Home >> Science & Nature >> Science

Does an Accelerometer Measure G-Force?

An accelerometer is a device that measures forces due to acceleration. It also measures gravity, or G-force, which is a phenomenon related to acceleration; in fact, an accelerometer employs units expressed in terms of gravitational strength. Some accelerometers are purely mechanical, others are electromechanical. Recent advances have led to inexpensive miniature devices in cell phones, cars and other consumer goods.

Second Law of Motion
- Newton̵7;s Second Law of Motion equates mechanical force with mass multiplied by acceleration, which is a steadily increasing speed. An increase in force happens only by increasing an object̵7;s mass or acceleration. An accelerometer measures the force acting on an object of fixed mass. If the force on the object is zero, the object is still or moving at a constant speed; increasing force means an increasing acceleration. A decrease in speed is negative acceleration, or deceleration.
Gravity and G-Force
- The force of gravity produces a downward acceleration in all objects near the Earth. Even non-moving objects experience this downward force. A dropped object accelerates towards the Earth with the same acceleration regardless of the object̵7;s size or weight. For convenience, engineers established the ̶0;G̶1; unit to measure gravity, where one "G" is the acceleration produced by Earth̵7;s gravity. Expressed in other terms, one G is 9.8 meters per second squared. An accelerometer, held so it measures motion forwards and backwards, measures no acceleration if you stand still. Turned so it measures up and down, it registers the force of gravity.
Technology
- Most accelerometers rely on measuring the force acceleration produces on a test mass. A laser accelerometer, for example, uses a mass to deflect a straight beam of light; the greater the acceleration, the greater the deflection. A light sensor detects the laser, measuring its movement. A technology called Micro Electro Mechanical Systems produces tiny mechanical systems on silicon microchips. Here, a sensor consists of a miniature mass surrounded by capacitive material; in either case, the force from acceleration presses the mass against the material, changing its electrical capacitance. MEMS-based accelerometers are reliable, much smaller and less expensive than earlier examples.
Applications
- Many smartphones now have accelerometers built into them; using the device, the smartphone measures gravity, automatically flipping its display from portrait to landscape mode when you turn it, for example. Video game controllers use miniature accelerometers to sense a player̵7;s hand movements. In vehicles, accelerometers feed data to stability-control systems; if one accelerometer judges ̶0;up̶1; and ̶0;down̶1; by measuring gravity and its signals have suddenly reversed, the car has rolled over. In this case, a computer automatically shuts off the engine and calls an emergency responder.

Science