What is friction and what is its significance in the context of air particle movement?

Friction is a force that opposes motion ... And in the case of air particle movement friction ensures the continuity of flow of the particles

Friction is the resisting force that act on the motion of two surfaces or objects when one objects want to move against another.

Friction opposed the direction of motion by acting opposite the air flow i. e it changes the direction of the air.

Friction also changes air speed. It slow the speed by dragging air across it's surface, hence decreasing air speed.

Explanation:

Friction is the resisting force that act on the motion of two surfaces or objects when one objects want to move against another