A tortoise on a skateboard travelling in a straight line at constant velocity carries two negative
electric charges on its back. As far as the tortoise is concerned, the charges are stationary, and
the repulsive force between them is given by Coulomb's Law.
However, as far as a sparrow perched on top of a tree, observing the tortoise from a distance is concerned,
the charges are moving. The sparrow knows that when two parallel current-carrying wires are placed next to
each other, they are attracted to each other by a magnetic force. The charges that the tortoise is carrying
are moving like the charges in the parallel wires. Therefore, the sparrow sees not only the Coulomb repulsion,
but an extra magnetic attractive force.