Here's why:
* Longitudinal waves: The particles in the medium oscillate back and forth *parallel* to the direction the wave travels. Think of a spring: when you push one end, the compression travels along the spring, and the individual coils of the spring move back and forth in the same direction the compression travels.
* Transverse waves: In contrast, particles in a transverse wave vibrate *perpendicular* to the direction the wave travels. Imagine a rope: when you shake one end, the wave travels along the rope, but the individual segments of the rope move up and down (or side to side), perpendicular to the direction the wave travels.
Examples of Longitudinal Waves:
* Sound waves
* Seismic P-waves (pressure waves)
Examples of Transverse Waves:
* Light waves (electromagnetic waves)
* Water waves (surface waves)
* Seismic S-waves (shear waves)
