Piezoelectricity
The phenomenon in which certain materials generate electric charge under mechanical stress and deform when voltage is applied. It is used in sensors, igniters, and ultrasonic transducers.
Lightning defied explanation for a century. Colliding ice grains separate charge, but symmetric ice makes no electricity when pressed — piezoelectricity fails. In 2025, bending ice was shown to break symmetry and generate it: flexoelectricity.
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