Electric Charge and Coulomb’s Law

Electric charge is a fundamental property of matter.
Electrons carry a charge of negative one “electron unit”, and
protons a charge of positive one “electron unit”.
Electric charge is conserved in a closed system.

The SI unit for electric charge is the Coulomb:

            about 6.25 x 10^18  electrons    add up to 1 Coulomb

The Coulomb is a very LARGE amount of charge — ordinary
situations contain a tiny fraction of a Coulomb.
If one Coulomb per second moves past a fixed point in a wire,
that wire is carrying a current of one Ampere.
Conductors allow charge to move freely through them.
Metals are good conductors.
Insulators keep charged particles nearly fixed in place.
Glass, rubber and plastic are good insulators.

Coulomb’s Law describes the force between two charged point-like
particles:

                            q1 * q2
                F   =  k * ----------
                              r^2

where

               k    =  Coulomb's constant = 8.99 x 10^9    (N*m^2/C^2)
               q1   =  charge on first particle            (Coulombs)
               q2   =  charge on second particle           (Coulombs)
                r   =  distance between particles          (meters)

If the result is positive, the force is repulsive.
If the result is negative, the force is attractive.