Hila Science Camp - hilaroad.com

Speed of Sound


Here is a novel way to calculate the speed of sound.

We "clapped" two wooden boards together and recorded the event from a distance of 100 meters with a digital video camera.
A digital video camera captures video at a rate of 30 frames per second.  Analyzing the video on a computer we could "see" when the clap occurred and the audio part of the file showed when the sound arrived at the camera.
Each frame represents 1/30th of a second.  Counting the frames between seeing the clap and hearing the clap we know how long it took the sound to travel 100 meters.

In the images above you can see the boards moving quickly towards one another (they appear blurred). At frame 19 they clap together. The audio file underneath shows the sound that accompanies the video. The sound does not arrive at the camera until frame 28.

In our example we calculated the speed of sound in air to be 333.3 meters per second. The speed of sound varies with air temperature, the temperature during this experiment was 28 degrees Celsius, the speed of sound in air at this temperature is 348 m/sec.
Our calculation was close.  To improve results we could use a larger distance, 500 meters would give more time intervals to work with.
Some video cameras will capture at different frame rates. A higher frame rate would improve accuracy.

Link to Speed of Sound Calculator

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