The waves that move back and forth in the same direction in a medium, are known as longitudinal waves.
Example: Sound waves.
A compression zone inside a longitudinal wave will be where the atoms are nearest to each other, and a rarefaction region in such a longitudinal wave would be where the elements are separated widely.
Properties of longitudinal waves:
Since longitudinal waves require a medium to propagate, they constitute mechanical waves.
Compressions, as well as rarefactions, are indeed the two components of longitudinal waves that have been observed whenever they travel through a medium.
Whenever molecules or elements are further apart, rarefaction occurs.
Whenever particles are near to one another, they compress.
