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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.
In some (unusual) cases both end points of a branch (family) of periodic travelling wave solutions are homoclinic solutions, [37] in which case one must use an external starting point, such as a numerical solution of the partial differential equations. Periodic travelling wave stability can also be calculated numerically, by computing the spectrum.
In the case of a periodic function F with period λ, that is, F(x + λ − vt) = F(x − vt), the periodicity of F in space means that a snapshot of the wave at a given time t finds the wave varying periodically in space with period λ (the wavelength of the wave).
The phase velocity is the rate at which the phase of the wave propagates in space. The group velocity is the rate at which the wave envelope, i.e. the changes in amplitude, propagates. The wave envelope is the profile of the wave amplitudes; all transverse displacements are bound by the envelope profile.
The period (symbol T) is the interval of time between events, so the period is the reciprocal of the frequency: T = 1/f. [ 2 ] Frequency is an important parameter used in science and engineering to specify the rate of oscillatory and vibratory phenomena, such as mechanical vibrations, audio signals ( sound ), radio waves , and light .
An electromagnetic wave travelling through a medium has a propagation delay determined by the speed of light in that particular medium, or ca. 1 nanosecond per 29.98 centimetres (11.80 in) in a vacuum. An electric signal travelling through a wire has an propagation delay of ca. 1 nanosecond per 15 centimetres (5.9 in). [1]
In most cases this is a longitudinal wave of pressure (such as sound), but it can also be a transverse wave, such as the vibration of a taut string. In the case of a sound wave travelling through air, the particle displacement is evident in the oscillations of air molecules with, and against, the direction in which the sound wave is travelling. [2]
Atmospheric waves, associated with a small dust storm of north western Africa on 23 September 2011. An atmospheric wave is a periodic disturbance in the fields of atmospheric variables (like surface pressure or geopotential height, temperature, or wind velocity) which may either propagate (traveling wave) or be stationary (standing wave).