Smartphones have become widespread, and students carry them every day into the classroom. This pocket-size computer packed with sensors can contribute to an improved teaching of physics.1 In this experiment, making use of its portability and camera features, we suggest the use of a moving smartphone camera and subsequent video analysis2,3 to help the students see the world via the eyes of a moving observer and assess trends in position, velocity, and acceleration as a function of time.

The experiment consists of setting two carts in parallel motion and filming the movements, simultaneously with a fixed smartphone and with a moving smartphone riding along one of the carts (Fig. 1).

The video is processed in a computer, using Tracker,4 or with a smartphone, using VidAnalysis.5 To perform the video analysis, one needs to set the orientation and the origin of the reference axes. In addition,...

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