> … rotation of [a rigid body with three distinct principal moments of inertia] around its first and third principal axes is stable, while rotation around its second principal axis (or intermediate axis) is not.

This video has a more examples and a detailed explanation:

>The video of a tumbling T-handle on the International Space Station is a wonderful illustration of the instability of rotation about an asymmetric object’s intermediate principal axis. This instability is also known as the Dzhanibekov effect after the Soviet cosmonaut Vladimir Dzhanibekov who discovered this effect on the MIR space station in 1985. The T-handle’s rotational motion is well approximated by considering the object to be rigid and modeling its rotational behavior via a balance of angular momentum.

Not using the fancy words, but it’s because it’s symmetric in size and weight across 2 out of 3 axis. So when it spins, it’s out of balance across one axis, the axis where its up & down where the handle is on one side and other side doesn’t have the handle. The perfect balance on 2 axis means that its balanced and doesn’t produce any change when spun. Others have posted more technical videos and description links

You can do the same thing with your phone. If you throw it up in the air to spin about the intermediate axis, meaning the rotation axis is aligned with the medium or middle moment of inertia, it is impossible to toss your phone about this axis without doing a flip on every other rotation.

There are three ways it can spin. It spins around itself in two of those ways. In the third way, it flips around a spot outside of itself; that spin is unstable. So if it wobbles while spinning, the wobble will push it into the closest stable spin in that direction.

Take a twizzler and stick it in a battery drill. Point it downward and spin it slow, them faster, then faster… As the speed increases, the twizzler spirals outward.

That’s kinda what happens to the odd bit poking out the side… It has the tiniest little imbalance, and that makes it twizzler outwards a teensy tiny little bit, then once it’s twizzlered out a little, it’s more imbalanced, so it twizzlers some more, and more imbalance, and keeps growing… It all happens in a tiny little amount, but it grows exponentially until the twizzlering overcomes the flywheel effect of the balanced part, then it all goes wonky as shit until the twizzlery bit loses all it’s mojo and the flywheely bits kick back in and floop the whole works over and it starts twizzlering the other side.

This is a demonstration of the [tennis racket theorem](https://en.wikipedia.org/wiki/Tennis_racket_theorem) in microgravity, where it’s easier to observe:

> … rotation of [a rigid body with three distinct principal moments of inertia] around its first and third principal axes is stable, while rotation around its second principal axis (or intermediate axis) is not.

This video has a more examples and a detailed explanation:

[The Bizarre Behavior of Rotating Bodies, Explained](https://www.youtube.com/watch?v=1VPfZ_XzisU)

Step 1 go to space

Step 2 spin a T shaped thing

>The video of a tumbling T-handle on the International Space Station is a wonderful illustration of the instability of rotation about an asymmetric object’s intermediate principal axis. This instability is also known as the Dzhanibekov effect after the Soviet cosmonaut Vladimir Dzhanibekov who discovered this effect on the MIR space station in 1985. The T-handle’s rotational motion is well approximated by considering the object to be rigid and modeling its rotational behavior via a balance of angular momentum.

[Rest of the article about this video including math and computer simulations here.](https://rotations.berkeley.edu/a-tumbling-t-handle-in-space/)

The intermediate axis theorem

Check veritasium’s video on youtube

He explains the shit really well

Not using the fancy words, but it’s because it’s symmetric in size and weight across 2 out of 3 axis. So when it spins, it’s out of balance across one axis, the axis where its up & down where the handle is on one side and other side doesn’t have the handle. The perfect balance on 2 axis means that its balanced and doesn’t produce any change when spun. Others have posted more technical videos and description links

Dzhanibekov effect.

I think there’s a video on the Veritasium YouTube channel about it

Something something harmonic node switching, something something, broken symmetry.

You can do the same thing with your phone. If you throw it up in the air to spin about the intermediate axis, meaning the rotation axis is aligned with the medium or middle moment of inertia, it is impossible to toss your phone about this axis without doing a flip on every other rotation.

Yes, someone could

Others like [Codebender](https://www.reddit.com/r/physicsgifs/comments/nrihx3/could_someone_explain_how_this_do/h0gnqdh/) have done a great job explaining what’s happening! Let me take a stab at a heavy simplification that I can understand without post-secondary physics.

# In r/eli5 style

There are three ways it can spin. It spins around itself in two of those ways. In the third way, it flips around a spot outside of itself; that spin is unstable. So if it wobbles while spinning, the wobble will push it into the closest stable spin in that direction.

Here https://mathoverflow.net/questions/81960/the-dzhanibekov-effect-an-exercise-in-mechanics-or-fiction-explain-mathemat

Take a twizzler and stick it in a battery drill. Point it downward and spin it slow, them faster, then faster… As the speed increases, the twizzler spirals outward.

That’s kinda what happens to the odd bit poking out the side… It has the tiniest little imbalance, and that makes it twizzler outwards a teensy tiny little bit, then once it’s twizzlered out a little, it’s more imbalanced, so it twizzlers some more, and more imbalance, and keeps growing… It all happens in a tiny little amount, but it grows exponentially until the twizzlering overcomes the flywheel effect of the balanced part, then it all goes wonky as shit until the twizzlery bit loses all it’s mojo and the flywheely bits kick back in and floop the whole works over and it starts twizzlering the other side.

Pretty sure that’s how it do 🙂

Well.. go to 0 gravity for staters…

Scott Manley has some great, comprehendible videos on this topic

Ze Frank reference for the win!!

That’s a cute hummingbird!