Determine the Speed of Sound

5 Steps

Step 5: Really precise stopwatch

Now we can easily see the recording of our snap and the echo of our snap. All we need to do now is determine how long it took the sound to travel from the mouth of the tube to the floor and back again.

The easiest way (as pointed out by one of my students) is to click and drag from the beginning of the sound to the beginning of the echo. If you look near the bottom of the window you'll be able to see how much time you've highlighted.

For mine I get a time of 0.009057 seconds. I figure four significant figures is pretty good. Now I simply measure the length of my tube, which in this case was 1.548 m. Since the sound has to go there and back again I double this distance (almost everyone forgets to do this the first time).

Speed can be calculated by dividing distance by time.

So v = d/t; v = 3.096/0.009057

v = 341.8 m/s or 764.6 mph

The accepted value at sea level is 340.29 m/s (the value in my classroom can be anywhere between 340 m/s and about 348 m/s depending on the weather).
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llanyort says: Jun 18, 2009. 1:18 PM
question(s) - 1)what if you wanted to measure the distance from the object(that created the sound) to the microphone that captured the sound ? 2)what if you placed two or three other microphones in the room in each corner, could you use them as well ? or would they cause any foreseeable problems in this project ? Im trying to pinpoint the distance and vector of an orignating sound. Is this possible ?
falconphysics (author) in reply to llanyortJun 18, 2009. 2:12 PM
I've not tried using multiple microphones with Audacity before. I'm not sure you could do that. What you could do would be to wire two mono microphones to the stereo input and record as a stereo track though.
llanyort in reply to falconphysicsJun 23, 2009. 8:03 AM
thats a good idea !!! thanks.. :-)