Coefficient of friction on an inclined plane?

[Sharlyn]

Homework Statement

A lab I've performed was measured using forces. As the mass increases, the force does as well. The inclined plane is at an angle of 30 degrees. Now, finding the coefficient, should the kinetic and static friction be decreasing on a plane? I've measured the frictions on a flat surface but the coefficient increases on the surfaces.
For example: First )Mass = 0.25kg therefore ForceG =(0.25)(9.8)= 2.45
Force Applied = 1.5N
Coefficient = 0.71
Second Mass) 0.33975kg, ForceG=4.21
Force Applied = 2.0
Coefficient = 0.69

Homework Equations

μ = Force of Friction/Force Normal
Force Normal = -mg(cos30)
Force Friction = -Fapplied

The Attempt at a Solution

I used all the equations I was provided with, and first coefficient: 0.71, then 0.69, 0.68
I was told that when you're applying force on an inclined plane, the Force itself will increase. I'm having troubles understanding WHY the coefficient is going down especially since the mass is increasing.

 

[sa1988]

The coefficients you've got there look reasonably similar to me.

If you repeat the experiment many times with lots of different masses, you should end up with results all around the 0.70 mark.

 

[haruspex]

If the trend in the numbers is not just random error, it may be to do with the details of the set-up. You would need to post the details.