The Fermi wave-vector is proportional to the cube-root of one form of this value for electrons. The continuity equation for fluids has a term for its time derivative. In a barotropic fluid, the pressure is only a function of this quantity, which is constant for an incompressible fluid. According to Pascal's law, the change in pressure is equal to g delta h times this value. For an ideal gas, this property is equal to P times the molecular weight over RT. Specific gravity is a ratio of this to a 
The Fermi wave-vector is proportional to the cube-root of one form of this value for electrons. The continuity equation for fluids has a term for its time derivative. In a barotropic fluid, the pressure is only a function of this quantity, which is constant for an incompressible fluid. According to Pascal's law, the change in pressure is equal to g delta h times this value. For an ideal gas, this property is equal to P times the molecular weight over RT. Specific gravity is a ratio of this to a reference value of this quantity. This value is symbolized by a lowercase rho. For 10 points, name this property that, for mass, is the mass per unit volume.
The Fermi wave-vector is proportional to the cube-root of one form of this value for electrons.
density [prompt on rho before mentioned; or electron density]