This idea was proposed by a great philosopher and thinker of our time, who we will simply refer to as “Reno S” here.

Imagine a spool, hanging from a spring above a magnet. If you run a current through the spool, it will generate a magnetic field, causing the spool to be pulled towards the magnet. If the current flow is stopped, the spool will recede away from the magnet thanks to the spring. This backwards motion may be used to generate electricity: as the spool moves back through the magnetic field of the magnet below, it will generate a current.

At first you'd think this can't work given that you won't get enough current out of the system to pull the spool as much as the initial current managed to do. But here is the thing: the force pulling down the spool will depend on the strength of the magnet below. You could use a HUGE magnet, pulling the spool down a lot. In that case, this system should produce more energy than is needed to keep it running. Or would it?