What is parallel an perpendicular axis theorem?

Perpendicular axis theorem In physics, the perpendicular axis theorem (or plane figure theorem) can be used to determine the moment of inertia of a rigid object that lies entirely within a plane, about an axis perpendicular to the plane, given the moments of inertia of the object about twoperpendicular axes lying within the plane. The axes must all pass through a single point in the plane. Define perpendicular axes , , and (which meet at origin ) so that the body lies in the plane, and the axis is perpendicular to the plane of the body. Let Ix, Iy and Iz be moments of inertia about axis x, y, z respectively, the perpendicular axis theorem states that This rule can be applied with the parallel axis theorem and the stretch rule to find moments of inertia for a variety of shapes. read less

The perpendicular axis theorem (or plane figure theorem) can be used to determine the moment of inertia of a rigid object that lies entirely within a plane, about an axis perpendicular to the plane, given the moments of inertia of the object about two perpendicular axes lying within the plane. The axes must all pass through a single point in the plane. the parallel axis theorem, also known as Huygens–Steiner theorem after Christiaan Huygens and Jakob Steiner, can be used to determine the mass moment of inertia or the second moment of area of a rigid body about any axis, given the body's moment of inertia about a parallel axis through the object's center of mass and the perpendicular distance between the axes. read less

Parallel axis theorem: It states that if there are two axes of rotation one being at the center of mass, then the moment of inertia can be written as~ Iab = Ixy = Md^2 Perpendicular axis theorem: If two axes x and y are perpendicular to each other, then the moment of inertia about z axis which is perpendicular to the xy plane is given as~ Iz = Ix = Iy read less