What device is used to measure changes in speed or direction along the axis in which they lie?

The accelerometer is a device specifically designed to measure changes in speed or direction of movement along one or more axes. It detects the acceleration it experiences relative to free fall, providing data on how fast an object is speeding up or slowing down in a specific direction. This measurement is essential in various applications, including smartphones, cars, and aerospace technology, where understanding changes in motion is crucial for navigation and stability.

In contrast, other devices such as a gyroscope measure the orientation or angular velocity rather than linear acceleration, while a barometer measures atmospheric pressure, and a magnetometer assesses magnetic fields. Each of these devices serves distinct purposes in their respective fields, but they do not fulfill the role of measuring linear changes in speed or direction along an axis like an accelerometer does.