In this chapter we will investigate head loss sensitivities due to friction to governing independent variables for steady, incompressible, and fully developed laminar flows through a straight pipe of constant cross-section. We will use the simplified Navier–Stokes equations in cylindrical coordinates by assuming that the velocity components in the tangential and radial directions are zero. The only velocity component of the fluid flowing in the pipe, denoted by U, is in the axial direction, is constant, and only varies in the radial direction r. Also, the pressure gradient along the axial direction of the pipe, $dPdx$⁠, is a constant.