I'm looking for an intuitive argument for the intermediate-axis
theorem (IAT), rather than a formal derivation via Euler's equations.
Recall that the IAT says that if you throw a book (taped closed) or
tennis racquet into the air with spin, it will start tumbling about
its intermediate principal axis, in contrast to the stable rotation
observed about its large and small axes.
I don't expect an actual proof, but just a plausibility argument at
the introductory level.Something to the effect of "It makes sense
that rotation is not very stable about the intermediate axis because
..." or "It makes sense that rotation is quite stable about the large
and small moments of inertia because ...."