The electrical force is a force billions of times stronger than gravity. Why is it, then, that we do not feel this huge force? The answer to this is that the electrical force both attracts and repels. Our universe is composed of an equal number of positively charged and negatively charged particles. The positive particles attract negative particles and repel other positive particles. Negative particles attract positive particles but repel other negative particles. Molecules are composed from these different particles, and the electric force usually cancels out almost completely.

Electric charge, the positive or negativeness of particles, is the quantity that underlies all electric phenomena. Atoms are composed of three differently charged particles. protons are positively charged and reside in the center, or nucleus, of an atom. Electrons are negatively charged and orbit the nucleus. Neutrons have no charge and are also found in the nucleus. So atoms have a positively charged interior and a negatively charged exterior. In most cases, atoms have as many protons as electrons and so have no net charge. However, atoms can lose or gain electrons. When this happens, the atom will have a positive or a negative charge. A charged atom is called an ion. Thus, an object can be charged by adding or removing electrons from it. If you rub a balloon through your hair, electrons from your hair rub off onto the balloon. The balloon becomes negatively charged and your hair becomes positively charged. The amount of charge depends on the amount of electrons. All charges have a magnitude equal to some whole number of electrons. An object cannot have a charge equal to a fraction of an electron, say, half of an electron. The charge of an electron is the smallest possible amount of charge. When an object is charged, no electrons are created or destroyed. The net force between the balloon and your hair before the charging is the same as the net charge after the charging. Like in momentum and energy, there is a conservation of charge.

The formula for electrical force looks almost exactly the same as the formula for gravitational force. Coulomb's Law, discovered by Charles Coulomb, states that electrical force between two objects is proportional to the product of the charges of the objects divided by the distance between them squared, or F~qQ/d². Add a constant, k, and the proportionality turns into the equation F=kqQ/d². The unit of electrical force is the coulomb (C), which is equal to about 6.25 billion electron charges. The numerical value of k is 9 billion Nm²/C². Note the large value of k, which shows that electrical force is much stronger than gravitational force.

Materials with electrons that are not firmly bonded to the nucleus transmit electrical current well. These materials are conductors. Materials with strongly bonded electrons do not allow electrical current to flow through them easily. They are insulators. Some materials are neither good conductors nor good insulators. These materials can be made to behave as either insulators or conductors, and are called semi-conductors. Materials with infinite conductivity, that is, materials with no resistance to electrical current, are called super conductors. Superconductivity occurs at very low temperatures (near absolute zero) and at very high temperatures.

Consider two metal balls with no net charge sitting near each other. If a positively charged bar is placed next to the balls, electrons will be attracted towards the bar. So the ball nearest the bar will be negatively charged, and the ball opposite the bar will be positively charged. If the balls are now separated, they will retain these new charges. The balls have been charged by induction.

When a single object is charged by induction, the electrons in the substance are rearranged so that one side of the substance is positive and one is negative. An atom or a substance with its electrons rearranged this way is said to be electrically polarized. Rub a balloon through your hair and it becomes charged. Hold the balloon next to a wall, and the wall becomes polarized. Let go of the balloon, and it sticks to the wall. This is because the part of the wall closest to the balloon is positively charged, and so by coulomb's law it attracts the balloon more than the opposite, negatively charged part of the wall repels the balloon.

Just as any object produces a gravitational field that extends indefinitely into space, a charged object produces an electric field that extends indefinitely into space. The strength of the field at any point is equal to the force felt by an object at that point divided by the charge of the object, or E=F/q. An electric field can be diagrammed by a series of lines emanating from or pointing towards a charged particle. The lines represent the direction of the field. Where the lines are close together, the field is strong, and where the lines are far apart, the field is weak. We always draw the lines as emanating from a positive particle and pointing towards a negative particle.

An electric field can be shielded. Air shields electric fields, making charges in air weaker than they would be in a vacuum. Metal can shield an electric field entirely. So inside a metal object, the electrical charge is always zero when no current is flowing through it. Therefore, in a metal object the arrangement of the charges on the surface of the object must be arranged in such a way that no particle inside the substance feels an electric force. In a sphere, the charges are positioned uniformly around the sphere. In other shapes, the positions of the charges are not uniform. Note that this only holds true when no current is flowing through the metal.

A charged object has electrical potential energy because of its location in an electric field. Consider a large negatively charged ball and a smaller positively charged ball. The small ball will be attracted to the large ball. If we take the small ball and pull it away from the large ball, we are performing work on it, giving it potential energy. If we release the small ball, it will accelerate towards the larger ball. If we give the small ball twice as much charge, it will accelerate towards the large ball twice as quickly.

Rather than dealing with the actual electrical potential energy of a particle, we like to consider the amount of potential energy per nit of charge. This is called the electric potential of an object. Our particle with twice as much charge had two times as much potential energy as the original, but the same electric potential. Electric potential=electric potential energy/charge, and two times the energy/two times the charge=energy/charge. The unit of measurement for electric potential is the volt. One volt is equal to one joule divided by one coulomb. The upshot of all this is that each point in an electric field has a single electric potential, regardless of the charge of a particle at that point.

Electrical energy can be stored in a device called a capacitor. A simple capacitor is composed of two metal plates separated by a small distance. The two plates are then charged, usually by a battery. The charged plates store electric energy equal to the electric potential difference between the positive and negative battery terminals. A capacitor is discharged when a conducting path is provided between the two plates.