SOUND SPEED
SOUND SPEED
Movements in an elastic medium, provided that the shape of its profile remains unchanged. The speed of a harmonic wave is called. also the phase speed of sound. Usually S. z. is a constant value for a given island with given external conditions. conditions and does not depend on the frequency of the wave and its amplitude. In cases where it turns out to be different for different frequencies, we talk about sound dispersion.
For gases and liquids, where it usually propagates adiabatically (that is, the change in temperature associated with compression and rarefaction in the sound wave does not have time to equalize over the period), S. z. is expressed like this:
с=?(Kad/r)=?(1/badr).
с=?(gp0/r)=?(gRT/m). (f-la Laplace),
where g=Cp/Cv is the ratio of heat capacities at constant pressure and volume, p0 is the average in the medium, R is the universal. , m - mol. gas S. z. in gases less than in liquids, and in liquids less, as a rule, than in solids. bodies, therefore, when gas is liquefied S. z. increases. Below are the values of S. z. (m/s) for certain gases and liquids, and in those cases where there is a dispersion of the sound wave, its values are given for low frequencies, when the period of the sound wave is greater than the relaxation.
SPEED OF SOUND IN GASES AT 0°C AND PRESSURE 1 ATM
Nitrogen.........……... 334
Oxygen........... 316
Air............ … 331
Helium......... 965
Hydrogen......... 1284
Methane............... ... 430
Ammonia.............. 415
S. z. in gases it increases with increasing temperature and pressure (at room temperature, the relative change in the solar value in air is approximately 0.17% with a change in temperature of 1°C). In liquids, the solar value, as a rule, decreases by several degrees with increasing temperature. m/s by 1°C;
SPEED OF SOUND IN LIQUIDS AT 20°C
Water........………………..... 1490
Benzene..........………………. 1324
Ethanol.....…………. 1180
Mercury...........…………………. 1453
Glycerin....………………..... 1923
The exception to this rule is water, in the cut S. z. increases with increasing temperature and reaches a maximum at a temperature of 74°C, and decreases with a further increase in temperature. With increasing pressure S. z. in water increases by approximately 0.01% per 1 atm. In sea water N. z. increases with increasing temperature, salinity and depth, which determines the course of sound. rays in the sea, in particular the existence of an underwater sound channel.
S. z. in mixtures of gases or liquids depends on the concentration of the components of the mixture.
S. z. in isotropic TVs. bodies is determined by the elastic modulus of the body and its density. In unlimited TV. longitudinal and shear (transverse) waves propagate in the environment, and the phase S. z. for a longitudinal wave is equal to:
and for shear:
where E is Young's modulus, G is shear modulus, v is coefficient. Poisson, K - volumetric compression modulus. The speed of propagation of longitudinal waves is always greater than the speed of shear waves (see table). On TV limited bodies sizes there are other types of waves, for example. , the speed of which is less than cl and ct. In plates, rods and other solids. waveguides propagate, the speed of which is determined not only by the characteristics of the substance, but also by the geo. body parameters. S. z. for a longitudinal wave in a thin rod is equal to сl st = ?(E/r). In monocryst. TV bodies S. z. depends on the direction of propagation of the wave relative to the crystallographic. axes. In many villages of S. z. depends on the presence of foreign impurities. In metals and alloys S. z. significantly depends on the processing they were subjected to (rolling, forging, annealing, etc.). In piezoelectrics and ferroelectrics S. z. is determined not only by the elastic moduli, but also by the piezoelectric moduli, and may also depend on the electrical tension. fields.
SPEED OF SOUND IN SOME SOLIDS
In ferromagnets, S. z. depends on the magnetic tension. fields.
Measurement of S. z. used to determine many properties of the world, such as the compressibility of gases and liquids, solids, Debye temperature, etc. Measurement of small changes in solar energy. yavl. feels. method for determining the presence of impurities in gases and liquids. On TV bodies of measurement S. z. and its dependence on various factors make it possible to study the band structure of semiconductors, the structure of Fermi surfaces in metals, etc. A number of control and measurements. applications of ultrasound in basic engineering. on measurements of the S. z.
Physical encyclopedic dictionary. - M.: Soviet Encyclopedia. Editor-in-Chief A. M. Prokhorov. 1983 .
