The most important difference between these two types of fluid is in their relative compressibility. There are two types of fluid: liquids and gases.

This provides us with a characterizing feature of liquids (and gases-fluids, in general) that distinguishes them from other forms of matter, and we can thus give a formal definition. Furthermore, the more stress that is applied, the more the fluid element will deform. For example, if one were to impose shear stress on a fluid element, the fluid element deforms because it cannot withstand any tendency of applied shear stress to change its shape. Phase diagram of water.Д«y definition, a fluid material possesses no rigidity at all. Its original shape when the stress is relieved. However, the critical shear stress above which it yields is relatively small, and once this stress is exceeded, the material deforms continuously and irreversibly and does not recover To be more exact, when shear stress is first applied to a rigid material, it deforms slightly but then springs back to its original shape when the stress is relieved.ДЄ plastic material, such as clay, also possesses some degree of rigidity.

For example, if one were to impose shear stress on a solid steel block, the block would not begin to change shape until an extreme amount of stress has been applied. Fluids are a subset of the phases of matter and include liquids, gases, plasmas, and, to some extent, plastic solids.Д«y definition, a solid material is rigid. The characteristic that distinguishes a fluid from a solid is its inability to resist deformation under applied shear stress (a tangential force per unit area). In physics, a fluid is a substance that continually deforms (flows) under applied shear stress.

Power definition