ABSTRACT
The work of J. J. Thompson, Daniel Rutheford, and Neils Bohr proved that atoms were complex structures that contained both positive and negative particles. Investigations also showed that the normal atom is electrically neutral. Free electrons can travel through matter or remain at rest on a surface Electrons can be removed from a surface by means of friction, heat, light, or a chemical reaction. In this case the surface becomes positively charged. Friction causes loosely-held electrons to be transferred from one surface to the other. This results in a net negative charge on the surface that has gained electrons, and a net positive charge on the surface that has lost electrons. Objects with opposite charges attract, that is, they exert a force upon each other that pulls them together. Electrical charge flows freely in certain materials, called conductors, but not in others, called insulators.
