A fluid is defined as a substance that continually deforms when shear forces are applied regard-less of how small the shear forces may be. It has no definite shape of its own.It experiences relative motion between their elementary parts as long as shearing forces are present. It includes liquids, gases, plasma and to some extent plastic solid.It is the branch of continuum mechanics that examines the nature and properties of Fluids, both at rest and in motion.