Hot Potato, Cool Foil
Figure 1. An artist's conception of the shuttle re-entering the atmosphere. Friction with the air causes the shuttle's outer surface to heat substantially.Copyright 2008 National Aeronautics and Space Administration http://www.nasa.gov/centers/ames/multimedia/images/2006/shuttlehistory.html
Students explore material properties by applying some basic principles of heat transfer. They use calorimeters to determine the specific heat of three substances: aluminum, copper and another of their choice. Each substance is cooled in a freezer and then placed in the calorimeter. The temperature change of the water and the substance are used in heat transfer equations to determine the specific heat of each substance. The students compare their calculated values with tabulated data.
All engineers must know the properties and tolerances of the materials they are using in a project, whether it be the reaction temperature in a chemical process, the strength of a composite material in airplanes, the steel in a bridge, or the temperature tolerances in an engine. In particular, NASA has to know the tolerances and properties of the materials engineers use to build space vehicles. The heat shield is a good example. Engineers have to be able to predict how much the heat shield will expand, how hot it will get, and how quickly it will wear down using the various material properties. Heat capacity is one of these important properties, and can be determined using basic knowledge of heat transfer.
After this activity, students should be able to:
- Explain that heat capacity is the amount of heat a quantity of a substance can absorb/release when changing by one unit temperature.
- Explain that material properties and tolerances are important in the design and construction of engineering projects in order to assure functionality and safety as well as exploit a substance's natural abilities to solve a problem.