# Mass moment inertia of object displaced from axiz

## Main Question or Discussion Point

Hey y'all,

A plea for general advice here as I embark on a project. Say I have an object rotating around an axis but *displaced* some distance "r" from that axis. It's length, a dimension perpendicular to the axis, is "a." I'm interested in finding the mass moment of inertia for the object. As I see it, I have two choices: (1) develop an integral describing the mass distribution of the object around the axis and then use the fundamental theorem and the interval r to r+a or; (2) use the parallel axis theorem, that is, develop definitive integrals describing both the mass distribution of the object at r=0 and around the axis at r->r+a, summing the two. So real simply, fundamental theorem or parallel axis theorem?

Thanks!

PTC

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BruceW
Homework Helper
I never really got my head round the parallel axis theorem, so I would use 1), which should be fairly easy, since the object is pointing straight away from the axis, it makes the integral fairly simple.

Thanks, Bruce! That's just about what I figured--it'd be much easier to compute over the interval. Thanks again!

PTC