**Newton’s law of viscosity**:-

According to Newton’s law of viscosity does hair trace on a layer of a fluid is directly proportional to the rate of shear strain.

**The following important points may be noted for viscous flow**

a) fluid which has no viscosity is known as ideal fluid

b) a fluid has a viscosity is known as aerial fluid.

c) a fluid whose viscosity does not change with the rate of deformation or Shear Strain is known as newtonian fluid.

d) a fluid whose viscosity change with the rate of defamation or Shear Strain is known as non newtonian fluid

e) a flow in which the viscosity of fluid is dominating over inertia forces is called laminar flow. It take place at very low velocities..

f) iflow in which the inertia force is dominating over the is called turbulent flow. It take place at high velocities.

g) wct at which the flow changes from the laminar flow to the turbulent flow is called 8 critical velocity. It is of two types otherwise lower critical velocity and higher critical velocity. The velocity at which the laminar flow stop is known as lower critical velocity velocity at which the turbulent flow start is known as higher critical velocity.

h) the ratio of inertia force to the viscous force is called Reynolds number. The flow in a pipe is laminar when Reynolds number is 2000 less than and flow is turbulent flow in real number is more than 2800. But when Reynolds number is between 2000 and 2800 the flow is neither laminar nor turbulent…

i) the velocity corresponding to Reynolds number of 2000 is called lower critical velocity and the velocity corresponding to Reynolds number of 2800 is called higher critical velocity.

j) the loss of head due to velocity of laminar flow in pipe is…

** ****H _{L} = 32μvl / wd^{2}**

μ – viscosity of the liquid.

v- velocity of the liquid in the pipe.

l- length of pipe.

d- diameter of pipe.

w- specific weight of the following liquid.

k) the loss of head due to friction in a pipe of uniform diameter in which a viscous flow is taking place is 16 / Rn,

where, Rn is Reynolds number.