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

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

Sounds are transmitted through the air

You've probably seen how the guitar is played. Perhaps you can do this yourself. Another important thing is the sound the strings make in a guitar when you pluck them. That's right. But if you could place a guitar in a vacuum and pluck the strings, you would be very surprised that the guitar would not make any sound.

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

Sources of sound - oscillating 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. Sources of sound are bodies that vibrate. These vibrations are transmitted by air molecules and our ear, perceiving these vibrations, interprets them into sensations of sound that we understand.

It's not difficult to check. Take a glass or crystal goblet and place 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.

Now let several people wrap their hands around the glass as completely as possible, along with the stem, trying not to leave a single free area, except for a very small place for hitting with a spoon. Hit the glass again. You will hardly hear any sound, and the one that will be will be weak and very short. What does this mean?

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 hardly vibrated, and therefore made almost no sound.

The same goes for all other experiments you can think of and conduct. 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 different living creatures generally vary greatly.

With the help of this video lesson you can study the topic “Sound Sources. Sound vibrations. Pitch, timbre, volume." In this lesson you will learn what sound is. We will also consider the ranges of sound vibrations perceived by human hearing. Let's determine what can be the source of sound and what conditions are necessary for its occurrence. We will also study such sound characteristics as pitch, timbre and volume.

The topic of the lesson is devoted to sound sources and sound vibrations. We will also talk about the characteristics of sound - pitch, volume and timbre. Before talking about sound, about sound waves, let's remember that mechanical waves propagate in elastic media. The part of longitudinal mechanical waves that is perceived by the human hearing organs is called sound, sound waves. Sound is the mechanical waves perceived by the human hearing organs that cause sound sensations .

Experiments show that the human ear and human hearing organs perceive vibrations with frequencies from 16 Hz to 20,000 Hz. It is this range that we call sound. Of course, there are waves whose frequency is less than 16 Hz (infrasound) and more than 20,000 Hz (ultrasound). But this range, these sections are not perceived by the human ear.

Rice. 1. Hearing range of the human ear

As we said, the areas of infrasound and ultrasound are not perceived by the human hearing organs. Although they can be perceived, for example, by some animals and insects.

What's happened ? Sound sources can be any body that vibrates at a sound frequency (from 16 to 20,000 Hz)

Rice. 2. An oscillating ruler clamped in a vice can be a source of sound.

Let's turn to experience and see how a sound wave is formed. To do this we need a metal ruler, which we will clamp in a vice. Now, when we act on the ruler, we will be able to observe vibrations, but we will not hear any sound. And yet a mechanical wave is created around the ruler. Please note that when the ruler is moved to one side, an air seal is formed here. In the other direction there is also a seal. Air vacuum forms between these seals. Longitudinal wave - this is a sound wave consisting of compactions and rarefaction of air. The oscillation frequency of the ruler in this case is less than the sound frequency, so we do not hear this wave, this sound. Based on the experience we have just observed, at the end of the 18th century, a device called a tuning fork was created.

Rice. 3. Propagation of longitudinal sound waves from a tuning fork

As we have seen, sound appears as a result of vibrations of a body with a sound frequency. Sound waves propagate in all directions. There must be a medium between the human hearing aid and the source of sound waves. This medium can be gaseous, liquid, or solid, but it must be particles capable of transmitting vibrations. The process of transmitting sound waves must necessarily occur where there is matter. If there is no substance, we will not hear any sound.

For sound to exist you need:

1. Sound source

2. Wednesday

3. Hearing aid

4. Frequency 16-20000Hz

5. Intensity

Now let's move on to discussing sound characteristics. The first is the pitch of the sound. Sound height - characteristic that is determined by the frequency of oscillations. The higher the frequency of the body that produces vibrations, the higher the sound will be. Let's look again at the ruler held in a vice. As we have already said, we saw vibrations, but did not hear any sound. If we now make the length of the ruler shorter, we will hear the sound, but it will be much more difficult to see the vibrations. Look at the line. If we act on it now, we will not hear any sound, but we will observe vibrations. If we shorten the ruler, we will hear a sound of a certain pitch. We can make the length of the ruler even shorter, then we will hear a sound of even higher pitch (frequency). We can observe the same thing with tuning forks. If we take a large tuning fork (also called a demonstration fork) and hit the legs of such a tuning fork, we can observe the vibration, but we will not hear the sound. If we take another tuning fork, then when we hit it we will hear a certain sound. And the next tuning fork, a real tuning fork, which is used to tune musical instruments. It makes a sound corresponding to the note A, or, as they also say, 440 Hz.

