B Upside down buoyancy (Have you seen this?)

[kuruman]

Devilishly clever.

 

[Dale]

Cool. I had definitely never heard of that before.

 

[Motore]

Here is the accompanying article:
https://arxiv.org/abs/2003.04777

 

[A.T.]

Here is the accompanying article:
https://arxiv.org/abs/2003.04777

So the floating equilibrium on the bottom surface is actually unstable based on static potential energy alone (Fig 3B). The stability comes from dynamic effects of the oscillation, which take like 5 pages of supplementary text to explain.