1. Different types of displacement and how to measure them

Since displacement can be defined as the variation of a position as a function of time, the first derivative of displacement with respect to time gives velocity, and the second derivative gives acceleration. These two quantities are certainly accessible from the signal supplied by a displacement transducer; however, it should be noted [1] that the signal-to-noise ratio is reduced when a derivative is derived with respect to time. It is therefore preferable to use sensors specifically designed to measure these quantities: linear or angular tachometers for speeds [2] , accelerometers or gyrometers for accelerations [3][4][5]