Abstract
Several practical problems of Fluid Dynamics can be solved with the use of the linear momentum balance equation, mostly in integral form. We select an appropriate control volume and evaluate all the forces acting on it, separating the surface forces (acting on the outer surface of the control volume), and the volume forces (acting on the fluid particles contained in the volume). For ideal fluids (zero viscosity), only pressure is present and the surface forces are normal to the external surface. The volume forces are the weight, the local inertia (in unsteady flows) and the apparent forces (e.g., centrifugal, Coriolis, Euler), defined in non-inertial control volumes.
