1. The mass distribution: The further the mass is distributed from the axis of rotation, the larger the moment of inertia. This is why a solid disk has a higher moment of inertia than a thin ring of the same mass.
2. The axis of rotation: The moment of inertia changes depending on where the axis of rotation is located. For example, a rod has a different moment of inertia when rotated about its center than when rotated about one end.
Therefore, even for a fixed mass, the moment of inertia can change:
* Changing the shape or mass distribution: Imagine a figure skater spinning with arms outstretched. When they pull their arms in, they decrease the distance of the mass from the axis of rotation, leading to a decrease in moment of inertia. This allows them to spin faster.
* Changing the axis of rotation: A spinning top has a different moment of inertia depending on whether it's spinning around its main axis or wobbling around a different axis.
In summary, moment of inertia is not constant because it depends on the mass distribution and the axis of rotation. Any changes to these factors will result in a change in the moment of inertia.
