How do accelerometers detect movement?

• A. By measuring wind velocity
• B. By measuring the forces from acceleration of mass
• C. By GPS signals
• D. By counting engine revolutions

Answer: (B)

Accelerometers detect movement by sensing the inertial force on a tiny mass inside the sensor. When the device accelerates, that mass tends to resist the change in motion, so it pushes against the sensor’s support structure. This deflection of the internal mass is measured by the sensing element (often a suspended proof mass with capacitive plates in MEMS devices or a piezoelectric readout) and converted into an electrical signal proportional to the acceleration along each axis. Gravity is just a constant acceleration when stationary, which the sensor can separate from dynamic motion in multi-axis designs. This is different from wind velocity, GPS signals, or engine RPM, which don’t measure the internal inertial response that defines accelerometers.