# 2-1 Sound waves

A ray is directed perpendicular to wavefronts and indicates the direction of
travel of the wavefronts.

A point source emits waves equally in all direction

### Definitions

A wavefront is an imaginary surface over which the displacements of
particles are the same.

Spherical waves

Away from the point source, we can approximate the wavefronts as planes.

Planar waves are waves with planar wavefronts