←back to thread

A new pyramid-like shape always lands the same side up

(www.quantamagazine.org)
584 points robinhouston | 2 comments | 25 Jun 25 20:01 UTC | HN request time: 0s | source
Show context
ChuckMcM ◴[25 Jun 25 21:09 UTC] No.44381861[source]▶
Worst D-4 ever! But more seriously, I wonder how closely you could get to an non-uniform mass polyhedra which had 'knife edge' type balance. Which is to say;

1) Construct a polyhedra with uneven weight distribution which is stable on exactly two faces.

2) Make one of those faces much more stable than the other, so if it is on the limited stability face and disturbed, it will switch to the high stability face.

A structure like that would be useful as a tamper detector.

replies(12): >>44382132 #>>44382239 #>>44382240 #>>44382291 #>>44382682 #>>44382693 #>>44382719 #>>44382821 #>>44384580 #>>44384845 #>>44385378 #>>44387476 #
1. Evidlo ◴[25 Jun 25 21:51 UTC] No.44382132[source]▶
> A structure like that would be useful as a tamper detector.

Why does it need to be a polyhedron?

replies(1): >>44382207 #
2. ChuckMcM ◴[25 Jun 25 22:03 UTC] No.44382207[source]▶
I was thinking exactly two stable states. Presumably you could have a sphere with the light end and heavy end having flats on them which might work as well. The tamper requirement I've worked with in the past needs strong guarantees about exactly two states[1] "not tampered" and "tampered". In any situation you'd need to ensure that the transition from one state to the other was always possible.

That was where my mind went when thinking about the article.

[1] The spec in question specifically did not allow for the situation of being in one state, and not being in that one state as the two states. Which had to do about traceability.