in what situations would you require the use of the parallel axis theorem? Also, from the physics book it says that let x and y coordinates of P(a point parallel to the first axis) be a and b. then let dm be a mass element(what does this mean? a point anywhere within the object?) with the general coordinates x and y. the rotational inertia of the body about the axis through P is then I=∫r^2 dm = ∫[(x-a)^2 + (y-b)^2]dm im a little confused and any clarification would as to how, why, and when this would make sense. thanks!