Summary: Sources of sound. Sound vibrations

Sound sources. Sound vibrations

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

Sound - These are mechanical elastic waves propagating in gases, liquids, solids.

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

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

Volume

The loudness depends on the amplitude of the 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 – norm of noise in residential premises;
50 dB– medium volume conversation;
80 d B - the noise of a running truck engine;
130 dB- threshold pain sensation

Sound above 180 dB can even cause a rupture of the eardrum.

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

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

sound waves

sound waves These are elastic waves that cause the sensation of sound in a person.

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

Putting your ear to the rails, you can hear the noise 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 how the stones knock against each other, how the pebbles rustle during the surf.

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

Necessary condition propagation of sound waves - the presence of a material environment. in a vacuum sound waves do not propagate, since there are no particles transmitting interaction from the source of vibrations.

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

Sound travels at different speeds in every medium.

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

Sound speed in water- 1500 m/s.

The speed of sound in metals, in 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 oscillate after hitting it.

Published tuning fork The sound is very weak and can only be heard at a short distance.
Resonator - 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 the tuning fork on the resonator will be less than without it.

E X O

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

Multiplying the speed of sound by the time elapsed from its occurrence to its return, you can determine twice the distance from the sound source to the barrier.
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, applying the method of echolocation

Echolocation is based on the property of sound reflection.

Sound - running mechanical ox on the and transfers energy.
However, the power of the simultaneous conversation of all people on the globe 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.

Liquid boils when passing through an ultrasonic wave (cavitation). This creates a hydraulic shock. Ultrasounds can tear off pieces from the metal surface and crush solids. Immiscible liquids can be mixed with ultrasound. This is how oil emulsions are prepared. Under the action of ultrasound, saponification of fats occurs. Washing machines are based on this principle.

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

in metal ultrasound spreads almost without absorption. Using the method of ultrasonic location, it is possible to detect the smallest defects inside a part of a 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 of the appearance of the echo and determines the location of the object.

· Ultrasound is used in medicine and biology for echolocation, for the detection and treatment of tumors and some defects in body tissues, in surgery and traumatology for dissection of soft and bone tissues during various operations, for welding broken bones, for cell destruction (high power ultrasound).

Infrasound and its effect on humans.

Oscillations 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 painfully reacts to infrasonic vibrations. Under external influences caused mechanical vibration or a sound wave at frequencies of 4-8 Hz, a person feels movement internal organs, at a frequency of 12 Hz - an attack of seasickness.

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

Questions.

1. Tell us about the experiments depicted in figures 70-73. What conclusion follows from them?

In the first experiment (Fig. 70), a metal ruler clamped in a vise makes a sound when it vibrates.
In the second experiment (Fig. 71), one can observe the vibrations of the string, which also makes a sound.
In the third experiment (Fig. 72) the sound of a tuning fork is observed.
In the fourth experiment (Fig. 73), the vibrations of the tuning fork are "recorded" on a sooty plate. All these experiments demonstrate the oscillatory nature of the origin of sound. Sound comes from vibrations. In the fourth experiment, this can also be visually observed. The tip of the needle leaves a trace in the form close to a sinusoid. In this case, the sound does not appear from nowhere, but is generated by sound sources: a ruler, a string, a tuning fork.

2. How common property possess all sound sources?

Any source of sound is bound to oscillate.

3. Mechanical vibrations of what frequencies are called sound and why?

Sound vibrations are called mechanical vibrations with frequencies from 16 Hz to 20,000 Hz, because. in this frequency range they are perceived by a person.

4. What vibrations are called ultrasonic? infrasonic?

Oscillations with frequencies above 20,000 Hz are called ultrasonic, and those with frequencies below 16 Hz are called infrasonic.

5. Tell us about measuring the depth of the sea using echolocation.

Exercises.

