# Effect of velocity upon kinetic friction

This question has been asked before...

...but there's a very specific part I'm struggling with, and it's not addressed in that post.

Part of what causes friction is the breaking of microscopic ridges in the materials sliding on each other, protrusions that catch and need to be dislodged.

Let's say it takes a certain amount of force to break each of these ridges.

If the two surfaces are moving faster relative to each other, they would need to dislodge more of these protrusions in the same amount of time. It seems to me, then, that kinetic friction (at least between rough surfaces) should be velocity dependent. However, the standard explanations say it isn't.

Why?

Thank you!

• The original reason I asked this question was because a problem in my physics book (Halliday Resnick Kline) asked us to find the acceleration of a slipping wheel, and the supposed realization was that it doesn't matter what the wheel's current angular velocity is if it's slipping, all that matters is the normal force and the coefficient of kinetic friction. Dec 28, 2018 at 20:49