A sample of this motor:
[https://www.youtube.com/watch?v=LXBYMiNH1nE](https://www.youtube.com/watch?v=LXBYMiNH1nE)
In: 87
The simplest answer is that there’s no way to *create* energy^0, only move it from one place / form to another, so a machine can only continue to move if you either *add* energy (like a motor with a power supply – not a “perpetual motion machine”) or have *zero* friction, which just isn’t possible^1.
If you don’t add energy to a “perpetual motion machine” then any energy *lost* will not be replaced, and the whole thing will eventually stop. There’s always going to be some form of friction that converts some of the kinetic energy (energy of movement) into heat, which is basically lost^2
Therefore, unless you either (a) break the rules of the game by adding energy into the machine, (b) break the laws of physics by *creating* energy, or (c) break the laws of physics by having no losses, the engine will stop and isn’t in “perpetual motion” even if it takes quite a long time to stop.
These principles are true no matter what form the mechanism takes, magnetic / electric / kinetic / whatever, the same fundamental limits always apply.
TL;DR: [Ginsberg’s Theorem](https://en.wikipedia.org/wiki/Ginsberg%27s_theorem) puts it succinctly:
0. There is a game. ([0th law of thermodynamics](https://en.wikipedia.org/wiki/Zeroth_law_of_thermodynamics))
1. You can’t win. ([1st law of thermodynamics](https://en.wikipedia.org/wiki/First_law_of_thermodynamics))
2. You can’t break even. ([2nd law of thermodynamics](https://en.wikipedia.org/wiki/Second_law_of_thermodynamics))
3. You can’t even get out of the game. ([3rd law of thermodynamics](https://en.wikipedia.org/wiki/Third_law_of_thermodynamics))
^0 I’m going to slightly side-step the fact that energy and matter are interchangeable, as fusion / fission are never part of these discussions. Just counting “mass” as a form of energy means the logic ends up essentially the same, though.
^1 In practical terms, it’s just not possible to remove all sources of friction, but even *in principle* there’s no way to avoid *some* form of loss – the laws of thermodynamics are the most certain of all our physical laws.
^2 You can only make heat energy do work when there’s a *difference* in temperature, and even then [not all of it can be used](https://en.wikipedia.org/wiki/Carnot%27s_theorem_(thermodynamics)). To use the heat energy, you have to have something else with a lower temperature, which you will heat up in the process. The final state is that all the energy is in the form of heat^3, but with the entire universe at the same temperature, there’s nothing “cooler” to give a temperature difference that can be used to make the energy do work for you.
^3 Re-introducing the mass / energy equivalence, in the trillions-of-years-into-the-future version of the end state, even all the mass ends up decaying into photons, but it does admittedly take a [fair while](https://en.wikipedia.org/wiki/Future_of_an_expanding_universe) and involve some physics we’ve not really had time to *witness* happening as such. The *general shape* of the end result is pretty certain, though.
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