Causes of Viscosity:
The causes of viscosity in a fluid are possibly due to two factors (i) intermolecular force of cohesion (ii) molecular momentum exchange.
#Due to strong cohesive forces between the molecules, any layer in a moving fluid tries to drag the adjacent layer to move with an equal speed and thus produces the effect of viscosity.
#The individual molecules of a fluid are continuously in motion and this motion makes a possible process of momentum exchange between layers. Such migration of molecules causes forces of acceleration or deceleration to drag the layers and produces the effect of viscosity.
Although the process of molecular momentum exchange occurs in liquids, the intermolecular cohesion is the dominant cause of viscosity in a liquid. Since cohesion decreases with increase in temperature, the liquid viscosity decreases with increase in temperature.
In gases the intermolecular cohesive forces are very small and the viscosity is dictated by molecular momentum exchange. As the random molecular motion increases wit a rise in temperature, the viscosity also increases accordingly.
The causes of viscosity in a fluid are possibly due to two factors (i) intermolecular force of cohesion (ii) molecular momentum exchange.
#Due to strong cohesive forces between the molecules, any layer in a moving fluid tries to drag the adjacent layer to move with an equal speed and thus produces the effect of viscosity.
#The individual molecules of a fluid are continuously in motion and this motion makes a possible process of momentum exchange between layers. Such migration of molecules causes forces of acceleration or deceleration to drag the layers and produces the effect of viscosity.
Although the process of molecular momentum exchange occurs in liquids, the intermolecular cohesion is the dominant cause of viscosity in a liquid. Since cohesion decreases with increase in temperature, the liquid viscosity decreases with increase in temperature.
In gases the intermolecular cohesive forces are very small and the viscosity is dictated by molecular momentum exchange. As the random molecular motion increases wit a rise in temperature, the viscosity also increases accordingly.
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