1. We hear the sound of the flapping wings of a flying mosquito. but a flying bird does not. Why?

The oscillation frequency of the wings of a mosquito is 600 Hz (600 strokes per second), a sparrow is 13 Hz, and the human ear perceives sounds from 16 Hz.

Sound sources. Sound vibrations

Man lives in the world of sounds. Sound for a person is a source of information. He warns people of 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 capture helps to survive.

Sound - These are mechanical elastic waves propagating in gases, liquids, solids.

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

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

Volume

The loudness depends on the amplitude of the 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 – norm of noise in residential premises;
50 dB– medium volume conversation;
80 d B - the noise of a running truck engine;
130 dB- pain threshold

Sound above 180 dB can even cause a rupture of the eardrum.

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

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

sound waves

sound waves These are elastic waves that cause the sensation of sound in a person.

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

Putting your ear to the rails, you can hear the noise 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 how the stones knock against each other, how the pebbles rustle during the surf.

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

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

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

Sound travels at different speeds in every medium.

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

Sound speed in water- 1500 m/s.

The speed of sound in metals, in 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 oscillate after hitting it.

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 fixed, 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 the tuning fork on the resonator will be less than without it.

E X O

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

Multiplying the speed of sound by the time elapsed from its occurrence to its return, you can determine twice the distance from the sound source to the barrier.
This method of determining the distance to objects is used in echolocation.

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

Echolocation is based on the property of sound reflection.

Sound - running mechanical ox on the and transfers energy.
However, the power of the 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.

Liquid boils when passing through an ultrasonic wave (cavitation). This creates a hydraulic shock. Ultrasounds can tear off pieces from the metal surface and crush solids. Immiscible liquids can be mixed with ultrasound. This is how oil emulsions are prepared. Under the action of ultrasound, saponification of fats occurs. Washing machines are based on this principle.

· Widely used ultrasound in hydroacoustics. Ultrasounds of high frequency are absorbed by water very weakly and can propagate for tens of kilometers. If they encounter a bottom, iceberg or other solid body on their way, they are reflected and give an echo of great power. An ultrasonic echo sounder is based on this principle.

in metal ultrasound spreads almost without absorption. Using the method of ultrasonic location, it is possible to detect the smallest defects inside a part of a 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 of the appearance of the echo and determines the location of the object.

· Ultrasound is used in medicine and biology for echolocation, for the detection and treatment of tumors and some defects in body tissues, in surgery and traumatology for dissection of soft and bone tissues during various operations, for welding broken bones, for cell destruction (high power ultrasound).

Infrasound and its effect on humans.

Oscillations 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 painfully reacts to infrasonic vibrations. With external influences caused by mechanical vibration or a sound wave at frequencies of 4-8 Hz, a person feels the movement of internal organs, at a frequency of 12 Hz - an attack of seasickness.

The greatest intensity infrasonic vibrations they 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).

Before you understand what sound sources are, think about what sound is? We know that light is radiation. Reflected from objects, this radiation enters our eyes, and we can see it. Taste and smell are small particles of the body that are perceived by our respective receptors. What kind of sound is this animal?

Sounds are transmitted through the air

You must have seen how the guitar is played. Perhaps you yourself know how to do it. It is important that the strings make a different sound in the guitar when they are pulled. All right. But if you could put the guitar in a vacuum and pull the strings, then you would be very surprised that the guitar would not make any sound.

Such experiments were carried out with a variety of bodies, and the result was always the same - no sound was heard in airless space. From this follows a logical conclusion sound is transmitted through the air. Therefore, sound is something that happens to particles of air substances and sound-producing bodies.

Sound sources - vibrating bodies

Further. As a result of a wide variety of numerous experiments, it was possible to establish that sound arises due to the vibration of bodies. Sound sources are bodies that vibrate. These vibrations are transmitted by air molecules and our ear, perceiving these vibrations, interprets them into sound sensations that are understandable to us.

