The document discusses parallel axis theorem and radius of gyration. It states that parallel axis theorem can be used to calculate the moment of inertia about any parallel axis through the centroidal axis using a formula that considers the first moment of area and distance between the two axes. Radius of gyration is defined as the root mean square distance of particles from the axis of rotation and represents the equivalent radius of a rotating body. Rotational energy is the kinetic energy due to an object's rotation and is part of its total kinetic energy, calculated as the torque times the angular velocity of a rotating body.