Accelerometer

An accelerometer is a sensor that measures proper acceleration along one or more axes. Its output includes effects of gravity, distinguishing it from a device that measures coordinate acceleration alone.

Proof mass: A movable mass whose displacement or force response provides a physical measurement signal. In many accelerometers, inertial force on this mass is the quantity the sensor detects.
Proper acceleration: Acceleration measured relative to a freely falling frame, including the support force felt by an observer. It is the physical quantity an accelerometer measures, rather than coordinate acceleration.
Inertial navigation system: A navigation system that estimates motion and position from inertial sensors without external references. Accelerometers provide its measured specific force for estimating changes in velocity.
Gyroscope: A sensor that measures angular velocity or changes in orientation. It measures rotation rather than linear specific force, complementing accelerometer data.
Capacitive sensing: A measurement technique that detects changes in electrical capacitance between conductors. Many MEMS accelerometers infer proof-mass motion from changing capacitance.
Specific force: Non-gravitational force per unit mass acting on an object. Accelerometer readings are commonly modeled as specific force along the sensor axes.
Inertial measurement unit: An instrument combining accelerometers and gyroscopes to measure motion and orientation. It pairs acceleration measurements with angular-rate measurements for three-dimensional motion sensing.
Magnetometer: An instrument that measures the strength and direction of magnetic fields. It provides a heading reference that acceleration measurements cannot supply.
Piezoresistive effect: A change in a material's electrical resistance caused by mechanical strain. Some accelerometers convert strain in a flexure into a resistance change.
Equivalence principle: The principle that local effects of gravity are indistinguishable from those of acceleration. It explains why a stationary accelerometer registers gravity while one in free fall reads near zero.

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