The study of fluid behavior (liquids, gases, blood, and plasmas) at rest and in motion is known as fluid mechanics. Fluid mechanics has numerous applications in mechanical and chemical engineering, as well as biological and astrophysical systems. Kinematic, stress, conservation, regulating, and constitutive relationships are the five relations that are most useful in fluid mechanics problems.
As most of the compounds treated in chemical engineering are in the form of a fluid, whether liquid or gas, fluid mechanics is essential. Petroleum and petroleum products, for example, are fluids in a refinery. Fluids have diverse qualities that must be understood in order to effectively handle them.