Sphere versus Cylinder
The blue object in the figures is the
side view of a cylinder with the
same radius and volume (mass)
as the orange object (a sphere).
Note that most of the mass is
in the same place, but the top
and bottom of the sphere must
be moved away to provide the
corners for the cylinder. Hence, the Moment of
Inertia of the cylinder is slighly larger than that of
the sphere: Isphere = (2/5)MR2 ; Icylinder = (1/2)MR2 .