speed of sound


Also found in: Dictionary, Thesaurus, Medical, Legal, Financial, Acronyms, Wikipedia.

speed of sound

[′spēd əv ′sau̇nd]
(acoustics)
The phase velocity of a sound wave. Also known as sonic speed; sonic velocity; sound velocity; velocity of sound.
McGraw-Hill Dictionary of Scientific & Technical Terms, 6E, Copyright © 2003 by The McGraw-Hill Companies, Inc.
The following article is from The Great Soviet Encyclopedia (1979). It might be outdated or ideologically biased.

Speed of Sound

 

the speed of propagation of the phase of a sound wave. It thus represents a phase velocity, in contrast to a group velocity. The speed of sound is usually a constant for a given substance under specified external conditions and usually does not depend on the frequency and amplitude of the wave. When the speed of sound is dependent on the frequency, we speak of the dispersion of sound.

In gases and liquids, sound usually propagates adiabati-cally—that is, the temperature changes associated with compressions and rarefactions in the sound wave do not even out in one period. The speed of sound in this case can be expressed as follows:

Here, Kad is the adiabatic bulk modulus, ρ is the density, βad is the adiabatic compressibility, βis = γβad is the isothermal compressibility, and γ = cp/cv is the ratio of the specific heat at constant pressure cp to the specific heat at constant volume cv.

The speed of sound in an ideal gas is given by Laplace’s formula:

where p0 is the average pressure in the medium, R is the universal gas constant, T is the absolute temperature, and μ is the molecular weight of the gas. Newton’s formula for the speed of sound is obtained when γ = 1; this formula is based on the assumption that the propagation process has an isothermal character. The difference between adiabatic and isothermal processes can usually be ignored in the case of liquids.

Table 1. Speed of sound in gases at 0°C and a pressure of 1 atmosphere
Gasc (m/sec)
Nitrogen.....................................334
Oxygen ..................................316
Air.....................331
Helium ....................965
Hydrogen .............................1,284
Methane..................................430
Ammonia ...................................415

The speed of sound is lower in gases than in liquids and is generally lower in liquids than in solids. For this reason, the speed of sound increases when a gas undergoes liquefaction. Tables 1 and 2 give the values of the speed of sound for some gases and liquids. For cases where acoustic dispersion occurs, the tables give the speed of sound at low frequencies, where the period of the sound wave is longer than the relaxation time.

Table 2. Speed of sound in liquids at 20°C
Liquidc (m/sec)
Water.....................................1,490
Benzene ....................................1,324
Ethyl alcohol ................................1,180
Carbon tetrachloride .......................920
Mercury ....................................1,453
Glycerol ....................................1,923

In gases, the speed of sound increases as the temperature and pressure increase. In liquids, the speed of sound generally decreases as the temperature increases. Water is an exception to this rule. The speed of sound in water increases as the temperature rises to 74°C; with a further increase in temperature, the speed of sound decreases. In seawater, the speed of sound depends on the temperature, salinity, and depth. This dependence determines the paths of sound beams in seawater and is the reason for the existence of underwater sound channels.

In mixtures of gases or liquids, the speed of sound depends on the concentrations of the components of the mixture.

The speed of sound in isotropic solids is determined by the moduli of elasticity and the density of the substance. In an unbounded solid medium, both longitudinal waves and shear (transverse) waves are propagated. In this case, the longitudinal wave has the speed

and the shear wave has the speed

Here, E is Young’s modulus, G is the shear modulus, ν is Pois-son’s ratio, and K is the bulk modulus. The speed of propagation of longitudinal waves is always higher than the speed of shear waves (see Table 3).

The speed of sound in single crystal solids depends on the direction of wave propagation relative to the crystallographic axes. In many substances, the speed of sound depends on the presence of impurities. In metals and alloys, the speed of sound strongly depends on the processing to which the metal has been subjected—for example, rolling, forging, or annealing.

Measurements of the speed of sound are used in determining many properties of materials. The measurement of small changes in the speed of sound is a sensitive method for detecting the presence of impurities in gases and liquids. In solids, measurements of the speed of sound and of the speed’s dependence on various factors permit investigation of, for example, the band structure of semiconductors and the structure of Fermi surfaces in metals. A number of industrial applications of ultrasound in the areas of measurement and inspection are based on measurements of the speed of sound.

