Answer: Nature and roughness of surfaces.
- A Speed of motion in typical laboratory settings
- B Size of contact area under usual circumstances
- C Nature and roughness of surfaces
- D Weight of the object according to most researchers
Correct answer: C. Nature and roughness of surfaces
Explanation: Coefficient of friction is a property of the materials and their surface texture, not area or speed.
Free-body diagram of a block on an incline: weight (mg) resolves into mg sinθ along the slope and mg cosθ into the slope, balanced by the normal force N and friction f.
Concept context
Newton's three laws, friction, circular motion, and free body diagrams.