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The speed of sound is the distance travelled per unit of time by a sound wave as it propagates through an elastic medium. More simply, the speed of sound is how fast vibrations travel. At 20 °C (68 °F), the speed of sound in air, is about 343 m/s (1,125 ft/s; 1,235 km/h; 767 mph; 667 kn), or 1 km in 2.91 s or one mile in 4.69 s.
The speed of sound in any chemical element in the fluid phase has one temperature-dependent value. In the solid phase, different types of sound wave may be propagated, each with its own speed: among these types of wave are longitudinal (as in fluids), transversal, and (along a surface or plate) extensional. [1]
Dimensionless numbers (or characteristic numbers) have an important role in analyzing the behavior of fluids and their flow as well as in other transport phenomena. [1] They include the Reynolds and the Mach numbers, which describe as ratios the relative magnitude of fluid and physical system characteristics, such as density, viscosity, speed of sound, and flow speed.
v = speed of sound, ρ = volume density of medium kg m −2 s −1 [M] [L] −2 [T] −1: Specific acoustic impedance z = S = surface area kg s −1 [M] [T] −1: Sound Level: β = | | dimensionless dimensionless
where is the Laplace operator, is the acoustic pressure (the local deviation from the ambient pressure), and is the speed of sound. A similar looking wave equation but for the vector field particle velocity is given by
The speed of sound depends on the medium the waves pass through, and is a fundamental property of the material. The first significant effort towards measurement of the speed of sound was made by Isaac Newton. He believed the speed of sound in a particular substance was equal to the square root of the pressure acting on it divided by its density:
ρ is the volumetric mass density of the medium; c is the speed of the sound waves traveling in the medium; δ is the particle displacement; x is the space variable along the direction of propagation of the sound waves. This equation is valid both for fluids and solids. In fluids, ρc 2 = K (K stands for the bulk modulus);
V is the volume of interest; p is the sound pressure; v is the particle velocity; ρ 0 is the density of the medium without sound present; ρ is the local density of the medium; and; c is the speed of sound.