There's a force F between oppositely charged parallel plates. If the plates are free to move, they accelerate towards each other with acceleration a. If the plates are large and close to each other, we can reduce the mass of the system by moving the plates closer to each other, while keeping the force between the plates unchanged. Does this mass reduction operation result in increased acceleration of plates when the plates are let free? If the acceleration of a plate is indeed increased, can we then conclude that the mass of that plate was decreased?