Coefficient of Kinetic Friction and Variables

[TyroneTheDino]

Homework Statement

This is a theoretical question from my homework. We did a lab in class where we were using motion to see how kinetic friction is affected by different variables. We found the acceleration of a sliding wooden block (sliding on another wooded block), and then used that acceleration with gravity to find what the coefficient of kinetic friction is.

The variable that we changed were the surface area of the block, the weight of the block, the amount of force pulling the block, and the material of the block. Which of these actually will affect the coefficient of friction.

Homework Equations

F_fk=μ_k*F_normal

The Attempt at a Solution

I am saying that the only thing affecting the coefficient is the type of surfaces involved in the motion. When we gave the wooden block a rougher surface it seemed that the coefficient went up dramatically. I am thinking that weight and area of the block have nothing to do the coefficient, and it is all dependent on the material...Thoughts on this?

 

[berkeman]

Homework Statement

This is a theoretical question from my homework. We did a lab in class where we were using motion to see how kinetic friction is affected by different variables. We found the acceleration of a sliding wooden block (sliding on another wooded block), and then used that acceleration with gravity to find what the coefficient of kinetic friction is.

The variable that we changed were the surface area of the block, the weight of the block, the amount of force pulling the block, and the material of the block. Which of these actually will affect the coefficient of friction.

Homework Equations

F_fk=μ_k*F_normal

The Attempt at a Solution

I am saying that the only thing affecting the coefficient is the type of surfaces involved in the motion. When we gave the wooden block a rougher surface it seemed that the coefficient went up dramatically. I am thinking that weight and area of the block have nothing to do the coefficient, and it is all dependent on the material...Thoughts on this?

That sounds good. The only caveat would be if the surface that the block was sliding on was deformable -- then the weight versus surface area of the block could affect the coefficient of friction. Can you give a couple examples of deformable surfaces where this would be true?

 

[DEvens]

You need a good explanation for your reasoning.

Maybe start with the idea of stacking one block on another. This doubles the Fnormal, but presumably also doubles the Ffk.

Then consider two identical blocks beside each other. This doubles the area, and also the Fnormal and Ffk.