Education: Activities & Documents

Thermal Expansion
Activity 4.7: Thermal Expansion (p. 39-40; click here for videos accompanying this activity). A good grasp of the underlying principles of thermal physics is essential for understanding how the ocean functions and how it impacts climate. Thermal physics is one of the science subjects that students are familiar with and experience on a daily basis, but intertwined with the experiential knowledge they bring to class comes a mixed bag of misconceptions that must be identified and addressed. Example misconceptions include an inability to differentiate between heat and temperature, the notion that transfer of heat will always result in a temperature rise, and a misunderstanding of the concept of latent heat. The purpose of this activity is to review basic concepts of thermal physics and highlight applications to ocean processes by focusing on the concept of thermal expansion.

Most substances expand when heated and contract when cooled. As the temperature of most substances increases, their molecules vibrate faster and move farther apart, occupying a larger space. When these substances are cooled, their molecules vibrate slower and remain closer to each other. Note that freshwater below 4°C actually expands when cooled, a phenomena known as the anomaly of water. Thermal expansion is the principle by which a liquid thermometer works. In the ocean, thermal expansion is thought to contribute significantly to sea level rise on decadal-to-century-long time scales. However, thermal effects appear to be influenced by decadal climaterelated fluctuations, making it difficult to estimate the long-term contribution of thermal expansion to sea level rise. Current estimates suggest that thermal expansion is responsible for 25 percent to 50 percent of observed sea level rise.

In this activity, we look at thermal expansion and attempt to predict what will happen to the ocean's volume if ocean waters become warmer. Credit: Karp-Boss, L., E. Boss, H. Weller, J. Loftin, and J. Albright (2009). Teaching Physical Concepts in Oceanography: An Inquiry Based Approach. Oceanography 22(3), supplement, 48 pp.