Question

Which of the following is true about the coefficient of static friction \((\mu_s)\) and the coefficient of kinetic friction \((\mu_k)\)?

• A. \(\mu_s\) is always equal to \(\mu_k\)
• B. \(\mu_s\) is always greater than \(\mu_k\)
• C. \(\mu_s\) is always less than \(\mu_k\)
• D. Depending upon applications, \(\mu_s\) can be greater, less or equal to \(\mu_k\)

Hint:

Always remember: \[ \mu_s\gt \mu_k. \] It is generally harder to start the motion of an object than to keep it moving, which is why the coefficient of static friction is greater than the coefficient of kinetic friction.

Answer 1

The Correct Option is B

Step 1: Recall friction concepts.
Static friction acts before motion starts and can adjust up to a maximum value \( \mu_s N \). Kinetic friction acts during sliding and equals \( \mu_k N \).

Step 2: Compare coefficients.
Experiments show that the maximum static friction force exceeds kinetic friction force for the same normal force, so \( \mu_s > \mu_k \) always.

\[ \boxed{\mu_s > \mu_k\text{ always}} \]