Final answer:
Friction is the resistive force that opposes the relative motion or attempt at motion between two surfaces in contact.
Step-by-step explanation:
The force that resists the relative motion of two surfaces in contact is known as friction. Friction can be described as an external force which always opposes motion or attempted motion between objects in contact. This resistive force arises due to the roughness of the surfaces and also as a result of attractive forces between the molecules making up the two objects. Even when surfaces appear smooth, microscopic irregularities and molecular interactions contribute to frictional resistance. When an object is at rest, static friction keeps it stationary, and when the object is moving, kinetic friction works against the motion.