Acoustic impedance is the
Acoustic impedance is the ratio between this quantity and the product of velocity and the surface area. One type of this quantity scales with the electron number density raised to the five- thirds in the classical limit, but density raised to the four-thirds in the relativistic limit. Dividing Poynting's vector by the speed of light gives another form of this quantity. The partial derivative of this quantity with respect to density is the speed of sound squared. This scalar quantity is defined to be the negative average of the normal stresses in a fluid. Multiplying fluid density, gravitational acceleration, and height gives the hydrostatic form of it, which is often measured in torr, or millimeters of mercury. For 10 points, name this quantity equal to force divided by area.
Acoustic impedance is the ratio between this quantity and the product of velocity and the surface area.
pressure [or radiation pressure; or hydrostatic pressure; or electron degeneracy pressure; or sound pressure]