Complex sentence: Because rotational inertia is a part of angular momentum, it necessarily includes all of the complications of moment of inertia, which is calculated by multiplying elementary bits of the mass by the squares of their distances from the center of rotation.
Split into simpler sentences: Because rotational inertia is a part of angular momentum, it necessarily includes all of the complications of moment of inertia. This is calculated by multiplying elementary bits of the mass by the squares of their distance from the center of rotation.