Bernt - If you prefer to see certain forces as existing without performing work, then you are free to perceive the world functioning in that manner. I think that if a force exists and it is operant, then it is performing work - even if the object remains stationary. So, in your example of a person standing stationary, you do not see any "work" because the object is stationary. I see "work" - because muscles forces are required to keep the person stationary and erect in the presence of gravity. If body muscles weren't actively working to oppose the force of gravity, then the person would fall to the ground.
Consider this ice rink example.
In this example, person B is applying a push-force at a 180 degree angle to person A's push-force. If the push-forces are equal, then the object will remain stationary and not move in a straight line direction towards destination D or along a circular path towards position C.
If the object remains stationary, you may "feel" that person A and person B are not working. However, in my mental universe, both person A and person B are working just as hard as before (as in those previous examples) because they are supplying the same amount of push-force (energy) as before - the only difference is that their push-forces are working in perfect opposition thereby eliminating any possibility of there being any net force available to move the object on the ice rink.
According to Newtonian physics - forces can be in a state of balance that results in an object being stationary.
Note that it states the following with respect to Newton's first law of motion = An object at rest tends to stay at rest and an object in motion tends to stay in motion with the same speed and in the same direction unless acted upon by an unbalanced force.
In other words, it takes an unbalanced force to disturb a an object from its position of rest. If the forces are in balance, then the object will remain at rest - even though the forces are working.
You wrote-: "Regarding your curve pattern. You could put up a fence that forces the object to turn. The forces from this fence will not use any energy and they will not work. Still they will do the same "work" as the centripetal components in your examples."
The fence is working in a Newtonian sense - by providing an unbalanced force that deflects the object.
It states with respect to a person riding in a car.
"Have you ever experienced inertia (resisting changes in your state of motion) in an automobile while it is braking to a stop? The force of the road on the locked wheels provides the unbalanced force to change the car's state of motion, yet there is no unbalanced force to change your own state of motion. Thus, you continue in motion, sliding along the seat in forward motion. A person in motion tends to stay in motion with the same speed and in the same direction ... unless acted upon by the unbalanced force of a seat belt. Yes! Seat belts are used to provide safety for passengers whose motion is governed by Newton's laws. The seat belt provides the unbalanced force which brings you from a state of motion to a state of rest."
In this example the book on the table is at rest - because the table top is providing a force to balance the force of gravity.
Therefore, inanimate objects can provide an unbalanced force that changes a state of motion to a state of rest. An unbalanced force can also cause a change of direction - as in the examples I have previously supplied (where person B supplied the unbalanced force that deflected the object) or in the presence of a fence which provides the unbalanced force that deflects the object.
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