How do accelerometers work and where are they applied?

Accelerometers measure acceleration using a proof mass on a spring. Acceleration causes mass displacement proportional to a = F/m. Sensing methods include: piezoelectric (wide frequency range, no DC response), piezoresistive (measures DC, shock measurement), capacitive (MEMS, low cost, includes DC), and servo (high accuracy, force-balance). Applications include: vibration monitoring (machinery health), motion sensing (mobile devices), inertial navigation, crash detection (airbags), and seismic monitoring. Key specifications are sensitivity, frequency range, resolution, and shock survival.