Arrange the charges as shown in the figure. F 2 and F 3 have the same magnitude. Charge cannot be created or destroyed, but charge can be separated. In atoms, the outermost electrons are bound to the nucleus by the weakest force. They have the largest distance from the nucleus, and they are also repelled by the inner electrons.
Some atoms attract their outermost electrons more strongly than other atoms.
For example, atoms in rubber attract their outermost electrons more strongly than atoms in wool. When a rubber rod is rubbed with wool, electrons near the surface are attracted more strongly to the rubber than to the wool, and some electrons are transferred from the wool to the rubber. The rubber becomes negatively charged and the wool becomes positively charged. When enough electrons have been transferred, then the wool becomes more attractive and the rubber more repulsive to additional electrons, and the transfer stops. This phenomenon is called triboelectricity or contact electricity .