AN ULTRASONIC DOPPLER SYSTEM FOR THE STUDY OF THE LAW OF FREELY FALLING BODIES

A novel method is reported for the experimental verification of the law of motion of freely falling bodies using a simple and inexpensive ultrasonic air Doppler technique. The system employs a resonant-type piezoelectric transducer as a transmitter of ultrasound (frequency 32.8 kHz) and a wide-band electrostatic transducer as a receiver. Its distinguishing feature is that instantaneous velocity is measured instead of time of fall. It has been shown that the values of instantaneous velocity of a falling steel ball measured experimentally and the values calculated from the relation V(cal) = square-root (2gS) are in close agreement. The system is likely to be useful as a demonstration experiment in teaching institutions.