Physics » Mechanical Waves and Sound » Summary of Longitudinal Waves

Summary and Main Ideas


  • A longitudinal wave is a wave where the particles in the medium move parallel to the direction in which the wave is travelling.

  • Most longitudinal waves consist of areas of higher pressure, where the particles in the medium are closest together (compressions) and areas of lower pressure, where the particles in the medium are furthest apart (rarefactions).

  • The wavelength of a longitudinal wave is the distance between two consecutive compressions, or two consecutive rarefactions.

  • The relationship between the period (T) and frequency (f) is given by

    \[T = \frac{1}{f}\]


    \[f = \frac{1}{T}\]

  • The relationship between wave speed (\(v\)), frequency (\(f\)) and wavelength (\(λ\)) is given by

    \[v = f \lambda\]

Table: Units used in longitudinal waves

Physical Quantities


Unit name

Unit symbol

Amplitude (A)



Wavelength (λ)



Period (T)



Frequency (f)


\(\text{Hz}\) (\(\text{s$^{−1}$}\))

Wave speed (v)

metre per second


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