Perpendicular Axis Theorem
A theorem stating that for a thin planar lamina, the moment of inertia about an axis perpendicular to the plane equals the sum of moments of inertia about two perpendicular axes in the plane.
Governing formula
Iz = Ix + Iy
SI unit
kg·m²
In depth
Applicable strictly to flat 2D thin plates, this theorem simplifies polar moment of inertia calculations.
Examples in the real world
Finding the perpendicular polar moment of inertia of a flat circular disc from its planar diameter moments.