Accelerometers can also be used to measure G-forces.
How it works.
Plate B is in this case suspended between plate A and plate C. While stationary or while not accelerating or decelerating (maintaining a constant speed), plate B is equidistant from the two outer plates. When a car accelerates or an aircraft pulls up sharply plate B will shift closer to one of the other 2 plates. One example of an accelerometer uses electricity flow to measure acceleration, as plate B nears A or C then the electricity flow will gradually increase also.
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A B C
Source: http://www.vericomcomputers.com/HowItWorks.htm