Measuring the speed of sound using echoes
Practical Activity for 14-16
Echoes are used outdoors to estimate the speed of sound. Good weather has to be ordered at the same time as the equipment!
Apparatus and Materials
- Large reflecting surface, preferably outdoors
Health & Safety and Technical Notes
Read our standard health & safety guidance
Obviously, you want strong echoes from one reflecting surface and not several!
- The experimenter stands as far away as possible from a large reflecting wall and claps their hands rapidly at a regular rate.
- This rate is adjusted until each clap just coincides with the return of an echo of its predecessor, or until clap and echo are heard as equally spaced.
- Use a stopwatch to find the time between claps, t. Make a rough measurement of distance to the wall, s. Thus the speed of sound, v = 2 s/t in the first case.
- Students are far more likely to grasp and to remember how to get the estimated speed of sound if you can arrange for them to undertake this experiment in pairs.
- Newton used echoes to estimate the speed of sound, in an outdoor corridor at Trinity College, Cambridge. It is alleged that the sound he produced was able to lift a door knocker at the far end of the corridor.
- Discuss why a
roughmeasurement of the distance is adequate.
This experiment was safety-tested in July 2006