Hello, Sound waves are always introduced as longitudinal mechanical waves: the medium particles oscillate in a direction parallel to the direction of motion of the sound wave. We can only hear sound frequencies between 20Hz and 20KHz. For us to hear these mechanical sound waves, the waves need to be longitudinal to be able to push on our ears' eardrums. A transverse mechanical wave is just a mechanical wave but cannot be called a sound wave. Is that the case? As mentioned, there are transverse mechanical waves. For instance, if we hit the surface of a metal rod (not the end) with a hammer we generate transverse mechanical waves in the rod. These transverse waves produce an oscillation of the rod surface which generates longitudinal sound waves in the neighboring air. Is that correct? When we hear a train that is far away by placing our ears on the train tracks, it is because a mechanical wave ( longitudinal or transverse?) travels inside the metal track and generates a longitudinal sound wave in the air where the observer is. Sound, as a longitudinal wave, can propagate in a liquid, a gas (like air) or inside a solid but the wave needs to be longitudinal to be called sound. That is what I believe. Thanks!