Coulomb's Law

"like (+)(+)" charges repel each other & "opposite (-)(-)" charges attract". This means there is a force between the charged objects. Coulomb's Law is what we use to find the magnitude and direction of the said force.

F = k*[(q1*q2)/(r^2)]

k ≈ 9 * 10^9 (N*m^2)/(C^2)

F (also) = [1/(4piε0)] * [(q1*q2)/(r^2)],

where k = 1/(4piε0)

The constant is called the permittivity of free space and has the value of 8.85 & 10^-12 (C^2)/(N*m^2)

This law is really a vector equation. We know this because force is a vector.

In addition, if there are multiple charges around (or multiple sources of force), the forces are vector additive through superposition. In general, this electric force is no different than other forces we have seen in the past.

In this figure, there are 4 identical charges that have an index number.

The force that q1 feels from q2 (call if F12) is repulsive. Charge q1 will have a similar repulsive forces from q3 and q4. Each of these forces will have a different magnitude because of the different distances between charges.

The total force on q1 (call it F1) is the superposition of all the individual forces.