pendulum

Definition

A weight hung from a fixed point so that it can swing freely, especially a rod with a weight at the end that regulates a clockwork mechanism.

中文 从固定点悬挂的重物，能够自由摆动，特别是用于调节钟表机制的带有末端重物的杆。

Example

"The pendulum swung slowly back and forth in the grandfather clock."