The study of the effects of static charges. These charges are produced by too many or too few electrons. Electrons, in turn, are the most movable charge forms, and are found spread around the positive charge in the nucleus of the atom. If there are too few electrons, a positive charge will appear. If there are too many, a negative charge will appear. If the charges are in balance, then no charge is detected. The electron is a fundamental particle, and has interesting characteristics, besides the charge, it spins, and this spin gives rise to a magnetic field, much like an electric motor.
The decision to call some charges positive and others negative was arbitrary. This gives rise to a potential misunderstanding when charges are moving in a circuit. This will be deferred to a later section, on electricity.
The fundamental study of these charges in isolation can best be observed by experiment. If we generate a charge by friction, say fur on hard rubber, or silk on glass, we can transfer the charge to a small ball coated with aluminum foil. This ball is held up by a thin thread. Nylon or silk work well.
If however the air is damp, the charge will leak off the metal balls.
Two such balls, charged by the same static source will repel each other. If we use two different sources, they will attract each other. Maybe.
We can measure the amount of attraction or repulsion by a simple means. If we measure the weight of these balls, then we know that they are attracted by the earth. Other forces on these balls will cause them to swing away from hanging straight down.
By measuring the movement, or the angle, we can figure out what tiny force is pushing the ball away from the vertical. The tangent function is the perfect candidate to resolve this problem. ((add more text and diagrams here))
It would be nice to find out what happens when some charge is removed. It turns out, that if we use a third ball, of the same size as the other two, we can exactly halve the charge.
From this we can see that we can measure the effects of increasing distance, and decreasing charge.