How do accelerometers measure changes in a vehicle’s velocity?

Accelerometers do not measure velocity directly; rather, they measure the rate at which an object's velocity changes, which is defined as acceleration.1

In a vehicle, an accelerometer functions by measuring the force exerted on a reference mass held within the device. Because acceleration cannot be measured directly, the instrument utilizes Newton’s second law—force equals mass times acceleration—to compute the value. As the vehicle accelerates, inertia causes a suspended mass inside the accelerometer to lag behind the housing. This displacement is proportional to the vehicle's acceleration and is converted into an electrical signal.1

In inertial guidance systems, these acceleration measurements are sent to a computer. The computer performs numerical integration on the acceleration data to calculate the vehicle's current velocity. By performing a second integration on that velocity data, the system can further determine the vehicle's current position.2