Conceptual friction problem

[k-rod AP 2010]

Homework Statement

Why are both types of friction dimensionless?

Homework Equations

The Attempt at a Solution

i said it was because the coefficients of friction are just ratios relating the normal force/frictional force of specific types of surfaces sliding past each other.

F=μ*F_n so μ=F_n in N/F in N so the Newtons cancel and leaves a dimensionless number

and the Frictional force F, is the force applied to resist motion, gained from μ*{F_n} where normal force is (mass*gravity)

would this be correct?

 

[issacnewton]

yes, $$\mu$$ is dimensionless since its a ratio of two forces

 

[k-rod AP 2010]

ok that's what I thought thanks for clearing that up