Judging Key Requirements

To strike a key down prohibits the sense of its requirements. Clearly, if you really knock a key down, this will inevitably prevent you from playing musically, since it prohibits your ability to judge how much force is required for the coloring of each note.
Question: How much energy must be applied to the key in order to achieve the desired outcome?
In addition, it also prohibits your ability to give the due acceleration of the key during descent which is necessary for good touch.
The fundamental principle of keyboard technique is that the fingers, hand and forearm operate together in synchronicity. One assumption that emerges from this underlying foundation is that if the wrist is low, this critical alignment of the fingers, hand and forearm is broken. Since the wrist is the fulcrum for the hand, it must remain firm. The wrist does change in height according to the situation, (higher for intervals and chords) but if alignment is to be preserved and the wrist can never be lower than level (meaning it cannot collapse)

Obviously, it is by means of the fingertip that you must depress the key into sound. Also it is obvious that your finger must therefore be exerted during the moment of key-depression. Moreover, there is practically no such thing as tone-production solely by exertion of the finger. It must always be finger exertion along with the hand and forearm as described in the Act of Touch.
Note: Theoretically, finger-exertion alone is a possibility as shown in "The Act of Touch", and finger-exertion with loose-lying hand may suffice to hold a note down once it is sounded. However, in actual practice it does not suffice to sound notes with certainty (even in the softest passage) on our modern piano. On this website the keyboard technique is primarily directed towards piano playing.