Friction is the resistance to sliding between 2 surfaces in contact when pressed together. Friction is often described with a single coefficient which is the sliding resistance force divided by the normal force pushing the 2 surfaces together. In general, friction can be a function of the materials that make up the surfaces, the normal pressure, temperature and the rate of sliding.
There are a few experiments that are particularly useful in characterizing friction. The experiments are outlined below.
Typical Plastic Experiments:
A friction sled test is used for low normal force and comparative tests.
A more elaborate axial torsion friction test is used for higher normal force tests.