1. Fluid definitions

A fluid is a continuous, deformable, non-rigid material medium that can flow (i.e. undergo large variations in shape) under the action of forces that are all the weaker the slower the variations in shape.

In classical fluid mechanics, fluids are assumed to be homogeneous and isotropic. They can take on the exact shape of the vessels that contain them. They can be deformed with or without resistance. In the first case, the fluid is said to be viscous, while in the second, it is said to be perfect. All real fluids are viscous. However, this property can be more or less pronounced. A gas, for example, can often be equated with a perfect fluid. However, it must be emphasized that, strictly speaking, a gas, even a perfect gas, is not a perfect fluid, but a viscous fluid. Similarly, we will see that in certain situations, the viscosity of a real fluid has no effect on...