed of sound in air and, therefore, an increase in the fundamental frequency. The length of the pipe also increases slightly, causing a decrease in frequency. When playing an organ, for example in a church, performers ask that the heat be turned on so that the organ can sound at its normal temperature. Stringed instruments have string tension controls. An increase in temperature leads to some expansion of the string and a decrease in tension.

Chapter 2. Practical part

2. 1. Method for determining the speed of sound using a resonant tube.

The device is shown in the figure. The resonant pipe is a long narrow pipe A connected to reservoir B through a rubber pipe. There is water in both pipes. When B is raised, the length of the air column in A decreases, and when B is lowered, the length of the air column in A increases. Place an oscillating tuning fork on top of A when the length of the air column at A is practically zero. You won't hear any sound. As the length of the air column in A increases, you will hear the sound intensify, reach a maximum, and then begin to fade. Repeat this procedure, adjusting B so that the length of the air column in A produces maximum sound. Then measure the length l1 of the air column.

A loud sound is heard because the natural frequency of a column of air of length l1 is equal to the natural frequency of the tuning fork, and therefore the air column vibrates in unison with it. You have found the first resonance position. In fact, the length of the oscillating air is somewhat greater than the air column in A.

If you omit. At even lower levels, so that the length of the air column increases, you will find another position in which the sound reaches maximum strength. Determine this position precisely and measure the length l2 of the air column. This is the second resonance position. As before, the apex is at the open end of the pipe and the node is at the surface of the water. This can only be achieved in the case shown in the figure, in which case the length of the air column in the pipe is approximately 3\4 wavelengths (3\4 λ).

Subtracting the two measurements gives:

3\4 λ - 1\4 λ = l2 - l1, therefore, 1\2 λ = l2 - l1.

So, c = ν λ = ν 2 (l2 - l1), where ν is the frequency of the tuning fork. This is a fast and fairly accurate way to determine the speed of sound in air.

2. 2. Experiment and calculations.

To determine the speed of the sound wave, we used following tools and equipment:

Universal tripod;

Thick-walled glass tube, sealed at one end, 1.2 meters long;

Tuning fork, frequency 440 Hz, note “A”;

Hammer;

Water bottle;

Yardstick.

Progress of the study:

1. Assembled a tripod on which I attached the rings to the coupling.

2. Placed the glass tube on a tripod.

3. By adding water to the tube and exciting sound waves on a tuning fork, he created standing waves in the tube.

4. Experimentally, I achieved such a height of the water column that the sound waves in the glass tube were amplified so that resonance was observed in the tube.

5. Measured the first length of the end of the tube free from water - l2 = 58 cm = 0.58 m

6. Added water to the tube again. (Repeat steps 3, 4, 5) – l1 = 19 cm = 0.19 m

7. Performed calculations using the formula: c = ν λ = ν 2 (l2 - l1),

8. s = 440 Hz * 2 (0.58 m - 0.19 m) = 880 * 0.39 = 343.2 m\s

The result of the study is the speed of sound = 343.2 m/s.

2. 3. Conclusions of the practical part

Using the selected equipment, determine the speed of sound in air. We compared the result obtained with the table value – 330 m/s. The resulting value is approximately equal to the tabulated value. The discrepancies were due to measurement errors, the second reason: the table value is given at a temperature of 00C, and in the apartment the air temperature = 240C.

Therefore, the proposed method for determining the speed of sound using a resonant tube can be applied.

Conclusion.

The ability to calculate and determine the characteristics of sound is very useful. As follows from the study, the characteristics of sound: volume, amplitude, frequency, wavelength - these values are inherent in certain sounds, from them we can determine what sound we hear in this moment. We are again faced with a mathematical pattern of sound. But although the speed of sound can be calculated, it depends on the temperature of the room and the space where the sound occurs.

Thus, the purpose of the study was fulfilled.

The research hypothesis was confirmed, but in the future it is necessary to take into account measurement errors.

