The speed of sound is the propagation speed of the weak pressure disturbance in the medium, and its size varies according to the nature and state of the medium. The speed of sound in the air is about 340 m/s at 1 standard atmospheric pressure and 15°C.


The propagation speed of sound wave in elastic medium is sound speed, its symbol is c, unit is m/s: c=λf

In the formula, f is the vibration frequency, that is, the number of vibrations per second, Hz: λ is the wavelength, m.


Because there is no shear elasticity in the gas, only volume elasticity, so the propagation form of the gas can only be longitudinal waves. In other words, under the disturbance of sound waves, the particles in the gas medium vibrate near their respective equilibrium positions, forming a dense and sparse successive transmission process. At the same time, the moving direction of the particle is the same as the propagation direction of the wave. In general, the sound velocity expression of a gas under any circumstances is quite complicated. Its expression is related to the relative molecular mass, specific heat capacity, and physical property equations of the gas, and will not be introduced here. In general problems, the sound velocity formula of an ideal gas is often used.


It can be proved that the sound velocity in an ideal gas is: c=(rp/p)0.5 In the formula, r adiabatic coefficient is equal to the ratio of heat capacity at constant pressure to heat capacity at constant pressure; p is gas pressure, Pa; ρ is density, kg/m3.


Propagation speed in different media

Vacuum 0m/s (that is, it cannot be transmitted);

Air (15℃) 340m/s;

Air (25℃) 346m/s;

Cork 500m/s;

Kerosene (25℃) 1324m/s;

Distilled water (25℃) 1497m/s;

Seawater (25℃) 1531m/s;

Copper (rod) 3750m/s;

Marble 3810m/s;

Aluminum (rod) 5000m/s;

Iron (rod) 5200m/s;