The Speed of Sound Demo

P115/P116 Laboratory Demonstration #15

Summary:

* Three different demonstrations to measure the speed of sound
* The purpose of these demonstrations is to help the students achieve a good feel for the concept of the speed of sound by understanding the methods by which it is measured.

You can click on the image to download it in gif format.

Further information on Theory, Apparatus, Procedure, and Helpful Hints is available. The equipment for this demo is stored in Rockefeller rooms 302 and 302B.

Theory

Sound is a wave. It travels by propagating through air molecules. As such, the speed of sound in air depends on the average speed of the air molecules through which it is traveling. This speed in turn depends on the temperature and humidity of the air.

Apparatus

The equipment needed for this demo is:

* two microphones
* a computer with timing software
* a two meter stick
* two objects to beat together to make a sharp sound
* a cap gun may be used with a video camera

Procedure

Procedure (1) Set the two microphones a certain distance from one another. Beat two objects that will give a nice tap with a few echoes between them. The difference in the distance between the microphones and the clicking objects represents the distance the sound travelled, and the timing software under Utilities on CYPRESS or in the E: drive can be used to measure the time it took the sound to travel the distance.

Procedure (2) Set one microphone facing the blackboard or a wall. The distance between the beat objects (trapped between the microphone and the wall) is the distance the sound travelled.

Procedure (3) If there is a thunderstorm, have students count the time between the flashes of lightning and the thunder. Otherwise, take them outside and have several of them line up a given distance apart. Tell them to raise their hand when they hear a noise created by another student at the end of the line. Optionally, videotape the line. Note that the students must be spread over quite a distance for this to work, at least the length of a football field. Only a few students with good reactions should be used for this demonstration.

Helpful Hints

Sorry- no hints at this time.

To return to the Heat Sound & Light Demo Catalogue .





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