★ When the force is applied tangentially on solid then it experiences a finite deformation and shear stress that is proportional to the deformation. Whereas, when the same shear stress is applied on the surface of fluid then it experiences continuous increasing deformation where, the shear stress is proportional to the rate of change of deformation.

★ The fluid dynamic is dividend in three different areas. They are as follows: Hydrodynamics (flow of liquids), Gas dynamics (flow of gases) and Aerodynamics (flow of air). Whereas, the state of, solid doesn't represent any of the stages.