Parallel Axis Theorem
Suppose we want to find the rotational inertia I of a body of mass M about a given axis. In principle, we can always find I with the integration. However, there is a shortcut if we happen to already know the rotational inertia loom of the body about a parallel axis that extends through the body’s center of mass.
This equation is known as the parallel-axis theorem. We shall now prove it and then put it to use in Checkpoint.