When two objects are electrically charged, they exert a force on each other. If the objects have like charges, they repel; if they have opposite charges, they attract. The child above has become negatively charged after his ride down the slide. Since each of his individual strands of hair is negatively charged, they repel each other. The force of the attraction or repulsion between charges can be calculated using Coulomb’s law. On some occasions, however, it is difficult to identify and/or quantify one of the charges involved. To work with such a situation, physicists consider what is called an electric field. These fields exist in the area around charged particles and exert forces on all charges within the field. By using the field for calculations, we need not know anything about the charge itself.