here's one from my side...

its a very simple n basic concept but sometimes we do misunderstand n apply it incorrectly.

 

>>>force of friction decides the relative motion between two bodies only at their surface of contact i.e. the surface at which force of friction acts. It decides whether the body will move "with respect to" that surface or not . It does not governs the overall motion of body.

 

A body may be at rest with respect to a surface but may be in motion otherwise.

 

 

its a very basic concept n probably u knew it before...but even if it helped to one of u then i'm pleased!.