I am trying to workout the drift of a charged particle from another particle using coulomb law. but the problem is the further the particles move, the less the force between them, so how can I work out the drift in such case? We know that the force between two charged particles is: F = (k Q1 Q2)/r^2 where k is coulomb constant and r is the distance between the particles. I can find the drift using Newton motion laws, by working out the acceleration (a) from the force (F = ma) m is the mass, and then using drift = (a.t^2)/2 + V0.t + x0 (assume v0 = 0 and x0 = 0). You see the problem, the further the particles get the smaller the acceleration, and the smaller the drift, so how to treat this properly please?