Originally a test comparing the 'shakiness' of spheres to boxes--spheres are stable while boxes shake if stacked.
However, I got sidetracked into making a loop. Strangely, attempting to update the position of an entity with a dynamic-body failed (nothing happened). The work-around is to remove the dynamic-body, re-position, and then add the dynamic-body component once-more (i.e. turn physics off for the entity, move, and then turn it on again).
Updated missing url https://cdn.rawgit.com/donmccurdy/aframe-extras/8a76a783c2ba3d4779e92a892cc31fb0757fa4df/dist/aframe-extras.physics.min.js to https://cdn.jsdelivr.net/gh/donmccurdy/aframe-extras/8a76a783c2ba3d4779e92a892cc31fb0757fa4df/dist/aframe-extras.physics.min.js
https://aframe.io/releases/0.3.0/aframe.min.js
https://d3js.org/d3.v4.min.js
https://cdn.rawgit.com/donmccurdy/aframe-extras/8a76a783c2ba3d4779e92a892cc31fb0757fa4df/dist/aframe-extras.physics.min.js