Which type of force opposes motion between two surfaces in contact?

Friction is the force that opposes the motion between two surfaces in contact. When two objects are in contact and one tries to move across the other, friction acts in the opposite direction to the motion. This force arises due to the irregularities on the surfaces of the materials in contact, which creates resistance against sliding.

Friction plays a crucial role in our everyday life; it allows us to walk without slipping, enables cars to grip the road while driving, and allows objects to stay put when placed on a slope. If there were no friction, objects would slide freely across surfaces, making it difficult to control movement and stability.

In contrast, inertia refers to an object's resistance to changes in its state of motion, gravity is the force that attracts objects towards each other, particularly towards the earth, and tension is the force transmitted through a string, rope, or wire when it is pulled tight. None of these forces primarily serve to oppose the motion between two surfaces in contact.