Collecting data with a mobile phone: Studies of mechanical laws such as energy and momentum conservation

TL;DR

This study demonstrates how students can use mobile phone videos to analyze mechanical laws like energy and momentum conservation through collision experiments, providing an accessible and visual learning experience.

Contribution

The paper introduces a method for studying mechanical laws using mobile phone videos and free software, enabling practical physics experiments without specialized equipment.

Findings

Data supports conservation of energy and momentum during collisions

Students observe effects of slipping and frictional torque on motion

Method is accessible and applicable to various mechanical phenomena

Abstract

We use videos taken with a mobile phone to study conservation of energy, conservation of momentum, and the work-energy theorem by analyzing the collision of a cue ball and the eight ball. A video of the full time sequence, starting from before the cue ball is struck until well after the collision, is recorded with a mobile phone. The video is imported into Origin (free to teachers and students taking a class) [OriginLab Corporation, Origin, Version 2020 (OriginLab Corporation, Northampton, MA, USA, 2020)], where the coordinates of the balls are digitized frame-by-frame using the free Video Extractor app. From these data, the velocities are determined as a function of time and used to determine the energy and momentum of each ball. The data suggest that the balls slip through part of their motion when rotating at an angular velocity different than the rolling angular velocity, so angular momentum and frictional torque must be considered. Such experiments require no specialized equipment other than a device to take a video, and the act of digitizing the data provides the student with visual reinforcement of the physics. Experimentation by students outside of campus can be fun for them and provides a useful alternative to classes when in-lab experiments are not practical. Use of a mobile phone in this way is generally applicable to any other mechanical phenomena that involve motion.