Unless otherwise noted, the types of fluid flows we will consider are those that are:

• Nonviscous: There is no loss of energy due to internal friction between adjacent layers of the fluid.
• Steady State: At any point in the fluid, the velocity and pressure do not change with time -- they have reached steady state equilibrium.
• Non-turbulent: The fluid has no net angular momentum about any point in the fluid -- there are no eddies in the flow. We usually call this type of flow to be a laminar flow.

These conditions are rarely encountered in the real world. For example, water flowing through a pipe will always have some drag force on it at the pipe boundary where the water is in contact with the wall of the pipe. None-the-less, the above condition can be and are a good first order approximation. A good course in Fluid Mechanics would not neglect the effects.