Example 1.1 Calculating the pressure exerted by a column of liquid
Derive an equation for the pressure at the base of a column of liquid of mass
density ρ (rho) and height h at the surface of the Earth. The pressure exerted by a
column of liquid is commonly called the ‘hydrostatic pressure’.
Method Use the definition of pressure in eqn 1.2 with F = mg. To calculate F
we need to know the mass m of the column of liquid, which is its mass density, ρ,
multiplied by its volume, V: m = ρV. The first step, therefore, is to calculate the
volume of a cylindrical column of liquid.
Answer Let the column have cross-sectional area A; then its volume is Ah and its
mass is m = ρAh. The force the column of this mass exerts at its base is