Here's why:

* Longitudinal waves are waves where the particles of the medium vibrate parallel to the direction the wave travels. This means the particles are compressed and expanded along the same line as the wave's propagation.

* Examples of longitudinal waves:

* Sound waves: Sound travels as vibrations in air, water, or solids. These vibrations are compressions and rarefactions (expansions) of the medium.

* Seismic P-waves: These are the fastest type of seismic waves and travel through the Earth's interior by compressing and expanding the rock.

Contrast with Transverse Waves:

* Transverse waves have vibrations perpendicular to the direction of wave propagation. This means the particles move up and down or side to side, while the wave travels horizontally. Examples include light waves and water waves.