There is a similar thought experiment I imagined to help me begin to understand the Bell's spaceship paradox: Consider two positively charged spheres, placed side-by-side inside a frame S' with a string stretched to the point where it balances the repulsive electrostatic force between them. For sake of simplicity, assume that the frame S' and the spheres are perfectly rigid and frictionless. One sphere is directly mounted to the frame S' and the other sphere is tied to the frame S' with a very thin thread same as in the Bell's paradox. The frame S' starts accelarating relative to the frame S. According to the frame S', everything is stational and the rope would stay intact. But according to frame S, there would be an attractive magnetic force between the spheres which would break the rope.