Analysing motion by hand
Classroom Activity for 14-16
What the Activity is for
Although computer-mediated analysis may dominate your practical work, there is a case for a moderate amount of work close up with the data. For this purpose we recommend the use of offset tables and multiple-exposure photographs. These are simpler to deal with, away from the computer, where high-frame-rate digital cameras have more or less displaced this as a practical measurement technique. Nevertheless, we'd encourage you to demonstrate such an image being made in the laboratory, as perhaps the most direct and simple way to explain how such images come to be.
There is also a physical immediacy to the multiple-exposure photographs, as they present a trace of the motion, visible all at once, so making strong links with the graphical representation that is missing from the step-by-step presentation of the data when using video clips.
What to Prepare
- a ruler
- a pencil
- a rubber
- some printed prepared grids (see below)
What Happens During this Activity
Introduce the multiple-exposure photographs, perhaps by putting an impressive one on a large screen. Talk through how these tell a story of the motion, and how students could tell the speed between any two (selected) points.
Show the image they are to work on, and bring to their attention the essential scaling factors that connect this representation to the original phenomenon (a measure of length on the image and the interval between the images).
Now introduce the offset sheets, making clear which columns are for the data, and which calculated. Finally set the challenge of producing good displacement–time and velocity–time graphs from the data.
This will be time-consuming, and you'll need to check with your mathematics-teaching colleagues, to see what their graph-plotting skills are like. It's probable that extracting and processing the data are the key activities here, so you may wish to use computational support for the plotting phase. However, we'd not recommend using a spreadsheet to process the data unless you can reproduce the offset cells of the support sheet. We think that these are important to keep track of the intervals.
Download the support sheet / student worksheet for this activity.