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.
