At this point, the molecule is experiencing the least pressure. Of course, this is the opposite for molecules to the reed s left. Waves that move in the same direction, or parallel to, their source are called longitudinal waves. Longitudinal sound waves are the easiest to produce and have the highest speed, however, it is possible to produce other types. Waves which move perpendicular to the way their source does are called shear waves.
Shear waves travel at slower speeds than longitudinal waves, and can only be made in solids.
Another type of wave is the surface wave. Surface waves travel at the surface of a material and move in elliptical orbits. They are slightly slower than shear waves, but difficult to make. A final type of sound wave is the plate wave. These waves also move in elliptical orbits, but are much more complex.