Sound pressure is in phase with molecular velocity, not with displacement
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
Category: Causal Relationships
- DEFINE: A core psychoacoustics fact: pressure and velocity are in phase, both quadrature with displacement — often counterintuitive to newcomers.
Related
- Sound pressure and particle velocity components are always in phase (similarity 0.97)
- A sound wave’s pressure component arises from the force driving molecular displacement. (similarity 0.86)
- Excitation in an elastic medium generates waves from the source (similarity 0.84)
- Pressure is scalar while velocity gives a sound wave its direction (similarity 0.84)
- Sound information propagates slower than average molecular speed (similarity 0.83)
- Sound wave molecules have zero velocity at compression peaks due to inertia (similarity 0.82)
- A medium’s density and elasticity relate sound pressure to particle velocity. (similarity 0.82)
- Boom-producing surface motion involves extreme acceleration but modest velocity (similarity 0.81)
- Speed of sound depends on temperature, not pressure (similarity 0.80)
- A small piston still radiates sound because velocity is slightly in phase with force (similarity 0.80)
- Relative phase and path distance determine whether correlated waves cancel or reinforce in space. (similarity 0.79)
- Equal-amplitude sounds in phase double in amplitude while out of phase they cancel (similarity 0.79)
- Sound diffraction arises from gradual pressure decay, not abrupt wave cutoff (similarity 0.79)
- Only accelerating surfaces, not steadily moving ones, generate airborne sound. (similarity 0.79)
- Spreading sound waves weaken because their fixed energy dilutes over an expanding sphere (similarity 0.79)