Several similar questions have been asked, e.g. this one, but all of them used the example of muscle work, so it was clear where the energy went. However, suppose we suspend an object on a rope from the ceiling. We come 20 years later and find the object hanging where we left it. I understand that no mechanical work is being performed here. However, it seems counter-intuitive that this holding of the object is achieved for free. So, what has been happening energy-wise during these 20 years and what observable changes did that result in?
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Nothing.
You seem to wonder why no energy is spent. But why would it?
In general, a force does not spend energy. Some forces do (the human body, a rocket, kinetic friction, gravity during free fall) and some forces don't (normal force, tension forces, gravity when stationary). It is not a general rule that energy is spent for a force to exist.
Those that do spend energy, do so because of the "machine" that creates them (the human body spending nutritions, the rocket spending fuel) or because they do work on an object by their very nature (kinetic friction expelling heat, gravity converting stored potential energy to/from kinetic energy).
But the rope in your example doesn't spend any energy. All that may happen is deterioration of the material due to corrosive chemical processes. In a vacuum that wouldn't happen. In ideal conditions, the rope can keep up its tension force forever.
Steeven
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