# Coefficient of friction-someone help me, please!

1. Dec 1, 2005

### Inka

Im not sure this is in the right place, I suppose it could be under maths or physics, but this seems more appropriate as it's a physics experiment. Anyway, I'm trying to determine the coefficient of kinetic friction for various surfaces by sliding an aluminium block down these varying surfaces and recording the distance, time and velocity and so on. Im also doing this same procedure but increasing the mass of the block, and I was wondering whether this should have any effect upon the coefficient of the surface or if the coefficient should stay constant regardless of increased mass. Any help would be GREATLY appreciated, I'm going nuts here because half the data I've gathered seems to make no sense (logical considering the crappy equipment I had to work with) and I don't know what I'm supposed to be seeing!

Thanks

2. Dec 1, 2005

### El Hombre Invisible

The coefficient should remain the same irrespective of the mass of the block. However, a heavier block will yield a larger normal reaction by the surface. This normal reaction will lead to an increased friction force, since

$$F_{fric} = \mu_{slide}N$$

where $$\mu_{slide}$$ is the coefficient of kinetic friction and N is the normal reaction (N = -mg for a horizontal surface).

3. Dec 1, 2005

### brewnog

Don't be too perturbed. As far as they go, the coefficient of friction model is pretty piss poor at accurately describing a real life friction scenario. Stick with it, just don't expect real life to repeat the theory too closely.