The general formula for moment of inertia is:

Question

I = Sigma mi * ri^2

(mi is mass of atom, ri is distance to axis of rotation)

In a diatomic molecule, the moment of inertia is

I = ma*mb(ma+mb) * R^2

(R is distance between atoms, ma and mb are masses of two atoms)

How is the diatomic molecule formula derived from the general formula? The two do not appear connected.

Answer 1

You can find a proof in the web page below:

http://www.tutorvista.com/content/physics/physics-iii/rigid-body/diatomic-molecule.php

The symbols used are different but equivalent to the ones you are using. The general formula is not given explicitly but it is applied anyway.

Answer 2

GK, thank you so much. That was exactly what I was looking for!