Again, we will need to describe this with an mathematical function if the height is not constant. Moving from left to right, the rate of change of the area will be the height of the shape at any given \(x\)-value times the rate at which we are moving left to right. This free multi-purpose calculator is taken from our full suite Structural Analysis Software. The polar section modulus (also called section modulus of torsion), Z p, for circular sections may be found by dividing the polar moment of inertia, J, by the distance c from the center of gravity to the most remote fiber. \)) we will move left to right, using the distances from the \(y\)-axis in our moment integral (in this case the \(x\) coordinates of each point). Another useful exercise is to look at this all by considering the general moment of inertia circle formula: Ix,Iy 64D4 I x, I y 64 D 4.