where r 12 = r 1 − − r 2 is the displacement vector between the charges, r ^ ^ 12 = d e f r 12 | r 12 | a unit vector pointing from q 2 to q 1 , and ε ε 0 the electric constant. Here, r ^ ^ 12 is used for the vector notation. The electrostatic force F 2 experienced by q 2 , according to Newton's third law, is F 2 = − − F 1 .