With the increase or decrease in the temperature of fluids, the viscosity of the fluids changes. At higher temperature, the molecules move faster and at lower temperature, the molecules move at a smaller rate.

Let us consider viscosity of liquid at 00C be 0

Viscosity of liquid at t0C be

Then, viscosity of liquid due to change in temperature can be given by-

0 / = 1 + t1 + t2

Or,

0 = (1 + t1 + t2)

Where,

and  = constants of liquid

Note:

It suggests that viscosity of liquids decrease with the increase in temperature.

For water, the value of viscosity at 00C is

0 = 1.79 x 10-3 poise

Where,

= 33.7 x 10-3

= 22.1 x 10-5

For gases or air, the value of  will be taken as negative

i.e.,

0 =  (1 + t1– t2)

Hence,

0 = 17 x 10-6 poise

Where,

= 56 x 10-9

= 119 x 10-12

It shows that viscosity of gases increase with the increase in temperature. This is because the cohesive force of gases is small as compare to liquids where cohesive forces predominate.

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