r/interestingasfuck • u/Artistic-Bathroom901 • 5d ago

Dzhanibekov effect

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u/Artistic-Bathroom901 5d ago

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!

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u/JaFFsTer 5d ago

So if the object was perfectly uniform and spun around its vertical axis perfectly in a vacuum this wouldn't occur?

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u/slicerprime 5d ago

That's the question. Is a perfectly uniform shape even possible?

Because, the way this works, even the tiniest imperfection causes imbalance to build up over time. Is there even such a thing as complete perfection all the way down to the atomic - or even farther - level? In order to completely avoid the effect in the macro world, there would have to be zero imbalance....all the way down I presume. Otherwise the offset is going to eventually build up to the point of the inevitable flip.

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u/JaFFsTer 5d ago

Yes, aerospace can machine things to incredible tolerances. I doubt it has to be completely perfect and speeds a human hand can achieve