Viscosity

  • Viscosity of a fluid is a measure of its resistance to shear or angular deformation.

  • Lubricating oil, for example, has high viscosity and resistance to shear, is cohesive, and feels sticky, whereas gasoline has low viscosity.

  • Lesser the viscosity of the fluid, the greater is its ease of movement (fluidity). The reciprocal of viscosity is fluidity.

  • All real fluids have some resistance to stress and therefore are viscous, but a fluid which has no resistance to shear stress is known as an ideal fluid or inviscid fluid.

  • Poise (P) is the unit of viscosity. 1 P = 1 g/(cm.s) 1 cP = \(1\times10^{-2}\) P = 0.01 g/(cm.s)
    = \(0.01\times10^{-3}\) kg/(\(10^{-2}\)m.s) = 0.001 kg/(m.s)

  • Viscosity of water at 20\(^\circ\)C = 1 cP.

  • Viscosity of air is roughly 50 times smaller than the viscosity of water at the same temperature.

  • Viscosity of honey = 2000 – 10000 cP