Hi all i am really confused about this, why does a thin cylindrical shell has the same moment of inertia of a hoop? i understand the I for a thin hoop is mr(square), and i know how to do this. but i just get confused why a cylindrical shell has the same result? and i dont know how to show the work. i asked my physics teacher but he didnt explain very clearly. Moderation note: Duplicate threads merged since both threads had been answered.