[1.IV.6.1] Momentum Theory of Piano Playing
Slow play in piano is called “playing in the static limit”. This means that when depressing a key, the force of the finger coming down is the main force used in the playing. As we speed up, we transition from the static limit to the momentum limit. This means that the momenta of the hand, arms, fingers, etc., begin to play important roles in depressing the keys. Of course, force is needed to depress the key, but when in the momentum limit, the force and motion can be out of phase, while in the static limit they are always exactly in phase. In the momentum limit, your finger is moving up when your finger muscles are trying to press it down! This happens at high speed because you had earlier lifted the finger so rapidly that you have to start depressing it on its way up so that you can reverse its action for the next strike. The actual motions are complex because you use the hand, arms, and body to impart and absorb the momenta. This is one of the reasons why the entire body gets involved in the playing, especially when playing fast or loud. Examples of situations where momenta are important are fast trills or tremolos, rapid repetitions or staccatos, and quiet hands play. The swing of the pendulum and the dribbling of the basketball are in the momentum limit, so that the momentum limit is a common occurrence. In piano playing, you are generally somewhere between the static and momentum limits with increasing tendency towards momentum limit with increasing speed.
The importance of momentum play is obvious; it involves many new finger/hand motions that are not needed in static play. Thus knowing which motions are of the static or the momentum type will go a long way towards understanding how to execute them and when to use them. Because momentum play has never been discussed in the literature until now, there is a vast area of piano play for which we have little understanding. Beyond mentioning the importance of momentum, I have little to present at this time. The only useful information to the pianist is that there is a transition from static play to momentum play as you speed up, so that in fast play, the technique will require entirely new skills that you didn’t need at slow play. In fast trills and the quiet hands play, the hand seems to be motionless, but it is not. It is making rapid adjustments in order to accommodate the momenta of the fast moving fingers, and we must learn to apply forces to the fingers that are not in phase with their motions. This is why practicing slow trills every day will not help you to play fast trills. PSs do a much better job because you can immediately start practicing the momentum mode.