Final answer:
The video uses a pencil to demonstrate internal waves by attaching it to a rotating turntable and tracing its motion on paper, showing uniform circular motion.
Step-by-step explanation:
The common office item used in the video to demonstrate internal waves is a pencil. An internal wave can be modeled by attaching a dowel rod to a turntable and a pencil to the dowel. As the turntable rotates, the pencil will trace a wave pattern on a paper passed beneath it, effectively capturing its motion as a wave. This demonstration helps to illustrate the concept of uniform circular motion and its relationship to wave generation in a visual and tangible manner. Other related concepts include magnetism, where rubbing a paper clip with a magnet can induce magnetization, and matter categorization by a chemist, which includes substances such as coffee.