Talk:polar moment of inertia

Polar moment of inertia Izc = Ixc + Iyc describes the ability of the shape to resist rotation by its inertia, not by its torsional stress. It is a section property and it is equivalent to the body moment of inertia Izc for a thin disk with the respective section and unit thickness and mass. If we have a prismatic body with the respective section and length L, and apply angular acceleration 'a' about zz axis, rotational inertia moment will be produced: T = a*Izc*L*[mass density].

It should not be confused with Torsional Constant which is also a section property. It describes the ability of prismatic beam with the respective section to resist St. Venant torsion by internal shear stresses.