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A sphere rotating around an axis. Points farther from the axis move faster, satisfying ω = v / r.. In physics, angular frequency (symbol ω), also called angular speed and angular rate, is a scalar measure of the angle rate (the angle per unit time) or the temporal rate of change of the phase argument of a sinusoidal waveform or sine function (for example, in oscillations and waves).
The wave vector and angular wave vector are related by a fixed constant of proportionality, 2 π radians per cycle. It is common in several fields of physics to refer to the angular wave vector simply as the wave vector, in contrast to, for example, crystallography. [1] [2] It is also common to use the symbol k for whichever is in use.
Here we assume that the wave is regular in the sense that the different quantities describing the wave such as the wavelength, frequency and thus the wavenumber are constants. See wavepacket for discussion of the case when these quantities are not constant. In general, the angular wavenumber k (i.e. the magnitude of the wave vector) is given by
for virtually any well-behaved function g of dimensionless argument φ, where ω is the angular frequency (in radians per second), and k = (k x, k y, k z) is the wave vector (in radians per meter). Although the function g can be and often is a monochromatic sine wave, it does not have to be sinusoidal, or even periodic.
This shows a wave with the group velocity and phase velocity going in different directions. The group velocity is positive, while the phase velocity is negative. [1] The phase velocity of a wave is the rate at which the wave propagates in any medium. This is the velocity at which the phase of any one frequency component of the
In physics, angular velocity (symbol ω or , the lowercase Greek letter omega), also known as the angular frequency vector, [1] is a pseudovector representation of how the angular position or orientation of an object changes with time, i.e. how quickly an object rotates (spins or revolves) around an axis of rotation and how fast the axis itself changes direction.
For electromagnetic waves in vacuum, the angular frequency is proportional to the wavenumber: =. This is a linear dispersion relation, in which case the waves are said to be non-dispersive. [1] That is, the phase velocity and the group velocity are the same:
where means the gradient of the angular frequency ω as a function of the wave vector , and ^ is the unit vector in direction k. If the waves are propagating through an anisotropic (i.e., not rotationally symmetric) medium, for example a crystal , then the phase velocity vector and group velocity vector may point in different directions.