When a body slides over a rough surface, the contact force that resists or opposes the relative motion between the two surfaces is called ______.

Introduction / Context:

Whenever two surfaces are in contact and one tries to move relative to the other, a resistive force called friction appears at the interface. Friction plays a crucial role in everyday life, allowing us to walk without slipping and vehicles to move on roads. This question asks for the correct name of the force that resists sliding motion between surfaces, checking your understanding of basic contact forces in mechanics.

Given Data / Assumptions:

• A body is sliding or trying to slide over a surface.
• The surfaces are rough to some extent, not perfectly smooth.
• The force in question acts at the contact surface and opposes relative motion.
• Other forces like centripetal, centrifugal, inertia and tension are present in different contexts.

Concept / Approach:

Friction is defined as the force that opposes the relative motion or tendency of such motion between two surfaces in contact. It acts tangentially along the surfaces and opposite to the direction of attempted motion. Centripetal force is the net force directed towards the centre that keeps a body moving in a circular path. Centrifugal force is a pseudo force observed in a rotating frame of reference. Inertia is not a force but a property of matter that resists changes in motion. Tension is the pulling force transmitted along a string or rope. Therefore, only friction matches the description of the force resisting sliding motion between surfaces.

Step-by-Step Solution:

Verification / Alternative check:

Imagine pushing a heavy box across a rough floor. When you apply a small push, the box may not move because friction balances your push up to a limiting value. If you increase the push beyond this limit, the box starts to slide, and a kinetic friction force continues to oppose motion. Throughout this process, the force that resists motion is friction. No centripetal or centrifugal forces are involved because there is no circular motion, and tension would only appear if the box were pulled by a rope.

Why Other Options Are Wrong:

Option A (centripetal force): This is the radial force that keeps an object in circular motion and does not directly describe surface resistance to sliding.

Option C (centrifugal force): This is a pseudo force experienced in a rotating frame of reference and is not a contact force between sliding surfaces.

Option D (inertia): Inertia is the tendency of a body to resist changes in its state of motion; it is not a force.

Option E (tension): Tension is the pulling force along a string, cable or rope and is not the resistive force between sliding surfaces.

Common Pitfalls:

Some students confuse friction with inertia because both resist motion in some way. It is important to remember that friction is an actual force that arises from microscopic irregularities and interactions at contact surfaces, while inertia is an inherent property of mass. Only friction appears as a force vector in free body diagrams when two surfaces are in contact and one tends to move relative to the other.

Final Answer:

The resisting force between sliding surfaces is called friction.