A Modern but Simple Approach to Teaching Friction

We present an experiment for measuring friction, using interleaved sheets of paper.Our results support the modern theory that friction is dependent on surface contact area (A).Also, our results support the classical theory of friction being proportional to the normal force (N), but this is only true over a limited range of N, where the "effective" area of contact increases in a manner proportional to N. Outside of this range, friction varies nonlinearly with N but linearly with A. Suggestions are made for extending the function of this experiment to measure the friction of other materials.Also, we present techniques to limit the nonlinear behavior of N and to eliminate several key sources of experimental error.