Displacement Relation in a Progressive Wave

The main difference lies in the direction. We should know that in a longitudinal wave, the displacement of particles is parallel to the direction of wave propagation. In a transverse wave, however, the displacement is perpendicular to the direction of wave propagation.

The units of angular wave number and angular frequency are slightly different.

• Angular wave number k has units of radian per metre (rad/m).
• Angular frequency has units of radian per second (rad/s).

In Physics, we need to know that the phase angle tells us the position of a point within one cycle of a wave. That is measured in radians. It tells you how much a wave is ahead or, behind the other. On the other hand, the initial phase (or phase constant) is the phase angle at time t=0. It tells us where the wave begins with its oscillation cycle.