It is not difficult to check this. Take a glass or crystal goblet and put it on the table. Tap it lightly with a metal spoon. You will hear a long thin sound. Now touch the glass with your hand and tap again. The sound will change and become much shorter.

And now let several people wrap their arms around the glass as completely as possible, along with the leg, trying not to leave a single free area, except for the very small place to hit with a spoon. Hit the glass again. You will hardly hear any sound, and the one that will be will turn out to be weak and very short. What does it say?

In the first case, after the impact, the glass oscillated freely, its vibrations were transmitted through the air and reached our ears. In the second case, most of the vibrations were absorbed by our hand, and the sound became much shorter, as the vibrations of the body decreased. In the third case, almost all vibrations of the body were instantly absorbed by the hands of all participants and the body almost did not oscillate, and consequently, almost no sound was emitted.

The same goes for all other experiments you can think of and run. Vibrations of bodies, transmitted to air molecules, will be perceived by our ears and interpreted by the brain.

Sound vibrations of different frequencies

So sound is vibration. Sound sources transmit sound vibrations through the air to us. Why, then, do we not hear all the vibrations of all objects? Because vibrations come in different frequencies.

The sound perceived by the human ear is sound vibrations with a frequency of approximately 16 Hz to 20 kHz. Children hear sounds of higher frequencies than adults, and the ranges of perception of various living beings generally differ very much.

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. More ancient Greek philosopher and the encyclopedic scientist Aristotle, based on observations, correctly explained the nature of sound, believing that the sounding body creates alternate 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 the musical scale were calculated using a glass of water.

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

At the end of the previous study, I had a fundamental question: are there ways to determine the speed of sound at home? Therefore, we can formulate a 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 reality in our minds? If the latter, then even without us the world will ring with a symphony of sounds.

Even Pythagoras (582-500 BC) is credited with the discovery of numerical relationships corresponding to different musical sounds. Passing by a forge, where several workers were forging iron, Pythagoras noticed that the sounds were in relation to fifths, quarts and octaves. Entering the forge, he made sure that the hammer that gave an octave, compared with the heaviest hammer, had a weight equal to 1/2 of the latter, the hammer that gave a fifth had a weight equal to 2/3, and a quart - 3/4 of a 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, gave the same musical intervals. Physically, the legend does not stand up to criticism, the anvil, when struck by various hammers, emits 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 antiquity of the doctrine of harmony. The merits of the Pythagoreans in the field of music are beyond doubt. They own the fruitful idea of ​​measuring the tone of a sounding string by measuring its length. They knew the device "monochord" - a box of cedar boards with one stretched string on the lid. If you strike a string, it emits one specific tone. If you divide the string into two sections, supporting it with a triangular peg in the middle, then it will emit a higher tone. It sounds so similar to the main tone that when sounded simultaneously, they almost merge into one tone. The ratio of two tones in music is an interval. When the ratio of string lengths is 1/2:1, the interval is called an octave. The fifth and fourth intervals known to Pythagoras are obtained if the monochord peg is moved so that it separates 2/3 or 3/4 strings, respectively.

As for the number seven, it is associated with some even more ancient and mysterious representation of people of a semi-religious, semi-mystical character. Most likely, however, this is due to astronomical fission. lunar month for four seven-day weeks. This number appears for thousands of years in various legends. Yes, we find it in ancient papyrus, which was written by the Egyptian Ahmes in 2000 BC. This curious document is entitled: "Instruction for the Acquisition of Knowledge of All Secret Things." Among other things, we find there a mysterious task called "stairs". It talks about a ladder of numbers representing the powers of the number seven: 7, 49, 343, 2401, 16 807. Under each number is a hieroglyph-picture: cat, mouse, barley, measure. The papyrus provides no 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 can cats save? Why not a task with industrial 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 used a scale of five tones. For the purpose of tuning unity, the pitch of this control tone must be strictly declared by international agreement. Since 1938, a tone corresponding to a frequency of 440 Hz (440 oscillations per second) has been adopted as such a fundamental tone. Several tones sounding simultaneously form a musical chord. People who have the so-called absolute pitch can hear individual tones in a chord.

