# why we learn fluid mechanics?

Fluid mechanics is essentially the study of fluids either in motion (fluid in dynamic mode) or at rest (fluid in stationary mode). A fluid is defined as a material that continuously deforms under a constant load. There are five relationships that are most useful in fluid mechanics problems: kinematic, stress, conservation, regulating, and constitutive. The analysis of fluid mechanics problems can be altered depending on the choice of the system of interest and the volume of interest, which govern the simplification of vector quantities. By assuming that a fluid is a continuum, we make the assumption that there are no inhomogeneities within the fluid. Viscosity relates the shear rate to the shear stress. Definition of a fluid as Newtonian depends on whether the viscosity is constant at various shear rates. Newtonian fluids have constant viscosities, whereas non-Newtonian fluids have a non-constant viscosity. For most biofluid applications, we assume that the fluid is Newtonian.

The phenomena of fluid motion are governed by known laws of physics–conservation of mass, the laws of classical mechanics (Newton’s laws of motion), and the laws of thermodynamics. These can be formulated as a set of nonlinear partial differential equations, and in principle one might hope to infer all the phenomena from these. In practice, this has not been possible; the mathematical theory is often difficult, and sometimes the equations have more than one solution, so that subtle considerations arise in deciding which one will actually apply. Understanding of fluid mechanics is essential for engineer that work in oil and gas industry.

When an engineer conduct troubleshooting related to fluid mechanics, he need to understand the whole system. Usually, an engineer will find system information in PSI ( Process Safety Information ) Documents. PSI Document consist of Process flow diagram, PID and other drawing.