Quartz crystal oscillators make use of the piezoelectric effect. Do they not qualify as solid state? For that matter, capacitor whine is due to electrically ind

Quartz crystal oscillators make use of the piezoelectric effect. Do they not qualify as solid state? For that matter, capacitor whine is due to electrically induced mechanical vibration as well; I've never heard anyone claim they don't qualify as solid state components though. To me, moving parts generally refers to physically coupled but distinct pieces that move relative to one another. Otherwise heating anything that contained a piece of metal by a few degrees would disqualify it.