What are some tips for improving a friction experiment?

[Vixus]

I started working on my project for real at school today and I have no idea if it really is a good project. It seems very arbitrary and messy somehow. I've got two experiments to explore friction.

Ff = Frictional force.
Fg = Component of force acting down parallel to incline
Fn = Reaction force perpendicular to plane.

Experiment 1 : An inclined plane with a block.
http://hyperphysics.phy-astr.gsu.edu/hbase/frict2.html#plo

- Change mass of block then incline plank of wood until block is on brink of sliding down. At this point I assume Ff is approximately Fg.
- Measure this angle.
- I worked out the coefficient could be found through tan [theta].
- So I intend to prove(/disprove) that the coefficient of static friction is NOT proportional to mass of the block on an inclined plane.
- I will also change materials the block surface is made of to make sure coefficient values correspond within materials.
- Results: Plot graph of Fg against Fn. Gradient = coefficient of s.f. Find error in gradient.

Experiment 2 : Horizontal plane with block pulled by mass.
- Just a backup to prove the coefficient values for each material/mass.
- Same method pretty much.

Problems
- There's no repeatability in this experiment really. I can't take multiple readings with a certain mass because there is nothing to read except the angle! There's no measuring equipment involved except a protractor :D. Everything else are calculated values.
- It seems to simple and I don't know if it will produce a great mark.

Help!
My teacher says to stick with it as it's how you write up the investigation and not the actual results that matters. But he said if it gets too out of hand and annoying I can think about switching to another one.
Now I must admit my school is a bit short of kit, the supplies are really crap. So if I had to switch to a different experiment what would you suggest? I don't want to do anything with pendulums particularly as it was already done last year. Are there any interesting experiments to do with electromagnetism that bear good results?

If I want to switch I better decide now, as I've already started writing this investigation up in my day book etc. Haven't taken any results yet.
Has anyone else done a friction experiment before? How can I improve mine? Tips, please!

 

[kuruman]

The coefficient of static friction depends on the materials that are in contact not on their mass. You can prove that by putting a box on the incline. Find the angle at which the box starts slipping. Then increase the mass of the box gradually by add ing something like marbles, gravel, beans whatever in incremental amounts. Plot angle vs. mass and see what you get. Change to a box of different material or change the material of the incline. Repeat. Compare coefficients of static friction and rank them.

Edited to correct typos.