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The trajectory of sound propagation in water. School encyclopedia

We know that sound travels through the air. That's why we can hear. No sounds can exist in a vacuum. But if sound is transmitted through the air, due to the interaction of its particles, will it not also be transmitted by other substances? Will.

Propagation and speed of sound in different media

Sound is not transmitted only by air. Probably everyone knows that if you put your ear to the wall, you can hear conversations in the next room. In this case, the sound is transmitted by the wall. Sounds travel in water and other media. Moreover, sound propagation occurs differently in different environments. The speed of sound varies depending on the substance.

It is curious that the speed of sound in water is almost four times higher than in air. That is, fish hear “faster” than we do. In metals and glass, sound travels even faster. This is because sound is a vibration of a medium, and sound waves travel faster in better conductive media.

The density and conductivity of water is greater than that of air, but less than that of metal. Accordingly, sound is transmitted differently. When moving from one medium to another, the speed of sound changes.

The length of a sound wave also changes as it passes from one medium to another. Only its frequency remains the same. But this is precisely why we can discern who exactly is speaking even through walls.

Since sound is vibrations, all laws and formulas for vibrations and waves are well applicable to sound vibrations. When calculating the speed of sound in air, it should also be taken into account that this speed depends on the air temperature. As temperature increases, the speed of sound propagation increases. Under normal conditions, the speed of sound in air is 340,344 m/s.

Sound waves

Sound waves, as is known from physics, propagate in elastic media. This is why sounds are well transmitted by the earth. By placing your ear to the ground, you can hear the sound of footsteps, clattering hooves, and so on from afar.

As a child, everyone probably had fun putting their ear to the rails. The sound of train wheels is transmitted along the rails for several kilometers. To create the reverse sound absorption effect, soft and porous materials are used.

For example, in order to protect a room from extraneous sounds, or, conversely, to prevent sounds from escaping from the room to the outside, the room is treated and soundproofed. The walls, floor and ceiling are covered with special materials based on foamed polymers. In such upholstery all sounds fade away very quickly.

Where does sound travel faster: in air or in water??? and got the best answer

Answer from Ptishon[guru]
Speed of soundSpeed of sound in gases (0° C; 101325 Pa), m/s Nitrogen 334 Ammonia 415 Acetylene 327 Hydrogen 1284 Air 331.46 Helium 965 Oxygen 316 Methane 430 Carbon monoxide 338 Carbon dioxide 259 Chlorine 206 Speed of sound - speed of propagation of sound waves in the environment. In gases, the speed of sound is less than in liquids. In liquids, the speed of sound is less than in solids. In air, under normal conditions, the speed of sound is 331.46 m/s (1193 km/h). In water, the speed of sound is 1485 m /s. In solids, the speed of sound is 2000-6000 m/s.

Reply from White Rabbit[guru]
In water. In air, the speed of sound at 25 ° C is about 330 m/s in water about 1500 m/s The exact value depends on temperature, pressure, salinity (for water) and humidity (for air)

Reply from BaNkS777[expert]
in the water....

Reply from AnDi[guru]
Do you want to create a sound bomb? Nuclear physicists are in a frenzy F)))

Reply from Vladimir T[guru]
in water, where the density is greater there and faster (molecules are closer and transmission is faster)

Reply from Polina Lykova[active]
Probably in the air (I don’t know for sure). Since all movements are slowed down in water, the sound does not travel so quickly! Well, check it out! Clap your hands underwater. It will be done slower than in the air. My experience =) =8 =(=*8 =P

Reply from 3 answers[guru]

Hello! Here is a selection of topics with answers to your question: Where does sound travel faster: in air or in water???

Over long distances, sound energy travels only along gentle rays that do not touch the ocean floor along the entire path. In this case, the limitation imposed by the environment on the range of sound propagation is its absorption in sea water. The main mechanism of absorption is associated with relaxation processes accompanying the disturbance by an acoustic wave of the thermodynamic equilibrium between the ions and molecules of salts dissolved in water. It should be noted that the main role in absorption in a wide range of sound frequencies belongs to the magnesium sulfur salt MgSO4, although in percentage terms its content in sea water is very small - almost 10 times less than, for example, NaCl rock salt, which nevertheless does not play a role any significant role in sound absorption.

