So I was reading my textbook and it says that we are given a situation where two particles of the same charge are separated by the distance 0.0200m. Another particle of the opposite charge is then placed in between the other two particles, 3/4 the distance mentioned away from one and thus 1/4 away from the other (assuming the radii to be negligible). The book goes on to say that placing this third particle in between the other two does not disrupt the force between these other two particles. This is where I became confused because this would seem to violate the law of conservation of energy. If the force between the original two particles goes unchanged when the third particle is added and yet the two original particles, must also exert another new force on this new particle, where does this extra energy for the extra force needed come from. I would think that the force between the two original particles would have to be reduced in order to be able to have some energy left for the force with the new particle. Whats wrong with my thinking?