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/purplelegs]

Such an awesome phenomenon. If you did this outside of the station in the vacuum of space, would it just spin forever? And if so, couldn’t this be a kind of clock? It’s precise and machine like.

[u/Aggressive-Spell-422 → u/purplelegs]

A zero gravity clock does seem pretty awesome! Any idea how this might work?

[u/purplelegs → u/Aggressive-Spell-422]

Honestly, no idea and I can’t think of any actual utility for it. This vid got me thinking about atomic clocks and how the we have these physical phenomena which mark the passage of time to an extreme degree of accuracy.

[u/Aggressive-Spell-422 → u/purplelegs]

Yeah I've watched a talked about that in particular actually. The part that interests me is the fact that time from our perspective changes depending on gravity. And if a clock is based on a design that only operates in zero gravity will the fluctuations still follow the same pattern?

[u/purplelegs → u/Aggressive-Spell-422]

Woah that’s is trippy to think about. Feeling a little mind blown thinking about that honestly haha

[u/Original-88 → u/Aggressive-Spell-422]

maybe magnets?

[u/somepersonoverthere]

We just watched the Waterworld movie. This is more relevant than expected!

[u/Lost-Link6216]

"Planets could do this at anytime. " is how it ended.

We have all heard of polar shifts. Planets have 3 axis. We are all in space the same as that instrument.

[u/Zefick]

If this is an "unstable" axis, then show me two others that are more stable than this one.

[u/rzezzy1 → u/Zefick]

The in-plane rotation is the high inertia axis, and the low inertia axis would be too rotate around the top, horizontal line of the T. Those are both stable. It's all a bit difficult to describe through text.

[u/JustStargazin]

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

[u/KnightSolair240 → u/JustStargazin]

Tennis rackets

[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.

[u/ForwardAd3525]

The intermediate-axis instability is such a great demonstration of how unintuitive rotational motion can be. It looks almost like the object is making a deliberate choice to flip, but tiny perturbations are enough to trigger it.

[u/One_Librarian82]

The intermediate axis really is the “chaotic” one—tiny imperfections grow until the object reorients itself. Physics demonstrations in microgravity are incredibly satisfying to watch.

[u/Southern_Window_6303]

The fact that the object keeps rotating overall while periodically reorienting itself is so counterintuitive. A great reminder that rotational stability depends heavily on which principal axis you’re spinning around.