Question

Which of the following statements is true regarding static friction?

• A. It always equals the maximum static friction.
• B. It is always less than kinetic friction.
• C. It adjusts up to a maximum value to prevent motion.
• D. It acts only when the body is moving.

Hint:

Static friction prevents motion and adjusts its value to match the applied force up to a limit:
\[ f_s \leq \mu_s N \] It acts only when the body is at rest relative to the surface.

Answer 1

The Correct Option is C

Static friction is the force opposing the start of motion between two surfaces. Unlike kinetic friction, static friction adapts to the applied force.
Key property:
Static friction is self-adjusting, increasing with applied force until it reaches its maximum static friction, calculated as:
\[ f_{\text{max}} = \mu_s N \] where \( \mu_s \) is the coefficient of static friction and \( N \) is the normal force.
Analysis of options:
- (A) It always equals the maximum static friction: Incorrect. It equals the maximum only at the point of impending motion; otherwise, it is less.
- (B) It is always less than kinetic friction: Incorrect. Static friction is typically greater than kinetic friction.
- (C) It adjusts up to a maximum value to prevent motion: Correct. This is the fundamental characteristic of static friction.
- (D) It acts only when the body is moving: Incorrect. This describes kinetic friction.