Which type(s) of sound wave modes will propagate through liquids?

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

Answer: (D)

In liquids, sound travels as a longitudinal (compressional) wave, where particle motion is in the same direction as the wave travels. Liquids have very little shear rigidity, so they cannot support transverse motion where particles move perpendicular to the direction of travel. That’s why transverse waves don’t propagate through liquids. Rayleigh and surface waves are types of waves tied to surfaces and typically require a solid to support the required shear interactions; they aren’t bulk acoustic modes that propagate through a liquid. Therefore, the only bulk wave type that propagates through liquids is longitudinal.