The goal of this unit is to show you how to develop an incredibly controlled dynamic range at the piano - from the softest pianissimo to the most thundering fortissimo, all without generating tension, losing control, or creating an "ugly sound".
Any change in dynamics at the keyboard means changing the rate at which you accelerate the key descent.
Anyone can "push hard" and get a loud sound. The question for piano technique is can you accelerate the key with incredible control, and without generating tension.
In more complex technical patterns, it would be nearly impossible to detail all of the elements of movement that go into creating a louder or softer sound (a quicker or slower key descent) but an excellent way to gain this sort of control is by first understanding all of the basic ways a single key (or group of keys simultaneously) can be depressed.
This is an extended section, and while it may seem to be somewhat tedious in detail, I would invite you to carefully work through each of the motions described. You will find that they apply to a countless number of "real-world" piano situations, either alone or as parts of more complex motions.
By gaining a true control over these fundamental movements, you will be light-years ahead of almost all students of piano technique, and will slowly develop an incredible ability to control the piano's sound.