For 10 points, name this quantity equal to force over area, measured in pascals.
When this quantity is divided by specific weight and measured in units of length, it's called its namesake "head." Compressibility equals the partial derivative of volume with respect to this quantity, divided by volume. One form of this quantity can be calculated as the product of fluid density, gravity, and the height below the surface. This quantity equalizes in all locations of an incompressible fluid according to Pascal's principle. Work done by a gas equals this quantity times its change in volume. At constant height, an increase in fluid velocity will lead to a decrease in this quantity. For 10 points, name this quantity equal to force over area, measured in pascals.
When this quantity is divided by specific weight and measured in units of length, it's called its namesake "head.
pressure [or pressure head; or gauge pressure; or hydrostatic pressure]