Measurements of the friction of various brake linings against polished iron have been made at speeds so low that surface temperature (known to be important at higher speeds) could be neglected. Samples had to be run in thoroughly immediately before testing to secure reproducible results. The coefficient of dynamic friction was lower than the static coefficient at the lowest speeds, increased markedly, and approached a constant value at the highest speeds studied (12.5 ipm). Other apparatus was used to extend the range to 800 fpm. When the surface temperature was held constant, the friction coefficient passed through a broad maximum and thereafter decreased slightly as the speed was increased. The transition from smooth sliding to stick-slip friction was studied as a function of speed and load. A critical speed was found, above which only smooth sliding was possible, regardless of load. The time-force traces obtained during stick-slip motion supply information about the static coefficient, and also the elastic properties of the brake lining.

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