Our advice
Represent a technical system according to the law of integrality of parts

In any study, there are many possible Tool-FPU-Object associations. It's imperative that you have a coherent starting triptych by asking yourself the following question: "If I eliminate the object from the face of the earth, does my tool still make sense?" If the answer to such a question is "no", then you probably have the right tool-object combination.

The UPF must cause the object to change state. For example, you can try to identify which physical quantity changes from one state to another when the tool performs the UPF. In the example of the hammer, this would mean identifying that the value at which the nail is driven changes from L0 (0 mm) to L1 (total length of the nail).

Preferably identify the motor element first (the one that receives energy and transforms it), then the work element (the last of the four to be in direct physical...