Frictional force opposes relative motion between surfaces
Explanation:
Friction that exists when the object is not moving is called static friction. In static friction ,If we are applying a force in the object the frictional force is in the opposite direction . If it is not the case, there have been some net force and the object starts accelarating.
The main component of the contact force of two objects is normal force and that is in the perpendicular direction. Frictional force is other complnent. This frictional force is parallel to the interface between objects. Frictional force opposes relative motion between surfaces.
