Fluid -: A fluid is a substance that is capable of flowing , conform to shape of containing vessel. It also deforms continuously when it issubjected to even a smallest shear stress.
An ideal fluid is frictionless and also it is incompressible .
Viscosity-:It is the property of fluid by virtue of which it offers resistance to shear. Viscosity is caused by cohesive for between molecules of liquid and by collision between molecules of gas .Viscosity is practically independent of pressure and depend upon temperature only .
Unit of viscosity " poise " or 1 gm /cm/ sec.
( 1 poise = 0.1 Ns/ m^2 )
Kinematic viscosity -: It is the ratio of dynamic or absolute viscosity and density. It's unit is stoke . Stoke is equal to 1cm^2/sec.
Newton's law of viscosity -: newton's law of viscosity state that shear stress ( between adjacent layer of fluid) is directly proportional to velocity gradient.
Shear stress = 𝝁 du / dx
( 𝝁 = coefficient of viscosity Pa sec or Ns/ m^2)
du/dx is known as velocity gradient or rate of shear strain and it is zero for fluids at rest. Fluid following newton's law of the viscosity is known as Newtonian fluids and other non - Newtonian fluids. An ideal fluid offers no resistance to flow but real fluid does.
( viscosity is zero for ideal fluid but not for real fluid. )
Surface tension -: Liquid molecules are attracted to each other by equal forces in all directions. On the surface they are subjected to an inward attraction which us not balanced by the outward attraction. This cause the liquid surface to seek a minimum possible area due to surface tension.
Surface tension is also expressed as force per unit length .
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