Anyone who has been on the planet for any length of time knows that body weight changes. And we are not always happy about that!
Body weight changes slowly, over a period of time. It does not change in a matter of moments or from one measure of music to the next. For this reason, it is not possible to change body weight to change the sound produced by the piano. We can't make an arm weigh more or less in the blink of an eye.
Heretical? Counter to everything you've ever been taught about piano technique? Stand next to me. Over the course of my ever-lengthening career as pianist and teacher, I've been given the advice to use arm weight many times. And I taught this concept many times, until.....
I met Chris Stevens, a British Alexander Technique (AT) Teacher and physicist. He was on a mission to prove the merits of AT under laboratory conditions. He observed people going from sitting to standing while measuring the effort exerted on a force plate. He observed himself in movement by inserting wires into his leg muscles. He was affable, and he was serious about his work.
As I sat on a soft leather sofa, drinking wine and chatting with Chris and other AT teachers after an all-day workshop, I took the opportunity to ask many questions. When it came to the subject of weight at the piano, he simply said, "it is not possible to put weight into the piano keys". And who was I, a would-be AT teacher without a physics degree, to argue?
I took this idea back to the piano, back to my teaching, and back to the drawing board. More questions, more answers, and eventually a return to basic physics. Sit back on your comfy sofa, and follow my exploration.