Is energy, as we know it, "persistent"?

Question

Suppose I raise a ball (with my hand) to some height. I am doing some work against gravity and storing potential energy in the ball.

However, once I loosen my grip, or just sweep my hand away from under the ball, the ball falls down.

As long as the force existed, the work done and hence the potential energy gained existed. Force gone, work gone. I know, I know. When the ball fell down it released the PE into KE. But read on.

I try pushing a wall. It doesn't move. Physicists come to the spot and shout, HAHA LOSER. No work done.

Why did I sweat then? What did I invest my energy into? I mean it gotta go somewhere. I can predict that I may have wasted my energy into heat. But just that?

On the other hand, the wall stood still without investing any energy at all. Because of chemical forces. Chemical bonds that held it firm.

So only "human" or non-natural forces do work that only exists till they themselves exist? As soon as they withdraw, the work done transforms?

Is work supposedly be this kind of a retentive investment? One that an agent is supposed to keep maintaining? Aren't we just supposed to do a work and come back and relax knowing that it'll stay the way it is? Why do states of work done change for non-natural processes whereas it resides in equilibrium for natural ones?

Naturally, would it be too unrealistic for one to state that energy is not an investment that persists, but a labour that has to be retained continually?

I know also that a possible answer to all my questions would be entropy. Just find which process or pathway maximises universal entropy. Nature chooses that.

But then, on a more metaphysical note, why are we, life, even exisiting? It's against naturality...

Answer 1

Why did I sweat then? What did I invest my energy into?

Your body is a complicated biological machine. When your muscles contract, small muscle fibers are continuously sliding against one another (see e.g. this biology text). Pushing against a stationary wall is an isometric exercise, in which no visible motion of the joint occurs. Nonetheless, these small muscular filment contractions still occur (generating heat, small amounts of sound, etc but doing no mechanical work on the wall) and it is there that your body's stored chemical energy goes.

On the other hand, if the object you exert a force on can move then the force you apply will do some mechanical work on it. As a result, some of the energy you burn will go into work and the remainder will be lost as heat, just as before. The human body is not a particularly efficient engine (apparently around 25% or so), so most of your energy goes to the latter.

So only "human" or non-natural forces do work that only exists till they themselves exist? As soon as they withdraw, the work done transforms?

I don't really know what you mean here. Work is not a thing which exists for some amount of time - it is a quantity which is associated to a process. When an object moves along a path through space under the influence of a force, then that force does some amount of work. How much work is done depends on the force and the path.

In particular, work is not a "state variable". It is not a meaningful question to ask "how much work has ever been done on this ball." It only makes sense to ask how much work is done along a particular path by a particular force.

But then, on a more metaphysical note, why are we, life, even exisiting? It's against naturality...

This is not a physics question, so I can't address it (or the remainder of your post) here.