The physical or key aspect of Technique

Tone-production:

1. The more speed in the string, the louder the resultant sound. Only by making the key (and the piano string) move quickly are you able to increase the volume. There is no other way.
2. The piano key is a leverage system^[1], a machine to enable you to get speed with the string, and to ensure dynamic control of the exact speed (or tone) desired.
3. Open your piano lid and observe the hammerheads. Now put a finger upon a key, and notice, when you depress the key 3/8 of an inch the hammer-head moves about five times that distance. Hence the leverage system of the piano multiplies your motion by five times, the speed with which you depress the key.
4. Now notice that the hammer returns back the instant it has reached the string and has set the string into vibration (or movement) even though you may be keeping the key depressed afterwards. This is the result of the hopper device, which allows the hammer to rebound from the string. Without such a device the hammer would be jammed against the string, and tone would not be able to resonate.
5. Note also, that as you put the key down you are lifting the damper away from its strings, thus leaving them free to continue sounding; and that the damper returns to the strings when you allow the key to come up again, thus arresting (or "damping") the sound.
6. The "Grand" action also includes a device (the "repetition lever") which enables you to re-sound the note, without having to allow the key to rise fully, about an eighth of an inch should suffice. The action is also provided with a "check," which brings the hammer to rest after it has fallen back from the string, so as to prevent its rebounding and re-striking the string on its own, and thus spoiling the tone.

[1]leverage system: A lever is a rigid body capable of rotating on a point on itself. On the basis of the locations of fulcrum, load and effort, the lever is divided into three types. Also a leverage is a mechanical advantage gained in a mechanical system.