This problem actually came up during a discussion about "is there a perfect circle in the nature, or can it be constructed?" I came up with this answer, thinking that an elastic charged ring would assume the shape of a circle in equilibrium. But now that I realize the complexity of the problem...
Thanks for the replies. Actually no, I asked just out of curiosity.
Perhaps the best way is actually putting a charged necklace on a table and observing the behavior :)
But I would guess someone had at least written the equations in some book or article. It is an easy problem to think of...
Suppose we have a necklace made of a conducting material. We join the two ends and leave it on a frictionless non-conducting table. Then we charge it negatively. What is the equilibrium shape of the necklace? The answer to this is probably a circle. I am actually looking for the differential...