I had a friend share an idea with me, and i said it was wrong, but he wouldn't believe me, mostly because i'm a layman and couldn't give more evidence than 'if it was that easy someone would've thought of it', or 'it's too close to perpetual motion which is impossible'. The idea is you have a wheel system, (two wheels, one big one small, connected by a chain running around the outside, similar to a bicycle gear system) For simplicity say 1 turn of the big wheel causes 2 turns of the smaller wheel. That's fine, correct? Now he says suppose the smaller wheel has a rod connecting it's center to the center of another big wheel positioned right beside it. That big wheel is in turn connected by chain to another small wheel, which is positioned back next to the original wheel, also having a rod connecting its center to the original big wheel, creating a loop. My friend says since 1 turn of the first wheel causes 2 turns of the second, which should turn the big wheel its connected to by a rod through their centers 2 turns as well. Now 2 turns of this big wheel would turn the second small wheel 4 turns. That's all fine, right? But he says that last wheel will turn the original wheel 4 times as well, causing the next wheel to turn 8 times, and so forth etc. He says it just keeps turning on itself, in some sort of positive feedback system. I tell him that's too close to perpetual motion, but he wants an actual answer why it wouldn't work, which i couldn't really give on my own.