Based on this, the research objectives were completed:

Studied theoretical basis this question;

Patterns have been identified;

The necessary measurements have been completed;

Calculations of the speed of sound have been performed;

The obtained calculation results were compared with existing tabular data;

An assessment of the results obtained is given.

As a result of the work: o Learned to determine the speed of sound using a resonant tube; o I encountered the problem of different speeds of sound at different temperatures, so I will try to investigate this issue in the near future.

Sound sources. Sound vibrations

Sound – these are mechanical elastic waves propagating in gases, liquids, and solids.

Reason for the sound - vibration (oscillations) of bodies, although these vibrations are often invisible to our eyes.

Sound sources - physical bodies that vibrate, i.e. tremble or vibrate at a frequency
from 16 to 20,000 times per second. The vibrating body can be solid, for example, a string
or the earth's crust, gaseous, for example, a stream of air in wind musical instruments
or liquid, for example, waves on water.

Volume

10 dB – whisper;

20–30 dB – noise standards in residential premises;
50 dB– medium volume conversation;
80 d B – the noise of a running truck engine;
130 dB– pain threshold

Sound louder than 180 dB can even cause eardrum rupture.

High sounds represented by high-frequency waves - for example, birdsong.

Low sounds These are low-frequency waves, such as the sound of a large truck engine.

Sound waves

Sound waves- These are elastic waves that cause a person to feel the sensation of sound.

The property of water - it conducts sound well - is widely used for reconnaissance at sea during war, as well as for measuring sea depths.

A necessary condition for the propagation of sound waves is the presence of a material medium. In a vacuum, sound waves do not propagate, since there are no particles there that transmit the interaction from the source of vibration.

Therefore, due to the lack of atmosphere, complete silence reigns on the Moon. Even the fall of a meteorite on its surface is not audible to the observer.

In each medium, sound travels at different speeds.

Speed of sound in air- approximately 340 m/s.

Speed of sound in water- 1500 m/s.

Speed of sound in metals, steel- 5000 m/s.

In warm air, the speed of sound is greater than in cold air, which leads to a change in the direction of sound propagation.

FORK

- This U-shaped metal plate, the ends of which can vibrate after being struck.

E X O

A loud sound, reflected from obstacles, returns to the source of sound after a few moments, and we hear echo.

Some animals, such as bats,
also use the phenomenon of sound reflection using the echolocation method

Echolocation is based on the property of sound reflection.

Sound - running mechanical wave on and transfers energy.
However, the power of simultaneous conversation of all people on the globe is hardly more than the power of one Moskvich car!

Ultrasound.

· Vibrations with frequencies exceeding 20,000 Hz are called ultrasound. Ultrasound is widely used in science and technology.

· Widely used ultrasound in hydroacoustics. Ultrasounds of high frequency are absorbed very weakly by water and can spread over tens of kilometers. If they encounter the bottom, iceberg or other solid body in their path, they are reflected and produce an echo of great power. An ultrasonic echo sounder is designed on this principle.

In metal ultrasound spreads practically without absorption. Using the ultrasonic location method, it is possible to detect the smallest defects inside a part of large thickness.

· The crushing effect of ultrasound is used for the manufacture of ultrasonic soldering irons.

Ultrasonic waves, sent from the ship, are reflected from the sunken object. The computer detects the time the echo appears and determines the location of the object.

Infrasound and its impact on humans.

Vibrations with frequencies below 16 Hz are called infrasound.

In nature, infrasound occurs due to the vortex movement of air in the atmosphere or as a result of slow vibrations of various bodies. Infrasound is characterized by weak absorption. Therefore, it spreads over long distances. The human body reacts painfully to infrasonic vibrations. Under external influences caused by mechanical vibration or sound waves at frequencies of 4-8 Hz, a person feels the movement of internal organs, and at a frequency of 12 Hz - an attack of seasickness.

· Highest intensity infrasonic vibrations create machines and mechanisms that have large surfaces that perform low-frequency mechanical vibrations (infrasound of mechanical origin) or turbulent flows of gases and liquids (infrasound of aerodynamic or hydrodynamic origin).