Springs and waves


With springs of this kind we can emphasize the difference between longitudinal and transverse waves. The first waves are obtained by giving, with swift motions of the hand, impulses parallel to the spring axis; the second ones by giving impulses perpendicular to the axis.

Note how in longitudinal waves (clip A) the oscillations have the same direction of the wave propagation, while in transverse waves (clip B) the oscillations are in a plane perpendicular to the propagation direction.

Clip A
Wave phenomena similar to those discussed occur frequently in nature. For instance, if you hit the end of a rod, the matter in it starts oscillating and waves are created, both transverse and longitudinal: in this case the oscillations have the effect of compressing and rarefying the air around the rod, thus producing a sound.
Clip B