The waves that occur when the motion of the medium is parallel to the direction of the wave are called longitudinal waves.

Here's why:

* Longitudinal waves involve compressions and rarefactions of the medium. The particles in the medium oscillate back and forth in the same direction as the wave travels.

* Transverse waves involve oscillations that are perpendicular to the direction of wave travel. Think of a rope tied to a post and you shake it up and down – the wave travels along the rope, but the rope itself moves up and down (perpendicular).

Examples of Longitudinal Waves:

* Sound waves: Sound travels through air, water, or solids by compressing and expanding the particles in the medium.

* Seismic P-waves: These are the primary waves generated by earthquakes, which travel through the Earth's interior as longitudinal waves.

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