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Measurements of the charge produced by rolling or sliding contact between a metal or polymer sphere and a dielectric sheet have been carried out under controlled conditions. The dependence of charge on air pressure was studied. Charge decay and mobilities were estimated. The metal work-function had no effect on charge transfer. The polymer materials was of great importance, polar polymers charging positively with respect to both metals and non-polar polymers. The relation between charge per unit length and the square root of the normal contact force was found, and the time constant for charge transfer was evaluated.
Elsdon et al. (Sun,) studied this question.