What is the word for something if it is self-reliant for energy needs to work?
Interesting question, but strictly speaking there is nothing that can be totally self reliant in energy needs cause that would essentially mean the creation of energy from nothing. Even the sun relies on "burning" hydrogen to produce the vast amount of energy it does, when the hydrogen in the sun will be depleted it ll stop producing energy.
Context matters, but it sounds a bit like you are referring to perpetual motion.
an electron in a stationary state in an atomic orbital requires zero energy and depending on what model you choose you could say it is moving in an "orbit", I use the term loosely.
not sure but I think it requires no energy for a charged particle to maintain a circular orbit in the classical sense in a magnetic field altho the magnetic field takes energy to create and sustain.
disclaimer: non-pro attempting an answer.
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