Acoustic determination of g by tracking a free-falling body using a smartphone as a sonar

The gravitational constant is determined by tracking the movement of a free-falling body in an aluminium pipe. For this purpose, a smartphone is used to generate sound waves of a specific frequency and to simultaneously detect the sound wave resonances in the tube. The ability of smartphones to generate and receive the sound waves to track a moving body, like a ‘submarine SONAR’ does, is an essential point in this work. Concepts of kinematics and acoustics are combined to determine the gravitational acceleration within 1% when the result is compared with the reported value.