What type of wave features particle vibrations that are parallel to the wave's direction of travel?

In a longitudinal wave, particle vibrations occur in the same direction as the wave is moving. This means that as the wave propagates, particles of the medium compress and rarefact in the same line as the wave travels. This characteristic is crucial for understanding sound waves, which are a common example of longitudinal waves. The movement of air particles as sound waves propagate illustrates this principle, as they move back and forth in the direction of the wave's travel, creating compressions and rarefactions.

Other types, such as transverse waves, feature particle vibrations that occur perpendicular to the direction of wave travel, which is not the case here. Consequently, while surface waves and mechanical waves also exist, they either combine features of longitudinal and transverse waves or pertain more broadly to wave types in physical media but do not specifically define the parallel particle motion noted with longitudinal waves.