Sound waves are classified as longitudinal waves because the individual particles of the medium oscillate back and forth in a direction parallel to the direction of sound propagation.

Rarefactions (R) are the regions where the coils of a slinky are further apart.

In longitudinal waves, particles of the medium move in a direction parallel to the direction of propagation of the disturbance.

The regions where the coils become closer are called compressions (C).

The movement of vibrating objects creates pressure variations in the medium, leading to the propagation of sound waves.