Wave number

A number that determines the spatial periodicity of a wave (i.e., the distance required for a wave shape to repeat itself) —

\begin{align} \label{eq:12601a} k_w &= \frac {2 \pi \,f}{C} \\[0.7em]%eqn_interline_spacing &= \frac {2 \pi}{\lambda} \nonumber \end{align}

where —

\( k_w \)	= wave number
\( f \)	= frequency of oscillation
\( C \)	= wave speed
\( \lambda \)	= wavelength

The wave speed \( C \) must be appropriate for the type of wave that is being evaluated. Examples:

• For a pressure wave in a thin rod, the thin-wire wave speed \( c_{tw} \) must be used.
• For a pressure wave in an infinite medium, the dilatational wave speed \( C_{d} \) must be used.

Reference: Kinsler, p. 36