How Does the Speed of Sound Vary with Altitude?
The payload experiment, created using a 3D printerCopyright 2021 Trina Kilty, University of Wyoming
Understanding the layers of the atmosphere and their effects on aerospace designs helps engineers design explore the skies—and beyond! In this activity, students make sense of and use real world data to investigate a variety of phenomena including the speed of sound, waves, air pressure, humidity, and temperature at high altitude. Using data collected with payload sensors attached to a high-altitude balloon students examine, interpret, verify theoretical speed of sound equations. By graphing these data against other measurements such as air pressure, humidity, and temperature, students conclude that the speed of sound varies as a function of temperature, but not air pressure and humidity. Moreover, students determine that the speed of sound data loses accuracy at high altitude and low temperature, highlighting limitations of the data and challenges that engineers face when designing an experiment.
To design aircraft, rockets, and sensors, an engineer must know the characteristics of the atmosphere where these devices operate. Properties such as temperature, pressure, and density depend on altitude. For example, two properties which determine how an aircraft wing will perform are density and speed of sound. These two characteristics also lead to design tradeoffs. Measuring how the speed of sound varies with altitude and what factors cause or contribute to its variation gives an engineer valuable design information. When engineers get information from measurements, they must critically examine the data to assure that it measures what they are trying to measure (also known as validity) and also determine its accuracy.
After this activity, students should be able to:
- Explain how sound functions and how to measure changes in the speed of sound.
- Describe changes in real-world data and how it affects design and graph relationships of independent and dependent variables.
- Verify a scientific claim by examining evidence of relationships of data (graphs).