How accurate are friction coefficient tests for slippage?

Answer 1

One material may be placed on a movable ramp of the second material which is slowly elevated at one end until the first material slides. The coefficient is related to the angel. Every combination (except glue?) must slide before 45 degrees elevation. One problem is 'stiction' because the angle needed to start a slide may be greater than that to sustain it. Also the conditions (roughness) of the two materials may affect the result. A cog railway train can not ascend a mountain using friction alone. When the experiment is set up correctly and repeated many times, a coefficient of friction can be averaged to the accuracy required for the specific combination. BTW, steam shovels on crawlers used to be a real hazard on ice or snow because the great weight was spread out over a great surface area. You would not want to ride one down a hill.