For a very good conductor, twice the Poynting flux divided by the speed of light gives the radiation form of this property. Venturi meters can measure the rate of flow by lowering this quantity via a constricted section of a pipe. Electric charge from deformation due to this quantity exemplifies a crystal's piezoelectric property. According to Pascal's principle, this quantity is always evenly distributed in an incompressible fluid. This quantity can be measured in millimeters of mercury or standard atmospheres. For 10 points, name this quantity defined as force per unit area.
a) Pressure
b) Density
c) Velocity
d) Volume