The Effect of Temperature on the Speed of Sound

Research Questions:

• How quickly does sound travel?
• How does temperature affect the speed of sound?

The speed of sound depends on how dense the material that it travels through is. You know that cool air is denser than hot air, but does that mean that sound actually travels more quickly in cool temperatures than in hot temperatures? Figure it out with this experiment.

Material:

• Large building
• Metal pipe
• Hammer
• Partner
• Metronome
• Measuring tape
• Outdoor thermometer

Experimental Procedure:

1. Stand about 100 yards away from a large building. Bang on the metal pipe and listen for the echo. If you cannot hear it, try standing closer to the building, or find another building.
2. Tap out a beat on the pipe, still listening for the echo.
3. Slow down or speed up so that each tap on the pipe comes at the exact time as the echo from the previous tap. If you are doing this correctly, you should not hear the echo at all.
4. While you tap, your partner should turn on the metronome and try to adjust the frequency so that it matches the rate of your tapping.
5. Look at the metronome to figure out how many beats per minute you are tapping. Record this information.
6. Measure the exactly distance between you and the building that is creating the echo. Multiply this distance by two to get the distance that the tapping sound traveled.
7. Calculate how long it took for the tapping sound to travel back and forth by dividing 60 seconds by the frequency. (The frequency should be in beats per minute.)
8. Calculate the speed of sound by dividing the speed that the sound traveled (from Step 6) by how long it took to travel that distance (from Step 7).
9. Record the outdoor temperature that day.
10. Repeat this experiment on days that have very different temperatures. You may also want to try it at different times of the day, since it is cooler in the morning and evening and warmer in the middle of the day.

Terms/Concepts:  What affects the speed of sound? ;  What makes an echo?;  What is the density of cold air? Of hot air?

References:

First Place Science Fair Projects for Inquisitive Kids, by Elizabeth Snoke Harris. Pp. 74-75.