In recent years, the classic term “moment of inertia” has started to be largely retired in favor of the more descriptive “rotational inertia;” likely a good choice, as “moment” has long since ceased to have any non-time-related usage in everyday English. But call it what you will, it can be a challenging concept for beginning students to wrap their heads around.
Demonstration D2-01: Ring and Disc on Inclined Plane is a useful illustration for clarifying this concept. Two objects of similar mass and radius, a metal ring and a solid wooden disc, are placed on an inclined plane with no initial velocity. As they are accelerated by gravity, the disc quickly outpaces the ring. You can invite students to make a prediction ahead of time about their behaviour, presenting it as a race between the two objects, and invite them to discuss the results afterwards.
