Moment of Inertia of a Composite Area

[only_huce]

This is not so much a problem as it is a conceptual question. You're calculating the moment of inertia of a composite shape, let's say a square and a triangle. The square however has a hole inside of it. How does this change the computation of the moment of inertia? This is in a 2-D plane.

My guess would be that it only affects the area of the square but not any part of the calculation involving x or y.

 

[tiny-tim]

You're calculating the moment of inertia of a composite shape, let's say a square and a triangle. The square however has a hole inside of it. How does this change the computation of the moment of inertia? This is in a 2-D plane.

Hi only_huce!

Moment of inertia is additive, so you just add for solid shapes, and you subtract for holes.

In other words: do it for the complete square, then do it for the same material with the shape of the hole, and subtract.