Incompressibility

Incompressibility means the property of a substance under pressure to show no change in volume, so do not can be compressed. The volume here consists of getting the same number of particles. All real materials are compressible. Solids and liquids are nearly incompressible compared to gases and are used for mathematical simplification to gases considered as incompressible. Gases at atmospheric pressure have a higher by a factor of 1000-10000 compressibility than most liquids. Liquids are usually ten times more compressible than solids.

During the isothermal compressibility for fluids usually provided as the size, you are in solids to the reciprocal of the isothermal bulk modulus. So incompressibility stands for the approximation of an infinitely high compression module. Incompressible body experienced by pressure change no change in volume. However, you may experience a change in shape. Rubber is often considered as incompressible because the bulk modulus is very large compared to the shear modulus.

To simplify mathematical equations, under the assumption of an incompressible fluid, the following mathematical formulation used in hydrodynamics for the incompressibility:

The current speed. This relationship is called divergence freedom.

The picture above right is trying to make this connection. It can be seen that, for example, on both sides with horizontal flow of the velocity component and the volume element into simultaneous vertical flow has a velocity component with the result immediately.

Equation (1) was determined using the continuity equation:

Derived. For incompressible flow is the definition for a particle that its density does not change:

The comparison of (2) and (3) leads directly to equation (1).