Home Experiment #70 H. A. Daw 30 June 1993



File: SOUNDR.DOC

SOUND RANGING

BACKGROUND

Anybody who has watched a band playing at half-time at a football game knows that sound has a relatively slow velocity. There is an easily decerable lag between the time you see a drummer hit a drum and the time that you hear the sound. In this experiment you will use that finite velocity to estimate the distance to a lighting strike. Of course this experiment depends on the cooperation of the weather to provide a thunder storm. Hence the experiment will be assigned early in the semester and the reports collected at the end.

References

1. Crummet, W. P. and Western, A. B., University Physics (Modes and applications), (Wn. C. Brown, Publishers, Dubuque, IA, 1994) pp 452-455.

2. Hewitt, P.G. Conceptual Physics, 7th Ed., (Harper Collins College Publishers, 1993) pp 342.

3. Ostdick, V. S. and Bord, D. J., Inquiry Into Physics, 2nd Ed., (West Publishing Company, St. Paul, MN, 1991) pp 249-258.

4. Serway, R., Principles of Physics, (Saunders College Publishing NY, 1992) pp 643-645.

5. Tipler, P.A., Physics, 3rd Ed., (Worth Publishers Inc., NY, 1991) pp 439-442.

6. Young, H.D., Physics, 8th Ed., (Addison Wesley, NY, 1992) pp 549-553.

Materials

Stopwatch

Instructions

This experiment will require the cooperation of the weather and therefore should be planned to be flexible. At a time when lightning is occurring, measure the time between the flash of a lightning bolt and the time the sound of thunder arrives. If the time is extremely short, i.e. instantaneous, the lightning is dangerously close. In general the time will be several seconds. If there is a lot of lightning it may be difficult figuring out which lightning strike goes with which thunder. If the lightning strike covers a lot of the sky, and takes a few seconds itself, it may be difficult to know which area the thunder comes from. However, the first thunder to arrive comes from the nearest distance. If the lightning is far away, no thunder may be heard.

Let us assume that there are some discrete lightning strikes that are close enough to you so that one can hear the thunder. Measure the time from strike to thunder. Since sound travels at about 1087 feet per second or 331.3 meters per second at 0C, the distance to the lightning can be determined by multiplying the time for the sound travel (thunder) by the speed of sound in air. Distances of 1 or 2 miles are easily determined, but larger distances are capable of being determined.

Safety: A number of people are killed each year by lightning. Therefore do not put yourself in jeopardy for this experiment. It can be carried out in your room by looking out the window. It should be carried out under a sheltered porch. It should be carried out from inside a parked car. But do not stand outside in a exposed area.

Even if you do not have your stopwatch with you when you come upon a thunderstorm, you can still do the experiment. By repeating the phrase “one thousand one, one thousand two, ...” at a normal speaking pace you can fairly accurately count off an interval in seconds.

Report

The report can consist of several range measurements. The range measurements should be accompanied by an estimate of the uncertainty in the range.

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