The Energy Demonstration

Understanding the role that energy plays in phase changes is a crucial concept in weather. How often have you heard a television weatherperson say that "this storm has lots of energy"? This "energy" is absorbed by water molecules as they evaporate from the ocean. . . the more vapor, the more energy. Then as the vapor molecules condense or freeze to form clouds, this energy (latent heat) is released. This heat can make the air lighter, causing it to rise, causing the pressure to decrease, and causing winds to increase.

Another weather phenomenon caused by this latent heat is the "Chinook effect". When humid air forms lots of clouds on the west slopes of the Rockies, lots of heat is released. As this air descends onto the east slope of the Rockies it is warmed by both compression and the heat that was given off by this cloud formation.

In the "Energy Demo", one thermometer is kept dry, one is soaked in room temperature water, and one in alcohol. Let them set for several minutes. As molecules evaporate from the two wet bulbs, energy (heat) is removed from them. Since alcohol evaporates faster than water, that thermometer gets cooler than the other two. (This is how "sweating" is supposed to cause a cooling effect.)