¹⁷A common analogy for this is two children swinging on adjacent swings in a playground. Imagine the distance between the children being the amount of voltage difference between the two generators at any given point in time, with the amplitude of each child’s swing representing the peak voltage of each generator and the pace of each child’s oscillation being the frequency of each generator. When two children are swinging in perfect synchronization, the distance between them remains minimal at all times. When they swing 180^o out of phase each other, the distance between them varies from minimal to maximal at a pace equal to the difference in their individual swinging rates.