Concept:Friction is a force that opposes the relative motion between two surfaces in contact. It is useful in many daily activities.Explanation:- Writing is possible because friction between the pen tip and paper prevents slipping.- Walking works because friction between feet and ground provides grip.- Brakes stop a vehicle by creating friction between brake pads and wheels.- A ball thrown upward returns due to gravity, not friction. So example C is incorrect.Thus, correct examples are A, B, and D.
