A version of Buys Ballot experiment for quantitative proof of the Doppler effect in students' laboratory work, adapted to online conditions

There are many possible ways to experimentally test the Doppler effect. Last year's epidemic forced us to transform the laboratory practices for online conditions at university level physics education. We performed a similar experiment as Buys Ballot's and recorded it for student's online laboratory work: we placed a loud, single-frequency sound source on a moving car and recorded the sound near the road while the car was passing with constant speed. The source was a smartphone connected to a loudspeaker. The digital recording was then analyzed by students in the frame of online laboratory work using the "phyphox" application on their smartphones (but any other frequency analyzer app could have been used). A sample calculus for the speed of the car and the estimation of the errors of measurements is also presented. The scientific processing of a dataset is almost as useful for students as it would be for a laboratory experiment conducted in attendance education. The advantage here is that they could deal with a phenomenon which previously was not included among the laboratory themes, although it is interesting and has a large variety of applications. Highlighting the importance of the Doppler effect and the good practices in other countries, we recommend to include this topic in the Romanian high school physics curriculum as well.