Here's why:

* Longitudinal waves are waves where the particles of the medium oscillate parallel (in the same direction) to the direction the wave travels.

Examples of longitudinal waves:

* Sound waves: Sound travels through air, water, or solids by causing the molecules to compress and expand in the same direction the sound wave moves.

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

In contrast:

* Transverse waves are waves where the particles of the medium oscillate perpendicular to the direction the wave travels. Examples include light waves and waves on a string.