Speed of sound

I showed this to the kids the other day when trying to find clips to reinforce the idea of speed of sound vs speed of light. The kids got the idea pretty clearly and we followed it with a few measurements of the speed of sound using echos off the school building across the rugby field.  I think its good as an intro as its pretty dramatic and not a subtle observation. The experiment is great as the kids love getting within only 50 m/s of the true value just from a few stop clocks and wooden blocks smacked together.