What type of wave is sound?

• A. Transverse
• B. Circular
• C. Surface
• D. Longitudinal

Answer: (D)

Sound is a longitudinal wave, meaning the particles of the medium oscillate in the same direction as the wave travels. As the wave moves, it creates regions of compression where particles are pushed closer together and rarefaction where they spread apart. This back-and-forth motion along the travel direction is why sound propagates as a compressional wave in air, liquids, and tissues. In contrast, a transverse wave has particle motion perpendicular to the direction of travel, which isn’t how sound behaves. Circular or surface descriptors refer more to wavefront shape or motion at boundaries rather than the fundamental particle motion of the wave, so they don’t describe sound’s propagation.