We've all heard of the saying that opposites attract and likes repel but did you know that this is actually what happens down at a microscopic level with electrical charges?
In 1785, Charles Coulomb set forth to investigate the unknown laws of electrical charge interactions. This would eventually lead him to formulate what is now a fundamental part of electromagnetism: Coulumb's Law of Electrostatics.
Coulomb discovered two relations in the measurement of the electrostatic force between charged particles. He found that the force is inversely proportional to the square of the distance between the two charges (r) and is directly proportional to the product of the two charges (q1 & q2). To formulate this into an equation, he went on to introduce a constant k (8.99 x 10^9 N m^2 C^-2) which does have a longer form as seen below. The funny-looking "e" with a zero beside it denotes the electric permittivity of a vacuum, which is just a fancy way of describing how easy an electric force can travel through a vacuum.