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Recently I was using multibody dynamics software at work and when I ran the simulation it warned me that the values that I specified for the inertia tensor of one of the bodies was physically impossible. It turned out that I had mistyped one of the values and it was an easy fix, but it got me thinking - how did it know?

After some searching I found a source (which I cannot remember now) that said the sum of any two principle moments of inertia for an object must be greater than the third. After some testing of different shapes I think that this is true, but why? Is there a derivation anywhere? None of my textbooks mention this at all and the one source that I did manage to find didn't provide an explanation.

Thanks for your help!

-Kerry

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# Valid Inertia Tensor

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