A spherical modular self-reconfigurable robot allows modules to connect at any point on its spherical surface, and the modules can continuously roll relative to each other after the attaching. Rolling contact motions have been formed among the spherical modules, which has the potential of the absence of abrasion wear and the enlargement of reachable configurations. This paper describes the kinematic behaviors between two adjacent modules as a spherical rolling contact joint, and establishes the relationship between the relative motion rate of the modules and the joint angular velocity. The dynamic equations between the spherical modules are derived as a special case of spherical modules moving on a general surface. By combining the derived motion equations among spherical modules with the variable topology description of the spherical modular self-reconfigurable robot, the unified motion equations for various configurations of the robot can be obtained.