Moment of inertia is supposed to be defined with respect to a rotational axis such that for a system of point masses, I=∑m(adsbygoogle = window.adsbygoogle || []).push({}); _{i}r_{i}^{2}where r_{i}'s are the perpendicular distances of the particles from the axis.

However, in some derivations of the virial theorem (like the one on wiki), the so-called "scalar" moment of inertia, the r_{i}'s are taken to be the magnitude of the position vectors of those particles with respect to the origin without reference to any axis. My question is, does it still have the same physical significance as its ordinary counterpart? This quantity at most indicates the overall separation of the particles from the origin

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# I "Moment of Inertia" in Virial Theorem

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