This paper describes how big distances in open areas can be calculated using the speed of sound and a pair of walkie-talkies. This low-cost experiment challenges the students to solve a very common problem and at the same time uses some basic concepts like the speed of sound and of electromagnetic waves. The idea was partly inspired during an outdoor activity with a group of students. The class was divided into two groups, each one working at opposite sides of a lake. We could see each other and communicate using walkie-talkies. Suddenly, a student asked: “How far away do you think they are?” After some guesses and suggesting ideas to find the answer, we realized that we could use walkie-talkies to solve the problem.

Topics
Speed of sound, Electromagnetism, Education
1.
GRAM software, by R.S. Horne, available at: http://www.visualizationsoftware.com/gram.html. Links to other commercial and freeware programs for audio spectrum analysis: http://www.visualizationsoftware.com/gram/links.html.
2.
E. Hecht, Physics: Algebra/Trig, 2nd ed. (Brooks/Cole, Pacific Grove, CA, 1997), p. 401.
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© 2005 American Association of Physics Teachers.
2005
American Association of Physics Teachers
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