Ściśliwość gazów (Compressibility of gases)
Properties of gases explained
The kinetic-molecular model helps to explain some of the properties of gases.
Gas particles are spaced far apart relative to one another. Particles are moving with rapid, random motion.
Gases diffuse freely to fill the whole of the containing vessel.
Truly chaotic – the gaseous state
The kinetic-molecular model of gases describes the gaseous state as one in which gas particles are spaced out relative to one another and are moving around with rapid, random motion.
Nieściśliwość cieczy (Incompressibility of fluids)
An incompressible fluid is a fluid whose density does not change when the pressure changes. There is no real incompressible fluid. However, for many flow situations, the changes of density due to changes in pressure associated with the flow are very small. It greatly simplifies the solution of fluid flow equations to treat the the fluid as incompressible.
An incompressible flow is one for which each of the local infinitessimal blobs of fluid has a constant density as it moves through the flow field. The various tiny blobs can each have different densities, but for each one, its density remains constant.
In most cases, since the fluid is usually all the same substance, treating the flow as incompressible is accomplished by taking the density to be the same everywhere in the flow field.