Inertia is the property of an object to resist a change in its motion.
For linear motion the inertia is directly proportional to the mass of the object.
e.g. It is much more difficult to start/stop/change the motion of a 10 kg ball than a 1 kg ball of the same size. . . so more mass = greater inertia!
Rotational Inertia (I) measures the same property to resist change of motion for rotating objects
BUT for rotating objects there is another factor involved other than just the mass . . . The distribution of the mass on the object in relation to the axis of rotation also affects how quickly the motion will change.
This video shows how two cylinders, with identical dimensions and mass will accelerate at different rates down a slope because the mass is distributed differently.
One cylinder has more of the mass further from the axis of rotation.
Will it have more or less rotational inertia then the other and what are the consequences?