You, of course, know basically the structure of the human ear. Let us recall it briefly. The ear consists of three parts: 1) the outer ear, ending in the tympanic membrane; 2) the middle ear, which, with the help of three auditory ossicles: the hammer, anvil and stirrup, supplies the vibrations of the tympanic membrane 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. The inner ear is filled with fluid (lymph) oscillating motion by blows of the stirrup on the membrane, tightening the oval window in the bone box of the labyrinth. On the septum dividing the cochlea into two parts, along its entire length, the thinnest 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 for everyone. Asking if other people perceive sounds in exactly the same way as you is an unscientific question.

1. 2. Sound sources. Sound vibrations

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, etc.

Common to all sounds is that the bodies that generate them, that is, the sources of sound, oscillate.

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

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 either compresses or rarefies the air, and due to the elasticity of the air, these alternating effects 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 travels at a speed of 330 m/s.

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 in the air or in water, as it were, breaks the flow around it, periodically generates areas of rarefaction and compression in the medium. The result is sound waves.

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 that has 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.

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 the male voice are lower than the sounds of the woman's voice, the bass sounds are lower than the tenor sounds, the soprano sounds are higher than the alto.

What determines the pitch of a sound?

It can be concluded that the pitch of the sound depends on the frequency of vibrations: the higher the frequency of vibrations of the sound source, the higher the sound it emits.

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

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

The lowest (i.e., the smallest) frequency of such a complex sound is called the fundamental frequency, and the corresponding sound of a certain height is called the fundamental tone (sometimes it is called simply a 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, which allows us to distinguish the sounds of some sources from the sounds of others. For example, we can 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: the greater the frequency of the fundamental, 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 the other during their hesitation. The greater this distance, the louder the sound.

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

However, two sounds that are absolutely identical in volume and pitch may differ from each other. The musicality of a sound depends on the number and strength of the overtones present in it. If the string of a violin is made to oscillate along its entire length so that no additional vibrations occur, then the lowest tone that it can only produce will be heard. This tone is called the main tone. However, if additional vibrations of individual parts occur on it, then additional higher notes will appear. Harmonizing with the main tone, they will create a special, violin sound. These notes, higher than the root, are called overtones. They determine the timbre of a particular sound.

1.6. Reflection and propagation of perturbations.

The perturbation of a part of a stretched rubber tube or spring moves along its length. When the perturbation 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 up 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 below the average position of the tube, while the initial antinode was above. What is the reason for this difference? Imagine the end of a rubber tube fixed in a wall. Since it is fixed, it cannot move. The upwardly directed force of the incoming impulse seeks to make it move upwards. 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 so the reflected pulse is antinode down. The phase difference of the reflected and original pulses is 180°.

1. 7. Standing waves

When the hand holding the rubber tube is moved up and down and the frequency of movement is gradually increased, a point is reached at which a single antinode is obtained. A further increase in the frequency of oscillation of the hand 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 the hand more quickly, it is better to use a mechanical vibrator.

The generated waves are called standing or stationary waves. They form because the reflected wave is superimposed on the incident wave.

In this study, there are two waves: incident and reflected. They have the same frequency, amplitude and wavelength, but propagate 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 of the wavelength oscillate in phase, i.e. 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 oscillations of the particles of one half-wave and the oscillations of the particles of the next half-wave is 180°. This simply means that they are either deflected as much as possible in opposite directions at the same time, or, if they are 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 or nodes, and the distance between two subsequent nodes is half the wavelength, i.e. 1\2 λ.

The maximum motion 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 fourth 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 tube is a narrow tube in which a column of air vibrates. To change the length of the air column, apply different ways, such as changes in the 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 oscillation amplitude is maximum here. There is one node and one antinode. The length of the tube is approximately one fourth of the standing wave length.

