Abstract

The speed of sound in an ideal gas depends on the temperature, the average mass of the gas molecules, and the adiabatic index. All three of these variables change during a high-altitude balloon flight. In particular, the drastic temperature changes cause variations of the speed of sound in excess of 10%, which are easily measurable with low-cost ultrasonic range finder. These sensors consist of a speaker that emits short bursts of sound waves, and a microphone that listens for an echo from a reflection off a nearby object. A microcontroller measures the time it takes for the sound waves to return to the sensor. Using this measured travel time and estimations of the speed of sound in air, ultrasonic sensors are commonly used to measure distances in robotics applications. We will present an experiment in which we mount an ultrasonic sensor inside a payload pod to measure the speed of sound during a balloon flight. Because the physics of sound waves is an important part of the introductory physics sequences at most universities, this experiment provides a rich context for integrating high-altitude ballooning into the curriculum.

How to Cite:

Jabon, D. & Beck-Winchatz, B., (2012) “Measuring the Speed of Sound with an Ultrasonic Range Finder David”, Academic High Altitude Conference 2012(1), 109–113. doi: https://doi.org//ahac.8335