Answer:
Longitudinal
Step-by-step explanation:
A wave is a periodic disturbance that carries energy, but not matter. Based on the direction of the oscillations of the wave, waves can be classified into two types:
- Transverse wave: in a transverse wave, the direction of the oscillation is perpendicular to the direction of motion of the wave. Examples of transverse waves are electromagnetic waves.
- Longitudinal wave: in a longitudinal wave, the direction of the oscillation is parallel to the direction of motion of the wave. An example of longitudinal wave are sound waves. In a longitudinal wave, regions where the particles of the medium are closer to each other (called compressions) alternate with regions where the particles of the medium are more spread apart (called rarefactions).