How is this "perpetual motion" mechanism violating physics?

Question

I have here a lever with an equal weight on each end, but the weight on the right is offset and spins on a frictionless bearing.

When the weight is extended, the moment on that side is higher and drives the lever downwards, but when the weight is on the inside the moment is less and drives the lever upwards.

But that forms a perpetual motion machine, so I must be doing something wrong. But I can't for the life of me figure out what.

To be clear: as envisioned, torque is being applied. Work is being done. The gravitational potential energy of the system never changes, but its kinetic energy does. A marble placed on the lever at the bottom could ride the lever to the top, and then roll down a slide and get on at the bottom again.

Yes, I know that frictionless bearings are hypothetical. But even with frictionless bearings a machine shouldn't be able to do work - it should just spin aimlessly.

Answer 1

This seems like the same mechanism as "pumping" a playground swing, where you change the shape of the mass at the end of a pendulum in resonance with the oscillation and the size of the oscillation increases. In that case, the energy required to raise the swing comes from the muscles of the person who is riding the swing and changing their posture.

As commenters have pointed out, in a frictionless world you can have eternal motion, such as a frictionless pendulum. It's not clear how you might extract energy from this lever.

Answer 2

It cannot work. If you start from horizontal and extend the left arm, it will turn around to become vertical, and the potential energy will change from $E_p=0$ to $E_p=mgd-mg(d+l)=-mgl$, where $l$ is the extra length that extended the initial arm of length $d$, which now is pointing down. You got kinetic energy that you saved in some other form, so it is now vertically at rest. In order to move the extension inwards to get it back to horizontal, you have to move the extended wight upwards, thus you need to give back the energy you initially saved when it moved downwards.