名词

1. 钟摆
The pendulum of a clock is a rod with a weight at the end which swings from side to side in order to make the clock work.

2. （局势意见等的）摇摆不定，变化不定
You can use the idea of a pendulum and the way it swings regularly as a way of talking about regular changes in a situation or in people's opinions.

1. an apparatus consisting of an object mounted so that it swings freely under the influence of gravity