- 1 hammer
- something hard and resonant (and inanimate) to bang it on
- 1 clock with a second hand
- 1 measuring tape
- 1 helper
- 1 pair of binoculars
Sound travels at 344 metres per second in air at 20 °C. This is slow enough for noises to be noticeably delayed when heard from even quite a short distance. You can use this effect to measure the speed of sound.
Ask your helper to a hit a wall or a piece of metal repeatedly with the hammer, about twice every second. The exact frequency of the beat doesn't matter; it can be measured later. But the beat should be regular.
Now start walking away, looking back from time to time to watch your helper pounding away as you listen to the sound of their hammering. As the distance increases, the delay after each beat before the sound arrives will become longer and longer.
Eventually the delay ...
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