Jared Owen created a fantastic video explaining the mechanics of a grand piano.
This video covers the different parts of a Grand Piano and what happens when a key is pressed.
For those interested - the keys being played on the piano are the real keys for the song (or at least close to it).
This part covers the three foot pedals and how they change the sound of the grand piano. We'll build off of part 1 and show you how the mechanism works inside the piano. Keep in mind that this video only covers the grand piano - the upright piano works differently.