pendulum
noun uk/ˈpen.dʒəl.əm/ us/ˈpen.dʒəl.əm/
[ C ]摆，摆锤;（尤指）钟摆
a device consisting of a weight on a stick or thread that moves from one side to the other, especially one that forms a part of some types of clocks
The pendulum in the grandfather clock swung back and forth. 落地钟的钟摆来回摆动。
The spaceship's jets were fired periodically to dampen a side-to-side pendulum motion that had developed. 宇宙飞船的喷射装置周期性地喷射，以减缓飞船出现的左右摇摆现象。
[ S ]摇摆不定的事态（或局面）;（尤指）观点的摇摆不定
a change, especially from one opinion to an opposite one
As so often in education, the pendulum has swung back to the other extreme and testing is popular again. 人们的观点又回到了另一个极端，考试又流行起来了，这种摇摆不定的现象在教育领域经常出现。