Equation 15.2 applies to any fluid in a uniform gravitational field: Equation 15.3 follows from Equstion 15.2 for the special case of a liquid . It's also possible to integrate Equation 15.2 to find the pressure in a gas that's subject to the gravitational force.Because the gas density isn't constant,this is s little more involved mathematically.Problem 68 explores the variation of pressure with height in Earth's atmosphere.