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Consider the streamline flow of an incompressible fluid of density $\rho$ through a pipe of varying height and cross-sectional area. The fluid pressure ($P$), fluid velocity ($v$) and height ($h$) at two points on a streamline are related by \begin{align} P_1+\frac{1}{2} \rho v_1^2+ \rho g h_1 = P_2+\frac{1}{2} \rho v_2^2+ \rho g h_2 \end{align}