ACCELEROMETER, an instrument or device that measures acceleration. An accelerometer for measuring linear acceleration usually consists of a mass attached to a restraining spring, and free to move only in the direction of the spring’s axis, which is called the sensitive axis of the accclerometcr. The tcnsion of the spring and the mass are adjusted so that the displacement of the spring due to a force acting on the mass along the sensitive axis is directly proportional to the force and thus to the acceleration resulting from the force. This follows Newton’s second law of motion, F = ma, where F is the force, m the mass, and a the acceleration. An indicator operated by the mass enables the magnitude of the acceleration to be read off directly.

An angular accelerometer is similar in principle to a linear accelerometer. The mass in this case is usually a disk attached to a spiral spring, and the rotation of the mass caused by an angular acceleration is again used to operate an indicator from which the acceleration can be read off.

In testing automobiles, accelerometers are clamped to the dashboard in order to study the various vertical accelerations to which the vehicles are subjected. The pickup and braking power of automobiles, the side load on tires, and warious other vibrations are also studied with this instrument. Accelerometers have been used to measure the vibrations of the hulls of ships as well.

In seismology, a recording instrument called the accelerograph, which consists of several accelerometers, is used for measuring the acceleration, period of vibrations, and duration of the shock during an earthquake.

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