The above discussion pertains to the propagation of sound in a continuous medium—that is, the speed of sound is a macroscopic characteristic of the medium. In actuality, materials are not continuous; their discreteness makes it necessary to consider elastic vibrations of other types. In a solid, the concept of the speed of sound pertains only to the acoustical branch of the lattice vibrations.

REFERENCES

Landau, L. D., and E. M. Lifshits. Mekhanika sploshnykh sred, 2nd ed. Moscow, 1953.
Mikhailov, I. G., V. A. Solov’ev, and Iu. P. Syrnikov. Osnovy molekuliarnoi akustiki. Moscow, 1964.
Kolesnikov, A. E. Ultrazvukovye izmereniia. Moscow, 1970.
Isakovich, M. A. Obshchaia akustika. Moscow, 1973.

A. L. POLIAKOVA

The Great Soviet Encyclopedia, 3rd Edition (1970-1979). © 2010 The Gale Group, Inc. All rights reserved.

speed of sound

The speed at which the sound waves travel in a given medium. In the ISA (international standard atmosphere), sound travels at 761.6 mph (equivalent to 1116 ft/s, 340 m/s, 661.7 knots, 34,046.16 cm/s, or 1225.35 km/h). The speed of sound is determined by the density of the medium. In air, it is the temperature that affects the density and thus the speed of sound. See sonic speed.
An Illustrated Dictionary of Aviation Copyright © 2005 by The McGraw-Hill Companies, Inc. All rights reserved

speed of sound

Sound waves travel at approximately 750 mph at sea level, but slow down at higher altitudes. The speed of sound is called "Mach 1." Supersonic refers to speeds from Mach 1 to Mach 5 (1 to 5 times the speed of sound), and hypersonic ranges from Mach 5 to Mach 10 (5x to 10x).
Copyright © 1981-2019 by The Computer Language Company Inc. All Rights reserved. THIS DEFINITION IS FOR PERSONAL USE ONLY. All other reproduction is strictly prohibited without permission from the publisher.
References in periodicals archive ?
Based on your experimental result for the speed of sound compared with the theoretical value at your room temperature, calculate the percentage error.
PVC sheets were used for the measurement of the speed of sound, the ultrasonic transmittance, and the attenuation coefficient of sound waves in PVC material.
[c.sub.x] speed of sound of the material ([C.sub.g] or [C.sub.w]).
A close observation of all the tables reveal that experimental and calculated values of speed of sound are very close to each other indicating the success of PFP model in TMB with THF, TCM and DMSO liquid mixtures.
In a recent study, he and his colleagues showed that after a rock drops into a body of water, a tiny jet of air shoots upward faster than the speed of sound.
But among the diabetic women, only the speed of sound at the phalangeal site correlated significantly with all three BMD values; the speed of sound in the tibia correlated with none of the BMD values, and the speed of sound in the radius correlated with only the BMD of the femoral neck.
Speed of Sound in Bones Lower In Women With Type 2 Diabetes m/sec Type 2 diabetes No diabetes (n =76) (n = 86) Radius 4,044 4,129 Phalanx 3,902 3,999 Tibia 3,815 3,845 Source: Journal of Clinical Endocrinology and Metabolism Note: Table made from bar graph.
Brian Clemenson's seasoned campaigner slides down to the basement level for his race this afternoon and, capable of stepping upon recent performances, Speed Of Sound can score at the chief expense of Raithby Saha.
Despite disappointing reviews of their new album in the US, Chris Martin's Coldplay are vying for Best Group, Best Rock, Best Song for Speed of Sound, Best Album for X&Y, and Best UK and Ireland Act.
The Syncroness chamber will allow scientists to reduce the air pressure that surrounds the track, thus simulating high altitude, and enabling test vehicles to accelerate to velocities of up to eight times the speed of sound.
Japan's trade ministry has said that research will be carried out over the next three years with the aim of building a passenger jet that can fly faster than the speed of sound. Companies from the two countries will invest some JPY200m in the research.