The column slow equation gives the magnitude of the force that QA exerts on a QB, and also the magnitude of the force that can be exerts on a QA. These magnitude are equal.You can observe this example of newtons third law of motion when you bring two stripes of tape with like chart together, each exerts of force on the other, if you bring charged come near, either striped the stripe with its small mass moves readily The aeration of the is less because of its much greater mass the electrostatic force like all force is a vector quantity force victors have both magnitude and direction.The coulombs slow equation gives only the magnitude of the force to determine direction you can draw a diagram, using force vectors .