I) There are several terms in mechanics that distinguishes the observable universe into two parts, the following are some such classifications,
a) Homogenous and In-homogeneous
Homogenous materials are those which cannot be disjointed mechanically nor separated into two or more different constituents, for example, polypropylene is one such material, steel is also homogeneous. At the same time there are other materials like powder coated steel which can be subjected to mechanical separation and hence can be considered as in-homogeneous.

b) Isotropic and Anisotropic
Isotropic material is the one whose properties do not change with direction and anisotropic material is the one whose properties do depend on the direction (properties changes with direction of the material). Glass metals are some examples whose properties are isotropic and wood is an example whose properties are mainly anisotropic in nature.

c) Elastic and Inelastic
Once deformed from its original shape by external application of the forces, if the body managed to return to its original shape, it is called elastic material and if it could not get back into the original shape after the removal of the external forces, then it is called as inelastic material. Examples of the elastic materials include rubber. Inelastic material an iron rod.

d) Viscid is also called as viscous flow, where in the fluid flow is characterized and controlled by the viscous forces acting between different layers and the in viscid is the one with no any viscous forces acting in it. Example of the viscid flow include flow of paste or any other viscous solutions, flow of gas is an example of in viscid flow.

e) Compressible and incompressible – when the fluid is not compressible in the operating temperature and pressure conditions and then its properties will be guided by a set of different equations and when the same fluid is operated by in pressure and temperature conditions where it will be subjected to compression then it is called as incompressible fluids. Same substance can also behave like compressible and incompressible too. Air in the normal breathing pressure ranges, behave like incompressible and at the same time, if it is employed for filling the tyres, its nature can be considered incompressible.

f) Static or Dynamic

Static conditions are those conditions where in there won’t be consideration to the motion in the force analysis further the loads are considered to be in the state of fixed conditions and they wont change with time. Dynamic conditions refers to the condition of the variability in the force conditions as well as in the condition of the body. Example of static condition refers to the stresses acting on a structural frame supporting an electric cable(neglecting the wind effect). Dynamic conditions refer to a spring compressed with load varying with time.

g) Steady and unsteady state
If the properties of the system do not change with time, then they are called as in steady state and if the properties do change with time they are called as in unsteady state.

1. Many terms in mechanics seem to divide the universe into two par...