Microscopic Phenomena of Forces

Friction always opposes the motion or attempted motion between objects in contact. Friction arises in part because of the roughness of the surfaces in contact. A force is required just to set the object in motion. Much of the friction is actually due to attractive forces between molecules making up the two objects so that even perfectly smooth surfaces are not friction-free (even though they can be considered as such, for simplicity). An object will move freely, either by removing the roughness of the surface or by applying a large and explosive force - compared to the friction - that doesn't allow the surfaces to bond.