Which device measures the velocity, rotation, and shaking of a mobile device?

The correct answer is the accelerometer. This device is primarily designed to measure the acceleration of the mobile device in one or multiple axes, which includes its speed and orientation relative to gravity. The accelerometer detects changes in velocity and movement, allowing it to register when the device is tilted or shaken. This functionality is crucial for various applications, such as enabling automatic screen rotation and detecting the positioning of the device in space.

The gyroscope, while closely related, specifically measures rotational movement and the device's orientation in 3D space. It is often used in conjunction with an accelerometer to provide more precise motion tracking, but it does not measure linear acceleration or shaking to the extent that an accelerometer does.

The trackpad is an input device used for pointer navigation and does not measure motion in the context of a mobile device's movement attributes. The digitizer refers to a technology that converts analog touch inputs into digital signals and is primarily associated with touchscreen devices, rather than measuring movement or velocity.