Viscosity


The internal resistance of liquid to its flow is called its viscosity. Normally, viscosity is denoted by Greek word eta (η). Different liquids have different viscosity due to presence of intermolecular attractions. Liquids that have weaker intermolecular attraction have less viscosities. Liquids that have stronger intermolecular attraction have greater viscosities. Ethyl alcohol (CH3CH2OH) is more viscous than ether (C2H5.O.C2H5) because there are hydrogen bonds among the ethyl alcohol molecules. Viscosity of a liquid decreases with increasing of temperature because by increasing temperature, the volume of liquid increases and intermolecular attraction become weaker.

Units of Viscosity:  
The measuring unit of viscosity is “Poise” with the dimension gm/cm (1 Poise = 1gm/cm). The S.I unit is Newton x Second per square metre (N.S.m-2).

Viscosity (centipoise) at different temperatures.

Liquid
Viscosity
0 °C
20 °C
50 °C
Water
1.789
1.005
0.55
Ethyl alcohol
1.78
1.19
0.701
Glycerine
12100
1499
-------
Acetone
0.395
0.322
0.246

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