Electric charge is a property of matter. It occurs in positive and negative forms. One unit of charge is e. A proton has a charge of +e and an electron has a charge of −e. Charge, represented by q, is measured in coulombs (C). The elementary charge e equals 1.602 18×10⁻¹⁹ C.

An ordinary object is charged when it has an imbalance of protons and electrons.

Charge is always conserved. Though charges may be transferred from object to object, charge cannot be created or destroyed, and the net charge of an isolated system will remain the same.

Electrons flow more freely in some objects than in others. Conductors allow electrons to move relatively easily, while insulators do not. A ground can drain away any excess charge from a conducting object. The most common ground is literally the ground: Earth.

Charged particles exert an electrostatic force on each other. Unlike gravity, which is always attractive, the electrostatic force can be either attractive or repulsive. Opposite charges attract each other, while like charges repel.

Coulomb’s Law describes the amount of the electrostatic force between two point charges. It is proportional to the product of the charges’ magnitudes and inversely proportional to the square of the distance between them.