Absorption in sea water, generally speaking, is greater the higher the sound frequency. At frequencies from 3-5 to at least 100 kHz, where the above mechanism dominates, absorption is proportional to frequency to the power of about 3/2. At lower frequencies, a new absorption mechanism is activated (possibly due to the presence of boron salts in water), which becomes especially noticeable in the range of hundreds of hertz; here the level of absorption is anomalously high and falls significantly more slowly with decreasing frequency.

To more clearly imagine the quantitative characteristics of absorption in sea water, we note that due to this effect, sound with a frequency of 100 Hz is attenuated 10 times over a path of 10 thousand km, and with a frequency of 10 kHz - at a distance of only 10 km (Figure 2). Thus, only low-frequency sound waves can be used for long-distance underwater communication, long-range detection of underwater obstacles, etc.

Figure 2 - Distances at which sounds of different frequencies attenuate 10 times when propagating in sea water.

In the region of audible sounds for the frequency range 20-2000 Hz, the propagation range of medium-intensity sounds under water reaches 15-20 km, and in the ultrasound region - 3-5 km.

Based on the sound attenuation values observed in laboratory conditions in small volumes of water, one would expect significantly greater ranges. However, under natural conditions, in addition to attenuation caused by the properties of water itself (the so-called viscous attenuation), its scattering and absorption by various inhomogeneities of the medium also affect it.

Refraction of sound, or curvature of the path of a sound beam, is caused by heterogeneity in the properties of water, mainly vertically, due to three main reasons: changes in hydrostatic pressure with depth, changes in salinity and changes in temperature due to unequal heating of the water mass by the sun's rays. As a result of the combined action of these reasons, the speed of sound propagation, which is about 1450 m/sec for fresh water and about 1500 m/sec for sea water, changes with depth, and the law of change depends on the time of year, time of day, depth of the reservoir and a number of other reasons. . Sound rays emerging from the source at a certain angle to the horizon are bent, and the direction of the bend depends on the distribution of sound speeds in the medium. In summer, when the upper layers are warmer than the lower ones, the rays bend downwards and are mostly reflected from the bottom, losing a significant share of their energy. On the contrary, in winter, when the lower layers of water maintain their temperature, while the upper layers cool, the rays bend upward and undergo multiple reflections from the surface of the water, during which much less energy is lost. Therefore, in winter the range of sound propagation is greater than in summer. Due to refraction, so-called dead zones, i.e. areas located close to the source in which there is no audibility.

The presence of refraction, however, can lead to an increase in the range of sound propagation - the phenomenon of ultra-long-range propagation of sounds under water. At some depth below the surface of the water there is a layer in which sound travels at the lowest speed; Above this depth, the speed of sound increases due to an increase in temperature, and below this depth, due to an increase in hydrostatic pressure with depth. This layer is a kind of underwater sound channel. A beam that has deviated from the channel axis up or down, due to refraction, always tends to fall back into it. If you place the source and receiver of sound in this layer, then even sounds of medium intensity (for example, explosions of small charges of 1-2 kg) can be recorded at distances of hundreds and thousands of km. A significant increase in the range of sound propagation in the presence of an underwater sound channel can be observed when the sound source and receiver are located not necessarily near the channel axis, but, for example, near the surface. In this case, the rays, refracting downward, enter deep-sea layers, where they are deflected upward and exit again to the surface at a distance of several tens of kilometers from the source. Next, the pattern of ray propagation is repeated and as a result a sequence of so-called rays is formed. secondary illuminated zones, which are usually traced to distances of several hundred km.

The propagation of high-frequency sounds, in particular ultrasounds, when the wavelengths are very small, is influenced by small inhomogeneities usually found in natural bodies of water: microorganisms, gas bubbles, etc. These inhomogeneities act in two ways: they absorb and scatter the energy of sound waves. As a result, as the frequency of sound vibrations increases, the range of their propagation decreases. This effect is especially noticeable in the surface layer of water, where there are most inhomogeneities. The scattering of sound by inhomogeneities, as well as uneven surfaces of water and the bottom, causes the phenomenon of underwater reverberation that accompanies the sending of a sound pulse: sound waves, reflecting from a set of inhomogeneities and merging, give rise to a prolongation of the sound pulse, which continues after its end, similar to the reverberation observed in enclosed spaces. Underwater reverberation is a fairly significant interference for a number of practical applications of hydroacoustics, in particular for sonar.

