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Speed of Sound

You can measure the speed of sound the same way you measure the speed of a runner, with a stopwatch on a closed track.

• Find a place where you can hear a good echo, and stand a known distance from whatever the sound is reflecting off of.
• Fire a starter's pistol and start the stopwatch. Stop the watch when you hear the echo.
• Divide 2 times the distance (it's a round trip) by the time to get the speed.

At 21 degrees C (70°F), you should get 344 meters per second, or 1129 ft per second. At freezing, the numbers are 331 m/s or 1087 ft/s. The proper formula for the change in speed due to temperature is:

Where T is degrees Celsius. The works out to about a 0.1% change per degree Fahrenheit.

The Speed of sound in water is 1480 m/s or 4856 ft/s. More than 3000 miles per hour.

There is a project under way to take the earth's temperature by measuring the speed of sound between the USA and Australia.

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