Dzhanibekov effect demonstration in microgravity, NASA.(Tennis racket theorem)
Why Physics Stack Exchange recommends it
Physics Stack Exchange users link it as a concrete visual example of rotation about an unstable intermediate axis when explaining rigid-body dynamics and angular momentum conservation.
Recommended by 1 people across 1 different months, 2020 to 2022.
What it is
A 31-second clip of a NASA microgravity demonstration showing a free-floating object that flips suddenly while spinning, known as the Dzhanibekov effect or tennis racket theorem. The description briefly explains the intermediate axis theorem for rigid bodies with three distinct principal moments of inertia.
What people said
Recommends John Alexiou · 2020-01 · Physics Stack Exchange · on “Do objects rotate around the torque vector or its center?”
@ViniciusACP - In real life it is very difficult to apply a pure torque. In the example you mentioned the net force must be such that the center of mass accelerates. In fact playing with a pencil in your hands, you are fixing the rotation axis to be between your fingers and letting the contact force be whatever it need to be as such. It is really hard to impose a torque without applying a force. The best example I can think of is the magnetic stirrers they use in chemistry labs. Also look at this [this video] . The center of mass moves in a straight line.
Cites KF Gauss · 2020-09 · Physics Stack Exchange · on “Is there a quantum analogue of the "Tennis Racket" theorem?”
A non-trivial result from studying the classical mechanics of an extended object shows that rotation about an axis whose moment of inertia is between the largest and smallest moment-of-inertia axes is unstable. This is known as the "tennis racket" theorem, as described on the Wikipedia page. In essence, there are two axes which are easy/stable to rotate around, and one which is unstable. The basic idea of the tennis racket theorem has little to do with gravity or air resistance, rather it is a statement about the sensitivity of the rotation axis to the axis of the initial torque kick. Very nice videos demonstrating this concept can be found on YouTube. For example this one [this video] . My quest
Cites Claudio Saspinski · 2022-05 · Physics Stack Exchange · on “Can conservation of angular momentum be proven?”
Angular momentum for rigid bodies is conserved even for complicated movements, when the axis of rotation chnges all the time.https: [this video]
Cites John Alexiou · 2022-10 · Physics Stack Exchange · on “Can there be any change in angular velocity without internal torque if angular momentum is to be conserved?”
Yes, you can have changes to rotational velocity with no external torque if the object is not rotating about any of the three principal axes of rotation. One example is the Dzhanibekov effect [this video] where a free object (in space) changes orientation completely and suddenly all on its own. Also, for a system of rigid bodies, you can indeed sum up with the total rotational momentum just as you sum up the total translational momentum $$ \begin{aligned} \boldsymbol{p}_{\rm total} & = \sum_i \left( m_i \boldsymbol{v}_i \right) \\ \boldsymbol{L}_{\rm total} & = \sum_i \left( \mathcal{I}_i \boldsymbol{\omega}_i + \boldsymbol{r}_i \times (m_i \boldsymbol{v}_i) \right) \end{aligned} $$ where $m_i$ i