Contact electrification occurs in many granular material systems due to particle-particle and particle-wall contacts.In this paper,we used a simple device to characterize the electrification of different spheres in a rotating spherical container.The charge of the spheres was quantified by a Faraday cup after rotating for various time and the disperse behaviors of charged spheres were recorded by a camera.The effects of the rotational time,sphere size,rotational speed,sphere material,and relative humidity on the equilibrium charge and triboelectric coefficient were analyzed.The results show that the equilibrium surface charge density is independent of the sphere size and the rotating speed,whereas the larger rotating speed enhances the triboelectric coefficient.It is also shown that charge relaxation constants are two orders of magnitude lower than the charge generation constants for all spheres at a low relative humidity.The increase of water molecules in the air was found to result in the decline of charge generation constant and the rise of charge relaxation constant,which together cause the decrease of the equilibrium surface charge density.