The equations of conservation of mass, momentum, and energy describe all types of fluid flows — from the water flow inside a washing machine to the flow of air over a space shuttle re-entering the Earth's atmosphere at approximately 36 times the speed of sound! If you are thinking there is no way the movement of water inside a washing machine is comparable to that of air flow over a space shuttle, you are absolutely right. But we can make certain simplifying assumptions in each case that show these examples have more in common than you might think. Simplifying the problems can make them easier to solve.
As an example of simplification, the air flow over a drone can be considered as an incompressible flow.
Also, the water flow through a pipe, after a certain distance from the starting point, can be considered to be mostly one-dimensional. In this lesson, we present simplifying fluid flow assumptions and their physical meaning.