The next characteristic is the timbre of the sound. Timbre called sound color. How can this characteristic be illustrated? Timbre is the difference between two identical sounds performed by different musical instruments. You all know that we only have seven notes. If we hear the same note A played on a violin and on a piano, we can tell them apart. We can immediately tell which instrument created this sound. It is this feature - the color of the sound - that characterizes the timbre. It must be said that timbre depends on what sound vibrations are reproduced, in addition to the fundamental tone. The fact is that arbitrary sound vibrations are quite complex. They consist of a set of individual vibrations, they say vibration spectrum. It is the reproduction of additional vibrations (overtones) that characterizes the beauty of the sound of a particular voice or instrument. Timbre is one of the main and brightest manifestations of sound.

Another characteristic is volume. The volume of sound depends on the amplitude of vibrations. Let's take a look and make sure that loudness is related to the amplitude of vibrations. So, let's take a tuning fork. Let's do the following: if you hit the tuning fork weakly, the amplitude of vibrations will be small and the sound will be quiet. If you now hit the tuning fork harder, the sound will be much louder. This is due to the fact that the amplitude of the oscillations will be much greater. The perception of sound is a subjective thing, it depends on what kind of hearing aid is used and how a person feels.

List of additional literature:

Is the sound so familiar to you? // Quantum. - 1992. - No. 8. - P. 40-41. Kikoin A.K. About musical sounds and their sources // Quantum. - 1985. - No. 9. - P. 26-28. Elementary physics textbook. Ed. G.S. Landsberg. T. 3. - M., 1974.

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 in the air or in water seems to break the flow flowing around it, periodically generating 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 solids, in addition to longitudinal waves, transverse waves also arise when particles of the medium vibrate 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. 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.

• 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.

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

Sounds are transmitted through the air

You've probably seen how the guitar is played. Perhaps you can do this yourself. Another important thing is the sound the strings make in a guitar when you pluck them. That's right. But if you could place a guitar in a vacuum and pluck the strings, you would be very surprised that the guitar would not make any sound.

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

Sources of sound - oscillating 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. Sources of sound are bodies that vibrate. These vibrations are transmitted by air molecules and our ear, perceiving these vibrations, interprets them into sensations of sound that we understand.

It's not difficult to check. Take a glass or crystal goblet and place 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 knock again. The sound will change and become much shorter.

Now let several people wrap their hands around the glass as completely as possible, along with the stem, trying not to leave a single free area, except for a very small place for hitting with a spoon. Hit the glass again. You will hardly hear any sound, and the one that will be will be weak and very short. What does this mean?

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 hardly vibrated, and therefore made almost no sound.

The same goes for all other experiments you can think of and conduct. 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 different living creatures generally vary greatly.

The ears are a very thin and delicate instrument given to us by nature, so we should take care of it, since there is no replacement or analogue in the human body.

Sound is sound waves that cause vibrations of tiny particles of air, other gases, and liquid and solid media. Sound can only arise where there is a substance, no matter what state of aggregation it is in. In vacuum conditions, where there is no medium, sound does not propagate, because there are no particles that act as distributors of sound waves. For example, in space. Sound can be modified, altered, turning into other forms of energy. Thus, sound converted into radio waves or electrical energy can be transmitted over distances and recorded on information media.

Sound wave

The movements of objects and bodies almost always cause fluctuations in the environment. It doesn't matter if it's water or air. During this process, the particles of the medium to which the vibrations of the body are transmitted also begin to vibrate. Sound waves arise. Moreover, movements are carried out in forward and backward directions, progressively replacing each other. Therefore, the sound wave is longitudinal. There is never any lateral movement up and down in it.

Characteristics of sound waves

Like any physical phenomenon, they have their own quantities, with the help of which properties can be described. The main characteristics of a sound wave are its frequency and amplitude. The first value shows how many waves are formed per second. The second determines the strength of the wave. Low-frequency sounds have low frequency values, and vice versa. The frequency of sound is measured in Hertz, and if it exceeds 20,000 Hz, then ultrasound occurs. There are plenty of examples of low-frequency and high-frequency sounds in nature and the world around us. The chirping of a nightingale, the rumble of thunder, the roar of a mountain river and others are all different sound frequencies. The amplitude of the wave directly depends on how loud the sound is. The volume, in turn, decreases with distance from the sound source. Accordingly, the further the wave is from the epicenter, the smaller the amplitude. In other words, the amplitude of a sound wave decreases with distance from the sound source.

