Motion Detector
This is no substitute for being able to do this in real life, but the sketch allows the user to play with a walker and a motion detector (like a CBR) that then graphs time vs distance. The sketch is preloaded with a few graphs to try and duplicate. A lot of the benefit of this task is describing what you did to make the graph, so don't skimp on the conversation or writing!
More GeoGebra at bit.ly/mh-ggb