Which type of wave is characterized by particle motion that is parallel to wave motion?

The correct answer is a longitudinal wave, which is defined by the fact that the particle motion occurs parallel to the direction of wave propagation. In longitudinal waves, particles in the medium oscillate back and forth along the same line as the wave travels. This pattern creates regions of compression and rarefaction in the medium.

For instance, in sound waves, air molecules compress together and then spread apart as the wave moves through the air. This parallel movement of particles relative to the direction of the wave is a fundamental characteristic of longitudinal waves.

Understanding the distinction between longitudinal waves and other types of waves is crucial. In contrast, transverse waves feature particle motion that is perpendicular to wave motion, as seen in waves on a string or electromagnetic waves. Surface waves combine characteristics of both types, typically involving circular motion of particles, while seismic waves can include both longitudinal and transverse components, depending on their type. Recognizing these differences helps clarify the mechanics of wave propagation in various mediums.