  Despite its simple manifestation, triboelectric charging is believed to be
unthinkably complex because of the unresolvable interfacial interaction between
two rubbing materials. Here, we for the first time reveal a simple physics of
triboelectric charging and the origin of triboelectric series based on the
causality of friction-originated thermoelectric charging effects at the
interface, characterized by the density (\rho), specific heat (c), thermal
conductivity (k), and Seebeck coefficient (S) of each material. We demonstrate
that energy dissipational heat at the interface induces temperature variations
in the materials and thus develops electrostatic potentials that will initiate
thermoelectric charging across the interface. We discovered that the trends and
quantities of triboelectric charging for various polymers, metals,
semiconductors, and even lightning clouds are simply governed by the
triboelectric factor, S/\sqrt{{\rho}ck}. Our findings will bring significant
new opportunities for understanding and management of static electrification.
