The purpose of this paper is to demonstrate how the Doppler effect can be analysed to deduce
information about a moving source of sound waves. Specifically, we find the speed of a car and the
distance of its closest approach to an observer using sound recordings from smartphones. A key focus
of this paper is how this can be achieved in a classroom, both theoretically and experimentally, to
deepen students’ understanding of the Doppler effect. Included are our own experimental data (48
sound recordings) to allow others to reproduce the analysis, if they cannot repeat the whole
experiment themselves. In addition to its educational purpose, this paper examines the percentage
errors in our results. This enabled us to determine sources of error, allowing those conducting
similar future investigations to optimize their accuracy.