Sound speed

This indicator of a sound wave is directly dependent on the nature of the medium in which it propagates. Both humidity and air temperature play a significant role here. In average weather conditions, the speed of sound is approximately 340 meters per second. In physics, there is such a thing as supersonic speed, which is always greater than the speed of sound. This is the speed at which sound waves travel when an aircraft moves. The plane moves at supersonic speed and even outruns the sound waves it creates. Due to the pressure gradually increasing behind the aircraft, a shock wave of sound is formed. The unit of measurement for this speed is interesting and few people know it. It's called Mach. Mach 1 is equal to the speed of sound. If a wave travels at Mach 2, then it travels twice as fast as the speed of sound.

Noises

There is constant noise in human daily life. The noise level is measured in decibels. The movement of cars, the wind, the rustling of leaves, the interweaving of people's voices and other sound noises are our daily companions. But the human auditory analyzer has the ability to get used to such noise. However, there are also phenomena that even the adaptive abilities of the human ear cannot cope with. For example, noise exceeding 120 dB can cause pain. The loudest animal is the blue whale. When it makes sounds, it can be heard over 800 kilometers away.

Echo

How does an echo occur? Everything is very simple here. A sound wave has the ability to be reflected from different surfaces: from water, from a rock, from walls in an empty room. This wave returns to us, so we hear secondary sound. It is not as clear as the original one, since some of the energy of the sound wave is dissipated when traveling to the obstacle.

Echolocation

Sound reflection is used for various practical purposes. For example, echolocation. It is based on the fact that with the help of ultrasonic waves it is possible to determine the distance to the object from which these waves are reflected. Calculations are made by measuring the time it takes for ultrasound to travel to a location and return. Many animals have the ability to echolocation. For example, bats and dolphins use it to search for food. Echolocation has found another application in medicine. During ultrasound examinations, a picture of a person’s internal organs is formed. The basis of this method is that ultrasound, entering a medium other than air, returns back, thus forming an image.

Sound waves in music

Why do musical instruments make certain sounds? Guitar strumming, piano strumming, low tones of drums and trumpets, the charming thin voice of a flute. All these and many other sounds arise due to air vibrations or, in other words, due to the appearance of sound waves. But why is the sound of musical instruments so diverse? It turns out that this depends on several factors. The first is the shape of the tool, the second is the material from which it is made.

Let's look at this using string instruments as an example. They become a source of sound when the strings are touched. As a result, they begin to vibrate and send different sounds into the environment. The low sound of any stringed instrument is due to the greater thickness and length of the string, as well as the weakness of its tension. And vice versa, the more tightly the string is stretched, the thinner and shorter it is, the higher the sound obtained as a result of playing.

Microphone action

It is based on the conversion of sound wave energy into electrical energy. In this case, the strength of the current and the nature of the sound are directly dependent. Inside any microphone there is a thin plate made of metal. When exposed to sound, it begins to perform oscillatory movements. The spiral to which the plate is connected also vibrates, resulting in an electric current. Why does he appear? This is because the microphone also has built-in magnets. When the spiral oscillates between its poles, an electric current is generated, which goes along the spiral and then to a sound column (loudspeaker) or to equipment for recording on an information medium (cassette, disk, computer). By the way, the microphone in the phone has a similar structure. But how do microphones on landlines and mobile phones work? The initial phase is the same for them - the sound of the human voice transmits its vibrations to the microphone plate, then everything follows the scenario described above: a spiral, which, when moving, closes two poles, a current is created. What's next? With a landline telephone, everything is more or less clear - just like in a microphone, the sound, converted into electric current, runs through the wires. But what about a cell phone or, for example, a walkie-talkie? In these cases, the sound is converted into radio wave energy and hits the satellite. That's all.

Resonance phenomenon

Sometimes conditions are created when the amplitude of vibrations of the physical body increases sharply. This occurs due to the convergence of the values ​​of the frequency of forced oscillations and the natural frequency of oscillations of the object (body). Resonance can be both beneficial and harmful. For example, to get a car out of a hole, it is started and pushed back and forth in order to cause resonance and give the car inertia. But there have also been cases of negative consequences of resonance. For example, in St. Petersburg, about a hundred years ago, a bridge collapsed under soldiers marching in unison.