Accelerometer

An accelerometer is a device that measures the proper acceleration of an object, meaning the acceleration of the object relative to an observer who is in free fall, rather than acceleration measured against a fixed coordinate system. An accelerometer resting on the surface of the Earth measures an acceleration due to gravity of about 9.81 meters per second squared pointing straight up, while an accelerometer in free fall reads zero acceleration. The device typically works by suspending a damped mass on a spring inside a frame. When the frame accelerates, the spring compresses or stretches to exert a force on the mass that counteracts the acceleration, and because spring force scales in direct proportion to how far it is compressed or stretched, measuring that displacement directly reveals the size of the acceleration. This description is adapted from Wikipedia contributors under CC BY-SA 4.0; changes were made. https://creativecommons.org/licenses/by-sa/4.0/