Using a digital camera to study motion
Andrew McNeil, Daniel Steven · School science review · 2006
A digital camera can easily be used to make a video record of a range of motions and interactions of objects - shm, free-fall and collisions, both elastic and inelastic. The video record allows measurements of displacement and time, and hence calculation of velocities, and practice with the standard formulas for motions and collisions. The camera extends the range of motions that can be studied, to include free-fall with forward motion and collisions between two moving objects. The exercise gives students valuable experience in handling raw data, and brings a concrete experience to a part of physics that is sometimes treated theoretically. Some of our earliest conscious interactions with the physical world involve forces on objects, and their consequent motion. As children, we soon become skilled at applying just the right force for just the right duration to produce the desired motion. Galileo's study of the motion of balls rolling down slopes was one of the earliest mathematical analyses of terrestrial motion (Gribbin, 2002: 101). Yet motion remains difficult to observe and quantify. Ticker-timers, light gates and motion sensors of various types will continue to be useful. This article describes how we have used a digital camera to record and analyse motion in various situations, as part of an A-level physics course. The camera used was an Olympus C360Z. This records video in Quicktime format, at 15 frames per second (fps) with a frame size of 320 x 240 pixels, giving a reasonable degree of resolution, sufficient to measure the position of a pointer to the nearest centimetre. The video can be viewed frame by frame, using Olympus or Apple software. The file sizes are quite small, being about 0.3 MB for every 1 second (15 frames) of video. The photographs in this article show selected frames from the video record taken in lessons, and hence show other features like lab taps, and what was on display boards at the time. The video frames have been augmented in Microsoft Word, with the addition of features such as scales and dimensions. The work described here was triggered by the demise of our department's last BBC 'B' computer, and also by one of us (AJM) discovering the delights and power of digital photography. When we found out how easy it was to analyse the simple harmonic motion (shm) of a mass oscillating on a spring, we went on to look at projectiles and collisions.