After an overview of dimensions and units conversions, we moved to one-dimensional motion. London golds earned by Missy Franklin in the 200-m backstroke and Usain Bolt in the 100-m sprint made for good examples of approximately one-dimensional motion. When it came time to analyze motion more carefully, however, I knew I had to use RGIII. His 40-yard dash at the 2012 NFL Scouting Combine fit perfectly with what I wanted to do (click here for video of his sprint): essentially one-dimensional motion using an athlete my students wanted to see.
The video I used was taken at 24 frames per second. I went frame by frame and recorded RGIII's time at each yard marker. The graph below is the result of that effort (click on the image for a larger view).
Each red data point is my best estimate of when RGIII's torso passed each yard marker (I converted yards to feet for the plot). The blue curve is a best-fit function that helps smooth the way for time derivatives, such as RGIII's velocity, which I show below (click on the image for a larger view).
The video claims that RGIII completed the sprint in 4.38 s with a top speed of 24.6 mph (39.6 kph). Given my admittedly rough estimations of where RGIII's torso was at each yard marker, all of which were angled from the camera view, I found that he completed the sprint in just over 4.37 s with a top speed of 23.2 mph (37.3 kph). The NFL was certainly using more accurate timing devices, but I'm happy with how close I got. RGIII's time and top speed are incredible! Check out his acceleration below (click on the image for a larger view).
I have scaled his acceleration by the acceleration due to gravity. Note that he explodes off the starting line with more than two g's!
When I began Physics of Sports, I was not planning to look at RGIII in the first week. Letting students help decide what to cover in a sports physics course means that I get to learn things I wasn't expecting to learn. RGIII certainly made for a fun first sporting example to analyze in detail.