SOUND SPEED
Velocity of propagation of an elastic wave in a medium. s in axis direction X, sound pressure R can be represented in the form p = p(x - - ct), Where t- time. For plane harmony, waves in a medium without dispersion and SZ. expressed in terms of frequency w and k Floy c= w/k. With speed With spreads harmoniously waves, called also phase S. z. In media in which the shape of an arbitrary wave changes during propagation, harmonic. the waves nevertheless retain their shape, but the phase velocity turns out to be different for different frequencies, the dispersion of sound. In these cases, the concept is also used group speed. At large amplitudes of the elastic wave, nonlinear effects appear (see. Nonlinear acoustics), leading to a change in any waves, including harmonic ones: the speed of propagation of each point of the wave profile depends on the pressure at this point, increasing with increasing pressure, which leads to distortion of the wave shape.
Speed of sound in gases and liquids. In gases and liquids, sound propagates in the form of volumetric compression-discharge waves. If the propagation process occurs adiabatically (which, as a rule, is the case), i.e. e. the change in temperature in the sound wave does not have time to level out even after 1 / 2 ,
period, heat from heated (compressed) areas does not have time to move to cold (rarefied) areas, then S. z. equal to 
, Where R - pressure in a substance is its density, and the index s shows that the derivative is taken at constant entropy. This S. z. called adiabatic. Expression for S.
Where TO hell - adiabatic. modulus of all-round compression of matter, - adiabatic. compressibility, 
- isothermal compressibility = - the ratio of heat capacities at constant pressure and volume.
In an ideal gas, where R = = 8.31 J/mol*K is the universal gas constant, T - abs. -molecular mass of the gas. This is the so-called l a p l a s o v a S. z. In a gas, it coincides in order of magnitude with the average thermal speed of motion of molecules. The value is called the new S. z., it determines the S. z. at isothermal propagation process, which can take place at very low frequencies. In most cases, S. z. corresponds to the Laplace value.
S. z. in gases less than in liquids, and in liquids, as a rule, less, In ideal gases at a given temperature S. z. does not depend on pressure and increases with increasing temperature as . Change of S. z. equals 
, where and are small increments of speed and temperature compared to their values With And T. At room temperature it relates. change in S. z. in air is approximately 0.17% per 1 K. In liquids, the solar value, as a rule, decreases with increasing temperature and its change is, for example, for acetone -5.5 m/s*K, for ethyl alcohol -3 .6 m/s * K. An exception to this rule is water, in the cut. h. at room temperature it increases with increasing temperature by 2.5 m/s*K, Table 1- Speed of sound in some gases at °C*
Oxygen | |||
Carbon dioxide | |||
Hydrogen iodide | |||
* Speed values are given for normal pressure.
Table 2- Speed of sound in some liquids at 20 °C
Ethanol | |||
Carbon tetrachloride | |||
Glycerol | |||
In sea water N. z. depends on temperature, salinity and depth. These dependencies are complex. To calculate S. z. in the sea, tables calculated according to empirical data are used. Since temperature, pressure, and sometimes salinity change with depth, the northwestern in the ocean is a function of depth c(z). This dependence significantly determines the nature of sound propagation in the ocean (see. Hydroacoustics). In particular, it determines the existence underwater sound channel, the position of the axis and other characteristics depend on the time of year, time of day and on geography and location.
In liquefied gases S. z. increases at the same temperature: for example, in gaseous gas at a temperature of -195 ° C it is equal to 176 m/s, in liquid nitrogen at the same temperature 859 m/s, in gaseous and liquid helium at -269 ° With respectively 102 m/s and 198 m/s.
S. z. in mixtures of gases or liquids depends on the concentration of the components. , in which a mixture is taken as a mixture, determined by the molecular weights of the components, taking into account their concentration. In liquid mixtures, the dependence of S. z. from the concentration of components has a rather complex nature, which is associated with the type of intermolecular interactions. Thus, in alcohol-water and acid-water mixtures at a certain concentration there is a maximum S. measurement of S. z. can be used to determine and control the concentration of components of mixtures and solutions.
In liquid helium S. z. increases with decreasing temperature. During a phase transition to a superfluid state, a kink appears in the dependence curve C. h. from the temperature.
In polyatomic gases and almost all liquids there is a dispersion C. z., and in liquids it manifests itself at high ultrasonic and hypersonic frequencies.
In rubbers, polymers and caoutchoucs S. z. depends on the chem. composition and packing density of macromolecules and increases with increasing frequency; in materials of this type with lower density and S. z. less, eg. in silicone rubber C. Speed of sound in solids. Longitudinal and shear (transverse) elastic waves propagate in an unbounded solid medium. In an isotropic solid, the phase velocity for a longitudinal wave is
for shear wave 
Where E - Young's modulus, G- shear modulus, - coefficient Poisson, TO - volumetric compression modulus. The speed of propagation of longitudinal waves is always greater than the speed of shear waves, and the relation is usually satisfied. Values with l And c t for certain isotropic solids are given in table. 3.
