Tufts OpenCourseware
Author: Fulcrum Institute Development Team


What about phase change?

You’ve just finished some strenuous exercise on a windless and hot day and notice you’re sweating quite profusely. Suddenly a little breeze stirs and you notice instant relief. You’re cooling off! Consider what might be happening. What makes you feel cooler when you sweat?

At various points in the past weeks, your investigations into heat transfer by conduction, convection, and radiation have included a dramatic phenomenon, phase change, but it has not been the focus of attention until now. What is phase change? What happens to the energy in a system when phase change occurs and how does that affect temperature?

This Week's Plan

The question this week is – What happens to the energy in a system when phase change occurs? To address this question, you investigate how phase change – in this case evaporation – can be harnessed to cause cooling. You consider phase change at the molecular level and explore temperature change data associated with phase change of water.


  • Understand that evaporation, a phase change from liquid to gas, is a cooling process
  • Interpret a temperature change graph for water during phase change

What you need

  • Paper towels
  • Room temperature water
  • A fan (e.g., could be a small tabletop fan or a hand-made one from folded paper)
  • 2 400 ml glass beakers
  • Support stand with 3/8 in. rod and clamps
  • From your kit
    • Temperature probes
    • 2 Aluminum backed thermometers

Session Resources