What does the term 'friction' refer to in mechanics?

In mechanics, 'friction' is defined as a resistance force that acts between two surfaces in contact, opposing the relative motion or attempted motion of an object. This resistance occurs due to the interactions at the microscopic level between the surfaces, which can include roughness and adhesion. Friction is crucial in many physical situations, as it affects how objects move and interact.

When considering the context of motion, friction plays a key role in processes such as walking or driving, where it provides the necessary grip. Without sufficient friction, for example, a car would have difficulty accelerating or stopping. Therefore, the definition that identifies friction as a resistance to the movement of an object accurately captures its fundamental nature and role in mechanics.