  : You can use polar moment of inertia to calculate the rotational inertia of an object with constant cross-section: :: : where I is the rotational inertia of the object, :  is the polar moment of inertia of the cross-section of the object, :  is the density of the material,  : and l is the length of the object. : Unlike the torsion application, this is true for every cross-sectional shape, even non-circular shapes. :   