Invisible Runner

An observer sees a sprinter hidden behind another sprinter four lanes away. He or she models a problem using similar triangles and proportions. This leads to an understanding of how much faster the outside lane runner is traveling and to an estimation of the difference in finish times.

This is a straightforward application of similar triangles, but it requires the students to do some research to gather data and some thinking to figure out how to model the problem. The results are cool in the sense that they show math in action where you may not expect to find it.