In order to show that the length of the air column is inversely proportional to the frequency of the wave, a series of tuning forks must be used. It is better to use a small loudspeaker connected to a calibrated generator audio frequency, instead of fixed frequency tuning forks. Instead of pipes with water, a long pipe with a piston is used, since this makes it easier to choose the length of the air columns. A constant sound source is placed near the end of the pipe, and 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 is produced as the air in the bottle begins to vibrate. The pitch of this tone rises as the volume of air in the bottle decreases. Each bottle has a specific frequency of its own, and when you blow over the open neck of the bottle, a sound can also be produced.

At the beginning of the war 1939-1945. searchlights were focused on aircraft using equipment operating in the audio range. To prevent them from focusing, some crews were thrown out of planes empty bottles when they hit the spotlight. The 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 occur in the pipes. The tone depends on the length of the pipe and the type of air vibrations in the pipe.

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

Closed organ pipe has a plug at the end, i.e. 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 closed pipe is half the fundamental frequency open pipe the same length; b) with a closed pipe, only odd overtones can be formed. Thus, the range of tones of an open pipe is greater than that of a closed one.

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 somewhat, causing the frequency to decrease. When playing the organ, for example, in a church, performers ask to turn on the heating so that the organ sounds 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. A method for determining the speed of sound using a resonant tube.

The device is shown in the figure. The resonant tube is a long narrow tube A connected to the reservoir B through a rubber tube. Both pipes contain water. 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 in A is practically zero. You won't hear any sound. As the column of air at A increases in length, you will hear the sound increase in intensity, reach a maximum, and then begin to fade. Repeat this procedure, adjusting B so that the length of the air column in A produces the maximum sound. Then measure the length l1 of the air column.

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

If you drop. Even lower, so that the length of the air column increases, you will find another position in which the sound reaches maximum strength. Determine exactly this position 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, whereby the length of the air column in the pipe is approximately 3/4 wavelength (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 tuning fork frequency. This is a fast and fairly accurate way to determine the speed of sound in air.

2. 2. Experiment and calculations.

The following tools and equipment were used to determine the speed of a sound wave:

Tripod universal;

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

A tuning fork, the frequency of which is 440 Hz, the note "la";

Hammer;

Water bottle;

Yardstick.

Research progress:

1. I assembled a tripod, on which I fixed the rings on the sleeve.

2. Placed the glass tube in a tripod.

3. By pouring water into the tube, and exciting sound waves on the tuning fork, he created standing waves in the tube.

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

5. Measured the first length of the end of the tube free from water - l2 \u003d 58 cm \u003d 0.58 m

6. Added more water to the pipe. (Repeat steps 3, 4, 5) - l1 = 19 cm = 0.19 m

7. Performed calculations according to the formula: c \u003d ν λ \u003d ν 2 (l2 - l1),

8. s \u003d 440 Hz * 2 (0.58 m - 0.19 m) \u003d 880 * 0.39 \u003d 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 equipment of your choice, determine the speed of sound in air. We compared the result with the tabular value - 330 m / s. The resulting value is approximately equal to the table. The discrepancies were due to measurement errors, the second reason: the tabular 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: loudness, amplitude, frequency, wavelength - these values ​​\u200b\u200bare inherent in certain sounds, they can be used to determine what kind of sound we hear in this moment. We are again faced with the mathematical regularity of sound. But the speed of sound, although it is possible to calculate, but it depends on the temperature of the room and the space where the sound occurs.

Thus, the purpose of the study was fulfilled.

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

Based on this, the objectives of the study were fulfilled:

Studied theoretical basis this issue;

Regularities are found out;

The necessary measurements have been taken;

Calculations of the speed of sound are made;

The results of the calculations were compared with the already available tabular data;

An assessment of the obtained results is given.

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