For all fluids viscosity changes with temperature.

For liquids: µ_{0} / µ = 1 + at + βt_{2}

Where µ_{o} = viscosity of liquid at 0^{o}c, in poise

µ= viscosity of liquid at t° C in poise

a, β = constants for the liquid.

From equation (1.2) we see that viscosity of liquid decreases with increase of temperature.

For water: µ_{o} = 1.79 x 10_{-3}poise, a= 33.7 x 10_{-3}, β = 22.1 x 10_{-5}

For gases : µ = µ_{o} (1 +at – βt^{2}) … (1.3)

For air: µ_{o} = 17 x 10_{-6} poise, a= 56 x 10_{-9}, β = 119 x 10_{-12}

From equation (1.3), we see that viscosity of gases increases with the increase of

temperature because in case of gases the cohesive force is small and molecular momentum

transfer predominates whereas in liquid molecular momentum is small and cohesive

force predominates.