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Heat Flow and Latent Heat

Grade level: 5-8
Theme: water cycle
Activity: http://www.tos.org/hands-on/teaching_phys_concepts.pdf

Activity 4.5: Heat Flow and Latent Heat (p. 37-38). 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 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 latent heat.

When an object gains heat, two things can happen: the temperature of the object can rise, or the object can change its state without a measurable change in temperature (e.g., ice melting into water). Most materials have two state transitions: from solid to liquid and from liquid to gas. The heat needed to change the state of a material is called latent heat of fusion (for changing from solid to liquid) and latent heat of vaporization (for changing from liquid to gas). Latent heats of fusion and vaporization for water are high and have many important consequences for Earth's climate.

Flash Video | QuickTime Movie
 
Student Outcomes 
After completing this activity, students should be able to:

Explain the energy conversions found in the water cycle (e.g., evaporation requires heat energy, condensation releases heat energy). (W: 5-8)

Key:  C = climate / O = ocean circulation / T = 21st century technology / W = water cycle