section_path: Wave in elastic medium/Phase velocity and group velocity
section_name: Phase velocity and group velocity
paragraph_text: Phase velocity and group velocity
  
  There are two velocities that are associated with waves, the phase velocity and the group velocity.
  
  Phase velocity is the rate at which the phase of the wave propagates in space: any given phase of the wave (for example, the crest) will appear to travel at the phase velocity. The phase velocity is given in terms of the wavelength λ (lambda) and period T as v p = λ T. {\displaystyle v_{\mathrm {p} }={\frac {\lambda }{T}}.}
  
  Group velocity is a property of waves that have a defined envelope, measuring propagation through space (that is, phase velocity) of the overall shape of the waves' amplitudes—modulation or envelope of the wave.