There four types of forces in the universe: gravitational, electromagnetic (it has been shown that electric and magnetic force are actually the same) and 2 types of nuclear forces.











Electricity (Intro)


Charging by contact or friction and charging by induction

Electrodynamics: Electric current

Electric energy

Difference between static electricity and "normal" (or current) electricity

The gold leaf electroscope

Electricity Quiz


Conductor-material in which charges can move easily

Insulator- materials in which charges can hardly move





The gravitational force acts on every single particle on the universe, because all particles have mass. The electric force, however, only acts on particles that have a property called charge!

There are two types of charges: positive and negative.

The opposites attract each other and the likes repel.

Because of this balance between repulsions and attractions, the universe can be stable. If all electric interactions were repulsive the universe would disintegrate, because the electric force is stronger than the gravitational force. The nuclear forces have short range and are not involved in the formation of macroscopic matter. They only act within the nucleus of the atom.

If something has equal numbers of positive and negative particles, the overall result will be a neutral state.

For example, all the atoms (look at periodic table) are neutral, although they are made of positive and negative particles: the electron is negative, the proton is positive and the neutron is neutral. That happens because the number of protons is always equals the number of electrons, and the charge of the electron equals minus the charge of the proton.

If the atom gains electrons it becomes negatively charged and if it loses them it becomes positively charged (it is very difficult to remove or add protons - this constitute a nuclear reaction- chemistry only deals with movement of electrons). A charged atom is called an ion.

Charge, like energy, cannot be created or destroyed. When you charge something* up we are simply transferring charges from one place to another.

*when you charge a battery, for instance on your mobile phone, you are not adding new charges to the battery. You are simply rearranging the charges already inside the battery.

How to charge something?