Let's imagine a stretched spring with a negative Q charge at each end. At equilibrium, the repulsive electrostatic force and the force exerted by the spring on the charges cancel each other. If we increase or decrease one of the charges, the length L of the spring will change, and this will make a bell ring. Now I suddenly run in a direction perpendicular to the spring. In my reference frame, a tiny attractive magnetic force will appear. The spring will shorten and the bell will ring. Is this correct ? I know similar questions on the relativistic effect etc. have been posted, and I have read many, but it seems to me none answers my question.