The range of propagation of underwater sounds is also limited by the so-called. the sea's own noises, which have a dual origin. Some of the noise comes from the impact of waves on the surface of the water, from the sea surf, from the noise of rolling pebbles, etc. The other part is related to marine fauna; This includes sounds made by fish and other marine animals.

We perceive sounds at a distance from their sources. Usually sound reaches us through the air. Air is an elastic medium that transmits sound.

If the sound transmission medium is removed between the source and the receiver, the sound will not propagate and, therefore, the receiver will not perceive it. Let's demonstrate this experimentally.

Let's place an alarm clock under the bell of the air pump (Fig. 80). As long as there is air in the bell, the sound of the bell can be heard clearly. As the air is pumped out from under the bell, the sound gradually weakens and finally becomes inaudible. Without a transmission medium, the vibrations of the bell plate cannot travel, and the sound does not reach our ear. Let's let air under the bell and hear the ringing again.

Rice. 80. Experiment proving that sound does not propagate in space where there is no material medium

Elastic substances conduct sounds well, such as metals, wood, liquids, and gases.

Let's put a pocket watch on one end of a wooden board, and move to the other end. Putting your ear to the board, you can hear the clock ticking.

Tie a string to a metal spoon. Place the end of the string to your ear. When you hit the spoon, you will hear a strong sound. We will hear an even stronger sound if we replace the string with wire.

Soft and porous bodies are poor conductors of sound. To protect any room from the penetration of extraneous sounds, the walls, floor and ceiling are laid with layers of sound-absorbing materials. Felt, pressed cork, porous stones, and various synthetic materials (for example, polystyrene foam) made from foamed polymers are used as interlayers. The sound in such layers quickly fades.

Liquids conduct sound well. Fish, for example, are good at hearing footsteps and voices on the shore; this is known to experienced fishermen.

So, sound propagates in any elastic medium - solid, liquid and gaseous, but cannot propagate in space where there is no substance.

The vibrations of the source create an elastic wave of sound frequency in its environment. The wave, reaching the ear, affects the eardrum, causing it to vibrate at a frequency corresponding to the frequency of the sound source. Vibrations of the eardrum are transmitted through the ossicular system to the endings of the auditory nerve, irritate them and thereby cause the sensation of sound.

Let us recall that only longitudinal elastic waves can exist in gases and liquids. Sound in the air, for example, is transmitted by longitudinal waves, i.e., alternating condensations and rarefactions of air coming from the sound source.

A sound wave, like any other mechanical waves, does not propagate in space instantly, but at a certain speed. You can verify this, for example, by watching gunfire from afar. First we see fire and smoke, and then after a while we hear the sound of a shot. The smoke appears at the same time the first sound vibration occurs. By measuring the time interval t between the moment the sound appears (the moment the smoke appears) and the moment it reaches the ear, we can determine the speed of sound propagation:

Measurements show that the speed of sound in air at 0 °C and normal atmospheric pressure is 332 m/s.

The higher the temperature, the higher the speed of sound in gases. For example, at 20 °C the speed of sound in air is 343 m/s, at 60 °C - 366 m/s, at 100 °C - 387 m/s. This is explained by the fact that with increasing temperature, the elasticity of gases increases, and the greater the elastic forces that arise in the medium during its deformation, the greater the mobility of particles and the faster vibrations are transmitted from one point to another.

The speed of sound also depends on the properties of the medium in which sound travels. For example, at 0 °C the speed of sound in hydrogen is 1284 m/s, and in carbon dioxide - 259 m/s, since hydrogen molecules are less massive and less inert.

Nowadays, the speed of sound can be measured in any environment.

Molecules in liquids and solids are closer together and interact more strongly than gas molecules. Therefore, the speed of sound in liquid and solid media is greater than in gaseous media.

Since sound is a wave, to determine the speed of sound, in addition to the formula V = s/t, you can use the formulas you know: V = λ/T and V = vλ. When solving problems, the speed of sound in air is usually considered to be 340 m/s.

