I don't have the ability to make the experiment to answer these questions :

Let $A$ and $B$ be two materials. Is the static coefficient of friction of $A$ on $B$ equal to the static coefficient of friction of $B$ on $A$ ? I ask the same question for the sliding coefficient of friction.

Thank you in advance for any help you can provide.

  • 2
    $\begingroup$ It seems like it should have the same value. Changing which object is sliding is equivalent to changing your frame of reference from being attached to the "fixed" object (lab frame) to being attached to the "moving" object. Since everything has to be behave properly under a change of frame, the friction coefficient should be the same. $\endgroup$ Jul 2, 2015 at 19:18
  • $\begingroup$ That being said, sliding (eg.) a milled steel block on a cold-rolled aluminum surface is NOT the same as sliding a milled aluminum block on a rolled steel surface. The surface finishes will be different, so the friction can very well be different. $\endgroup$ Jul 2, 2015 at 19:19

1 Answer 1


They are the same.

If the force that A put on B were different than the force that B put on A, then the system would be in violation of Newton's third law.

The friction equation tells us that $F_F=\mu*F_N$.

$F_N$ is the normal force, or the force that each of the materials applies on each other.

Because the frictional forces must be the same, and the normal forces must be the same, then the coefficient of friction is, by definition, the same.


Your Answer

By clicking “Post Your Answer”, you agree to our terms of service and acknowledge you have read our privacy policy.

Not the answer you're looking for? Browse other questions tagged or ask your own question.