The tangential force acting on an object that opposes it from sliding freely on the adjacent surface is called

Analyze the question The question asks for the name of the force that acts tangentially (parallel to the surface) and opposes an object sliding on an adjacent surface.

Explain the concept When two surfaces are in contact, two kinds of contact force can act:

• Normal reaction: acts perpendicular to the surface.
• Friction: acts parallel (tangential) to the surface and opposes relative motion or the tendency to move.

Friction arises from the roughness of the surfaces and the molecular attraction between them. Its limiting value is F = μR, where μ is the coefficient of friction and R is the normal reaction.

Solution: checking each option

• A. Normal force: acts perpendicular to the surface, not tangentially. ❌
• B. Friction force: acts along the surface and opposes sliding. ✅
• C. Weight: the gravitational pull on the object, directed downward toward the Earth's centre. It is not a surface-contact force. ❌
• D. Upthrust: the upward force a fluid exerts on a body immersed in it. ❌

Answer: B. Friction force

Tip: Remember "Friction is Fighting the slide." Normal is Never along the surface, because it is always perpendicular (normal means 90°). When a question says "tangential" and "opposes motion," think friction right away.