An accelerometer is a device that measures the vibration, or acceleration of motion of a structure. They measure in meters per second squared (m/s2) or in G-forces (g). The force caused by vibration or an acceleration (change in motion) causes the mass to "squeeze" the piezoelectric material which produces an electrical charge that is proportional to the force exerted upon it. Since the charge is proportional to the force, and the mass is a constant, then the charge is also proportional to the acceleration. Accelerometers are useful for sensing vibrations in systems or for orientation applications.