Questions

What is the purpose of the experiment depicted in Figure 80? Describe how this experiment is carried out and what conclusion follows from it.
Can sound travel in gases, liquids, and solids? Support your answers with examples.
Which bodies conduct sound better - elastic or porous? Give examples of elastic and porous bodies.
What kind of wave - longitudinal or transverse - is sound propagating in the air? in the water?
Give an example showing that a sound wave does not travel instantly, but at a certain speed.

Exercise 30

Could the sound of a huge explosion on the Moon be heard on Earth? Justify your answer.
If you tie one half of a soap dish to each end of the thread, then using such a telephone you can even talk in a whisper while in different rooms. Explain the phenomenon.
Determine the speed of sound in water if a source oscillating with a period of 0.002 s excites waves in water with a length of 2.9 m.
Determine the wavelength of a sound wave with a frequency of 725 Hz in air, in water and in glass.
One end of a long metal pipe was struck once with a hammer. Will the sound from the impact spread to the second end of the pipe through the metal; through the air inside the pipe? How many blows will a person standing at the other end of the pipe hear?
An observer standing near a straight section of the railway saw steam above the whistle of a locomotive moving in the distance. 2 seconds after the steam appeared, he heard the sound of a whistle, and after 34 seconds the locomotive passed by the observer. Determine the speed of the locomotive.

This lesson covers the topic “Sound Waves”. In this lesson we will continue to study acoustics. First, let's repeat the definition of sound waves, then consider their frequency ranges and get acquainted with the concept of ultrasonic and infrasonic waves. We will also discuss the properties of sound waves in different media and learn what characteristics they have. .

Sound waves – these are mechanical vibrations that, spreading and interacting with the organ of hearing, are perceived by a person (Fig. 1).

Rice. 1. Sound wave

The branch of physics that deals with these waves is called acoustics. The profession of people who are popularly called “hearers” is acousticians. A sound wave is a wave propagating in an elastic medium, it is a longitudinal wave, and when it propagates in an elastic medium, compression and discharge alternate. It is transmitted over time over a distance (Fig. 2).

Rice. 2. Sound wave propagation

Sound waves include vibrations that occur with a frequency from 20 to 20,000 Hz. For these frequencies the corresponding wavelengths are 17 m (for 20 Hz) and 17 mm (for 20,000 Hz). This range will be called audible sound. These wavelengths are given for air, the speed of sound in which is equal to .

There are also ranges that acousticians deal with - infrasonic and ultrasonic. Infrasonic are those that have a frequency of less than 20 Hz. And ultrasonic ones are those that have a frequency greater than 20,000 Hz (Fig. 3).

Rice. 3. Sound wave ranges

Every educated person should be familiar with the frequency range of sound waves and know that if he goes for an ultrasound, the picture on the computer screen will be constructed with a frequency of more than 20,000 Hz.

Ultrasound – These are mechanical waves similar to sound waves, but with a frequency from 20 kHz to a billion hertz.

Waves with a frequency of more than a billion hertz are called hypersound.

Ultrasound is used to detect defects in cast parts. A stream of short ultrasonic signals is directed to the part being examined. In those places where there are no defects, the signals pass through the part without being registered by the receiver.

If there is a crack, an air cavity or other inhomogeneity in the part, then the ultrasonic signal is reflected from it and, returning, enters the receiver. This method is called ultrasonic flaw detection.

Other examples of ultrasound applications are ultrasound machines, ultrasound machines, ultrasound therapy.

Infrasound – mechanical waves similar to sound waves, but having a frequency of less than 20 Hz. They are not perceived by the human ear.

Natural sources of infrasound waves are storms, tsunamis, earthquakes, hurricanes, volcanic eruptions, and thunderstorms.

Infrasound is also an important wave that is used to vibrate the surface (for example, to destroy some large objects). We launch infrasound into the soil - and the soil breaks up. Where is this used? For example, in diamond mines, where they take ore that contains diamond components and crush it into small particles to find these diamond inclusions (Fig. 4).

Rice. 4. Application of infrasound

The speed of sound depends on environmental conditions and temperature (Fig. 5).

Rice. 5. Speed of sound wave propagation in various media

Please note: in air the speed of sound at is equal to , and at , the speed increases by . If you are a researcher, then this knowledge may be useful to you. You may even come up with some kind of temperature sensor that will record temperature differences by changing the speed of sound in the medium. We already know that the denser the medium, the more serious the interaction between particles of the medium, the faster the wave propagates. In the last paragraph we discussed this using the example of dry air and moist air. For water, the speed of sound propagation is . If you create a sound wave (knock on a tuning fork), then the speed of its propagation in water will be 4 times greater than in air. By water, information will reach 4 times faster than by air. And in steel it’s even faster: (Fig. 6).

