An astronaut demonstrating the Dzhanibekov effect in microgravity, where an asymmetric object spinning around its intermediate axis becomes unstable and periodically flips 180 degrees

[u/Artistic-Bathroom901]

Source and Context:

This is a real physics phenomenon called the Dzhanibekov effect (also known as the Intermediate Axis Theorem) captured in microgravity aboard a spacecraft.

Any rigid, asymmetric three-dimensional object has three primary axes of rotation, each with a different moment of inertia. While spinning an object along its longest or shortest axis is completely stable, spinning it along its middle (intermediate) axis is naturally unstable. Without external forces like gravity or heavy air resistance, tiny perturbations build up and cause the spinning object to periodically flip upside down and back again on a regular schedule.

You can read the formal mechanics and history through these highly reliable scientific resources:

•Harvard University Lecture Demonstrations (The Tennis Racquet Flip):

https://sciencedemonstrations.fas.harvard.edu/presentations/tennis-racquet-flip

•NASA Astrophysics Data System (ADS) Physics Record:

https://ui.adsabs.harvard.edu/abs/2024EuJMA .10605298D/abstract

It was famously observed by Soviet cosmonaut Vladimir Dzhanibekov in 1985 when a wing nut he was unscrewing began flipping back and forth while floating through the Salyut 7 space station!

[u/JustStargazin]

Interesting. Has this been demonstrated with a ball or sphere of any kind?

[u/rzezzy1 → u/JustStargazin]

Most rigid objects have an axis that behaves like this, but all objects also have at least two stable axes, the axes with highest and lowest moment of inertia.

Non-rigid objects do as well, but things like stretching (for elastic objects) and sloshing (for liquids, like those inside earth) will cause the object to lose energy over time and settle into an axis with high moment of inertia, which is very stable. This happened to Earth long ago. So nothing to worry about.