The electric charges generated by rubbing are static electric charges. These electric charges remain bound on the surface of the charged object. When a glass rod is rubbed with silk, some of the electrons from the glass atoms are transferred to silk. Due to the deficiency of electrons in the glass atoms, it becomes positively charged. Whereas the silk has acquired electrons, it becomes negatively charged. Iron rod is a conductor. As soon as we charge an iron rod by rubbing with another material, the electric charge flow through our hand and body and flows into the earth. As a result, the iron rod remains un-charged by rubbing, if held by hand.