Essay On Viscosity

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Newton’s Law of viscosity Viscosity is the property of a fluid which offers resistance due to the movement of one layer of fluid over another adjacent layer of fluid. The top layer causes a shear stress on the adjacent lower layer while the lower layer causes a shear stress on the adjacent top layer. So the viscosity is a measure of the internal fluid friction which causes resistance to flow. It is primarily due to cohesion and molecular momentum exchange between fluid layers and as flow occurs, these effects appear shearing stresses between the moving layers of fluid. An ideal fluid has no viscosity. There is no fluid which can be classified as a perfectly ideal fluid. However, the fluids with little viscosity are sometimes considered as ideal fluids. …show more content…

Types of Fluids
(i) ideal Fluid A fluid which is incompressible and is having no viscosity is known as ideal fluid. Ideal fluid is only an imaginary fluid as all the fluids, which exist, have some viscosity.
(ii) Newtonian Fluids The fluids which obey the Newton’s law of viscosity i.e. a linear relationship between the stress tensor and rate of strain tensor(τ=μ du/dy ), are called Newtonian fluids. These fluids are represented by a straight line on a graph between the components of shearing stress and rate of strain. The slope of line is represented by material constant μ i.e. coefficient of viscosity. In general this constant is a function of material properties like temperature and density. For such fluids, μ does not change with rate of deformation.

(iii) Non- Newtonian Fluids The fluids which do not obey the Newton’s law of viscosity i.e. fluids which do not follow the linear relationship between shear stress and rate of deformation are termed as Non-Newtonian fluids.
Examples: oil, rubber, plastic, ink, honey, blood

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