I am a physics major taking freshman year physics courses. We did a lab experiment where we were given three objects and inclined plane, and we were asked to find the coefficients of kinetic and static friction for each object. The coefficient we found for static friction was greater than kinetic friction in each object. It was greater by about 0.05 in each object (e.g. mu_s = .22, mu_k = .29).
Our method to find the coefficient of kinetic friction was to measure the acceleration down the ramp using a vernier sensor, then solve using the mass and the angle, which was arbitrarily chosen to be 26.8 degrees.
Our method to find the coefficient static friction is not very precise. We used a pulley system to elevate the ramp until the object was just barely sliding, and we measured the incline at that point. Therefore, our coefficient of static friction is really only a best estimate.
As the saying goes, "it's a poor workman who blames his tools," or in this case his experimental method. But there is no special condition to make this situation predictable, and I can't find another explanation other than our "best estimate" method simply isn't accurate enough. Or is the 0.05 a negligible amount?
Any ideas?
The current draft of my lab report is posted here.
