One of the most important discoveries about charge is the law of conservation of charge: Charge is neither created nor destroyed. Charge can be transferred from one object to another as electrons and ions move about, but the total amount of charge remains constant. For example, charging a plastic rod by rubbing it with wool transfers electrons from the wool to the plastic as the molecular bonds break. The wool is left with a positive charge equal in magnitude but opposite in sign to the negative charge of the rod: . The net charge remains zero.
Diagrams are going to be an important tool for understanding and explaining charges and the forces on charged objects. As you begin to use diagrams, it will be important to make explicit use of charge conservation. The net number of plusses and minuses drawn on your diagrams should not change as you show them moving around.