Rice. 6. Sound wave propagation speed

You know from the epics that Ilya Muromets used (and all the heroes and ordinary Russian people and boys from Gaidar’s RVS) used a very interesting method of detecting an object that is approaching, but is still far away. The sound it makes when moving is not yet audible. Ilya Muromets, with his ear to the ground, can hear her. Why? Because sound is transmitted over solid ground at a higher speed, which means it will reach Ilya Muromets’ ear faster, and he will be able to prepare to meet the enemy.

The most interesting sound waves are musical sounds and noises. What objects can create sound waves? If we take a wave source and an elastic medium, if we make the sound source vibrate harmoniously, then we will have a wonderful sound wave, which will be called musical sound. These sources of sound waves can be, for example, the strings of a guitar or piano. This may be a sound wave that is created in the air gap of a pipe (organ or pipe). From music lessons you know the notes: do, re, mi, fa, sol, la, si. In acoustics, they are called tones (Fig. 7).

Rice. 7. Musical tones

All objects that can produce tones will have features. How are they different? They differ in wavelength and frequency. If these sound waves are not created by harmoniously sounding bodies or are not connected into some kind of common orchestral piece, then such a quantity of sounds will be called noise.

Noise– random oscillations of various physical natures, characterized by the complexity of their temporal and spectral structure. The concept of noise is both domestic and physical, they are very similar, and therefore we introduce it as a separate important object of consideration.

Let's move on to quantitative estimates of sound waves. What are the characteristics of musical sound waves? These characteristics apply exclusively to harmonic sound vibrations. So, sound volume. How is sound volume determined? Let us consider the propagation of a sound wave in time or the oscillations of the source of the sound wave (Fig. 8).

Rice. 8. Sound volume

At the same time, if we did not add a lot of sound to the system (we hit a piano key quietly, for example), then there will be a quiet sound. If we loudly raise our hand high, we cause this sound by hitting the key, we get a loud sound. What does this depend on? A quiet sound has a smaller vibration amplitude than a loud sound.

The next important characteristic of musical sound and any other sound is height. What does the pitch of sound depend on? The height depends on the frequency. We can make the source oscillate frequently, or we can make it oscillate not very quickly (that is, perform fewer oscillations per unit time). Let's consider the time sweep of a high and low sound of the same amplitude (Fig. 9).

Rice. 9. Pitch

An interesting conclusion can be drawn. If a person sings in a bass voice, then his sound source (the vocal cords) vibrates several times slower than that of a person who sings soprano. In the second case, the vocal cords vibrate more often, and therefore more often cause pockets of compression and discharge in the propagation of the wave.

There is another interesting characteristic of sound waves that physicists do not study. This timbre. You know and easily distinguish the same piece of music performed on a balalaika or cello. How are these sounds or this performance different? At the beginning of the experiment, we asked people who produce sounds to make them of approximately the same amplitude, so that the volume of the sound is the same. It’s like in the case of an orchestra: if there is no need to highlight any instrument, everyone plays approximately the same, at the same strength. So the timbre of the balalaika and cello is different. If we were to draw the sound that is produced from one instrument from another using diagrams, they would be the same. But you can easily distinguish these instruments by their sound.

Another example of the importance of timbre. Imagine two singers who graduate from the same music university with the same teachers. They studied equally well, with straight A's. For some reason, one becomes an outstanding performer, while the other is dissatisfied with his career all his life. In fact, this is determined solely by their instrument, which causes vocal vibrations in the environment, i.e. their voices differ in timbre.

References

Sokolovich Yu.A., Bogdanova G.S. Physics: a reference book with examples of problem solving. - 2nd edition repartition. - X.: Vesta: publishing house "Ranok", 2005. - 464 p.
Peryshkin A.V., Gutnik E.M., Physics. 9th grade: textbook for general education. institutions/A.V. Peryshkin, E.M. Gutnik. - 14th ed., stereotype. - M.: Bustard, 2009. - 300 p.