Static friction — identify the correct set of properties for the limiting static friction between two contacting surfaces.\nChoose the most comprehensive statement.

Topic: Friction — properties of static (limiting) friction

Given data

• We are asked which statements about static friction are correct.

Concept / Approach
Limiting static friction F_s,max ≈ μ_sN (proportional to normal reaction). It depends weakly on apparent area because true microscopic contact area scales with load and roughness, not geometric area. The direction of static friction is always opposite to the impending motion (the tendency to move).

Step-by-step reasoning
1) Constant ratio: F_s,max / N = μ_s ⇒ proportional to N.2) Independence from apparent area: friction depends on real area of contact (asperities), not just the visible area.3) Direction: acts opposite to the tendency of motion to prevent slipping.

Verification
These are standard results in classical mechanics and tribology for dry Coulomb friction models.

Common pitfalls

• Confusing static with kinetic friction behavior.
• Thinking friction always equals μN; for static friction it is ≤ μ_sN up to the limiting value.

Final Answer
All of the above