I was watching a light pull swinging (after it had been used),
the (heavier) weight of the pull, on the end of the cord,
made the lower part of the cord
swing much more (than towards the top...)

I thought:
H'mm. If a bit of energy makes the cord move at the top,
would a greater amount of energy be produced at the bottom
(of what is a pendulum)?
(If that could be replicated, captured...)

Sorry if not described very clearly!
I hope you're following me?