group velocity

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Group velocity

The velocity of propagation of a group of waves forming a wave packet; also, the velocity of energy flow in a traveling wave or wave packet. The pure sine waves used to define phase velocity vp do not ever really exist, for they would require infinite extent. What do exist are groups of waves, wave packets, which are combined disturbances of a group of sine waves having a range of frequencies and wavelengths. Good approximations to pure sine waves exist, provided the extent of the media is very large in comparison with the wavelength of the sine wave. In nondispersive media, pure sine waves of different frequencies all travel at the same speed vp, and any wave packet retains its shape as it propagates. In this case, the group velocity vg is the same as vp. But if there is dispersion, the wave packet changes shape as it moves, because each different frequency which makes up the packet moves with a different phase velocity. If vp is frequency-dependent, then vg is not equal to vp. See Phase velocity, Sine wave, Wave motion

McGraw-Hill Concise Encyclopedia of Physics. © 2002 by The McGraw-Hill Companies, Inc.

group velocity

[¦grüp və′läs·əd·ē]
The velocity of the envelope of a group of interfering waves having slightly different frequencies and phase velocities.
McGraw-Hill Dictionary of Scientific & Technical Terms, 6E, Copyright © 2003 by The McGraw-Hill Companies, Inc.
References in periodicals archive ?
Group velocities were determined using longitudinal velocity of 2850 m/s and a shear wave velocity of 1980 m/s [16].
Here [V.sub.S] and [V.sub.A] are the group velocities, respectively, of [S.sub.0] and [A.sub.0] modes.
Figure 7 compares the [A.sub.0] mode's group velocities obtained from the theory, simulation, and experiment at 50, 100, and 150 kHz.
the frequency-velocity matrix) reported in Figures 6c and 6d are normalized frequency by frequency so to easily identify the group velocities for each frequency regardless of the amplitude of each specific frequency, which clearly depends on the characteristics of the adopted source and on the attenuation produced by the soil properties.
Based on the Debye model, Peterson first applied the MC method to solve thermal transport in a one-dimensional model by simplifying the phonon group velocities and polarization [29].
Dispersion curves were given by the derivation of longitudinal wave equations to provide group velocities and modes against the input frequencies of guided waves in rock bolts.
The group velocity of SH wave is solved as the velocity of shear vertical wave [c.sub.T] [16], while the group velocities of Lamb waves are solved from the Rayleigh-Lamb equation [17]:
The above-described group velocities constitute the dispersion curves to be considered for regionalization.
Material, Rod Geometry, Group Velocities and Pencil Lead Breaks