Table 3 -Speed of sound in some isotropic solids
In monocrystals S. z. depends on the direction of wave propagation in the crystal (see Crystal acoustics). In those directions in which propagation of purely longitudinal and purely transverse waves is possible, in general there is one value with l and two meanings c t . If the values c t are different, then the corresponding waves are sometimes called. fast and slow transverse waves. In the general case, for each direction of wave propagation in a crystal, there can be three mixed waves with different propagation speeds, which are determined by the corresponding combinations of elastic moduli and oscillation vectors. In plural substances S. z. depends on the presence of foreign impurities. In semiconductors and dielectrics S. z. sensitive to the concentration of impurities; Thus, when a semiconductor is doped with an impurity that increases the number of current carriers, S. z. decreases with increasing concentration; with increasing temperature S. z. increases slightly.
In metals and alloys S. z. depends significantly on previous mechanical and heat treatment: rolling, forging, annealing, etc. This phenomenon is partly associated with dislocations, the presence of which also affects the SZ.
Table 4 - Speed of sound in some single crystals
In metals, as a rule, S. z. decreases with increasing temperature. When the metal transitions to the superconducting state, the nature of the dependence is different: the quantity ds/dT at the transition point changes sign. In strong magnetic fields, certain effects appear depending on the S. z. from mag. fields, which reflect the peculiarities of the behavior of electrons in a single crystal of a metal. Thus, when sound propagates in certain directions, SZs appear in the crystal. kakf-tion mag. fields. Measuring the dependence of S. z. from mag. fields are sensitive. In piezoelectrics And ferroelectrics presence of electromechanical A similar phenomenon is observed in magnetostrictive materials, where the presence of a magnetoelastic connection leads, in addition, to the appearance of a noticeable dependence of the SZ. from magnetic tension field due to the m-effect, E from the magnitude of the magnetic field. fields N. ChangesC. h. with growth N can reach several. percent (sometimes up to tens of percent). The same dependence of S. z. from electrical tension field is observed in ferroelectrics. When acting on static mohanich. In bounded solids, in addition to longitudinal and transverse waves, there are other types of waves. Thus, along the free surface of a solid body or along its boundary with another medium, they propagate surface acoustic waves, the speed of which is less than the speed of body waves characteristic of a given material. For plates, rods and other solid acoustic materials. waveguides are characteristic normal waves, the speed of which is determined not only by the properties of the substance, but also by the geometry of the body. So, for example, S. z. for a longitudinal wave in a rod with an articulation, the transverse dimensions of which are much smaller than the wavelength of sound, different from the S. z. in an unrestricted environment with l(Table 3): 
Measurement methods C. Diffraction of light by ultrasound). Naib. accuracy relative. measurements of the order of 10 -5% (for example, when studying the dependence With temperature or magnetic fields or the concentration of impurities or defects).
Measurements of S. z. are used to define plurals. properties of matter, such as molecular acoustics). Determination of small changes in S. z. is sensitive. method of fixing impurities in gases and liquids. In solids, the measurement is C. Lit.: Landau L. D., L i f sh i c E. M., Theory of Elasticity, 4th ed., M., 1987; them, Hydrodynamics, 4th ed., M., 1988; Bergman L., Ultrasounds and their application in science and technology, trans. from German, 2nd ed., M., 1957; MikhailovI. G., Solovyov V. A., Syrnikov Yu. P., Fundamentals of molecular acoustics, M., 1964; Tables for calculating the speed of sound in sea water, L., 1965; Physical acoustics, ed. W. Mason, trans. from English, vol. 1, part A, M., 1966, ch. 4;t. 4, part B, M., 1970, ch. 7; Kolesnikov A.E., Ultrasonic measurements, 2nd ed., M., 1982; T r u e l l R., E l b a u m Ch., Ch i k B., Ultrasonic methods in solid state physics, trans. from English, M., 1972; Acoustic, A. L. Polyakova.
Physical encyclopedia. In 5 volumes. - M.: Soviet Encyclopedia. Great Soviet Encyclopedia
The speed of propagation of sound waves in a medium. In gases, the speed of sound is less than in liquids, and in liquids it is less than in solids (and for shear waves the speed is always less than for longitudinal ones). speed of sound in gases and vapors from... ... Big Encyclopedic Dictionary
sound speed- speed of propagation of acoustic waves 1. Speed of propagation of an elastic wave in a medium. Unit m/s 2. Phase or group velocity of an acoustic wave in a non-dispersive material for a given direction of propagation. )
