- #1

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I know what a moment of inertia is. I know what they represent, I know how to use them, I even know how to calculate them from scratch if need be.

But I don't know

**why**they are what they are.

Why is it that this weird value with seemingly random d^2 terms provides the mass distribution about an axis?

Probably more to the point:

What, conceptually, is a tensor?