Test your understanding of Section 21.2. Consider two light metal spheres hanging on a nylon thread. One of the spheres has a net negative charge, while the other has no net charge. (a) When the spheres are close but not touching, do they (i) attract, (ii) repel, or (iii) exert no mutual force? (b) If the spheres touch, do they (i) attract, (ii) repel, or (iii) exert no mutual force?