<human>: What are the different types of acoustic waves?
<bot>: The different types of acoustic waves include longitudinal, shear, surface and bulk acoustic waves. Longitudinal waves are compressional waves that travel through a medium in the direction of propagation. Shear waves are transverse waves that move perpendicular to the direction of propagation. Surface waves are guided waves that propagate along the surface of a solid material. Bulk acoustic waves are pressure waves that propagate through a fluid or gas.