Using a device that produces a repetitive sound and a visible pulse at the same instant
(e.g. metronome), have students walk away from it until the sound and visible
key are "in sync" again. Since speed is distance/time, divide the distance from the
signal producer by the time interval between the two pulses to calculate the speed of sound.
(Remind students that we are assuming that the speed of light is such that the light pulse travels
to the students "instantaneously.")
Here's a mpeg video that can be used. Set up a computer/laptop with speakers set at full volume.
speed-of-sound-video.mpg (3.18 MB). Be sure to save the file to your computer, then
play that file instead of trying to run it off the internet ("right click" and "Save link as..." to
download the file).
The video has a tone and picture every second. The clip is ten seconds long, so have your media player
set to automatically repeat the clip endlessly.