Why Does the Viscosity of Air Increase with Temperature While Water's Decreases?

[stan]

hi all,

does anyone knows why the visciosity of air increases with temp while that of water decreases with temp?

dont the higher temp causes the molecules to vibrate faster, thus allowinh more space to collide with each other, the visciosity should decreases..


thanks for any advice..

stan

 

[FredGarvin]

The viscosity of a gas increases with temperature because of molecular interaction. In gases, molecular collisions transfer momentum between fluid layers. As temperature increases, the molecules move faster and more momentum is transferred between layers (layers of maolecules with a certain velocity), thereby increasing the viscosity.

In a liquid, the viscous effects are from molecular attractions between fluid layers. The higher the temps, the more energy the molecules have to overcome the attractions.