why does the viscosity of a gas increase with temperature an

why does the viscosity of a gas increase with temperature? and why does the viscosity of a gas decrease with temperature? ( Fluid mechanics )

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Solution

In gas, molecules have some random motion due to weak intermolecular forces between them. Due to random motion these molecules collide. When the temperature of the gas is increased the kinetic energy in the molecules increases as a result they vibrate more hence the collision between the molecules increase very sharply. As a result of high collision rate , more momentum transfer occurs , resulting in more resistance , hence the viscosity increases. This is the reason why viscosity of gas increases with temperature.

Vice versa when the temperature is decreased the kinetic energy of the molecules decreases, hence collision of the molecules decreases sharply. due to less collision less momentum occurs, resulting in less resistance , hence the viscosity decreases.