The tennis racket theorem or intermediate axis theorem is a result in classical mechanics describing the movement of a rigid body with three distinct principal moments of inertia. It is also dubbed the Dzhanibekov effect, after Russian cosmonaut Vladimir Dzhanibekov who noticed one of the theorem's consequences while in space in 1985 although the effect was already known for at least 150 years before that and is well described in contemporary texts on classical mechanics that would have been known to Dzhanibekov. An article explaining the effect was published in 1991.The theorem describes the...