Sound pressure and particle velocity components are always in phase

Evidence

The force required to accelerate the molecules forms the pressure component of the wave. This is associated with the velocity component of the propagating wave and therefore is in phase with it. That is, if the velocity component is a cosine, then the pressure component will also be a cosine. — David M. Howard, Jamie Angus, Acoustics and Psychoacoustics, 161

Categorization

• DEFINE: Clarifies the in-phase relation between pressure and velocity components of a traveling sound wave.
• corroborated: 3 independent passages support this claim — David M. Howard, Jamie Angus, Acoustics and Psychoacoustics, 161
• XREF: connects to: Adjacent in-phase sources boost each piston’s efficiency N-fold through mutual pressure; All acoustic impedances are ratios of force to velocity; Sound waves have an inherent velocity component tied to molecular displacement. (+1 more)

Broader Connections

• A sound wave’s pressure component arises from the force driving molecular displacement. #expands (0.80)
• Sound waves have an inherent velocity component tied to molecular displacement. #expands (0.75)