The waves that move particles of the medium parallel to the direction in which they are traveling are called longitudinal waves.

Here's why:

* Longitudinal waves: The particles in the medium oscillate back and forth in the same direction as the wave is moving. Imagine a slinky stretched out and then pushed at one end. The compression and expansion of the slinky travel down its length, and the individual coils of the slinky move back and forth parallel to the direction of the wave.

* Transverse waves: In contrast, transverse waves have particles that oscillate perpendicular to the direction of wave travel. Think of a wave on a string. The string itself moves up and down (perpendicular to the direction the wave travels), but the wave itself moves horizontally along the string.

Examples of longitudinal waves:

* Sound waves: Sound waves travel through air, water, and solids by compressing and expanding the medium.

* Seismic P-waves: These are the primary waves that travel through the Earth during an earthquake, and they cause the ground to move back and forth in the same direction as the wave.

Let me know if you have any more questions!