Here's why:

* Longitudinal waves are characterized by the particles of the medium vibrating parallel to the direction the wave travels. This means the particles oscillate back and forth in the same direction as the wave is moving.

Examples of longitudinal waves:

* Sound waves: Sound travels through air (or other mediums) by compressing and expanding the air particles in the direction of the wave's travel.

* Seismic P-waves: These waves are generated by earthquakes and travel through the Earth's interior by compressing and expanding the rock particles.

Contrast with Transverse Waves:

* Transverse waves have particles that vibrate perpendicular to the direction the wave travels. Think of a wave on a string or water waves where the water particles move up and down while the wave travels horizontally.