A medium’s density and elasticity relate sound pressure to particle velocity.

Evidence

The velocity and pressure components of a sound wave are also related to each other in terms of the density and springiness of the propagating medium. — David Howard, Jamie Angus, coustics and Psychoacoustics, 147

Categorization

• QUESTION: This paragraph is cut off mid-sentence — worth reading the continuation to see how density and springiness map onto acoustic impedance.