The rubbing of one object or surface against another. A physical force that resists the relative motion or tendency to such motion of two bodies in contact. friction. A force on objects or substances in contact with each other that resists motion of the objects or substances relative to each other. ◇ Static friction arises between two objects that are not in motion with respect to each other, as for example between a cement block and a wooden floor. It increases to counterbalance forces that would move the objects, up to a certain maximum level of force, at which point the objects will begin moving.