Example of Learning Cycle Lesson : Canned Cloud (cloud formation)
Exploration
Give to each of the student research groups a canning jar, ice, matches, and black construction paper. Ask the students to create a cloud in the jar under each of the following conditions:
Fill the jar with about 2cm of hot water. Invert the lid and place on top of the empty jar. Does a cloud form? (I have students write observation in environmental journal)
Fill the jar with about 2cm of hot water. Invert the lid and place on top of the empty jar. Add ice cubes to the inverted lid. Does a cloud form? (I have students write observation in environmental journal)
Fill the jar with about 2cm of hot water. Invert the lid and place on top of the empty jar. Add ice cubes to the inverted lid. Light a match, drop into jar, and cover quickly with the ice filled lid. Does a cloud form? (I have students write observation in environmental journal)
Concept Development
I discuss the observations with the students and pose questions to lead them to identify the three essential components of a cloud as being water vapor (hot water), a lowered temperature or change in temperature (made possible by the ice), and a condensation nucleus or small particle upon which the condensation can occur (the smoke from the match). Identify the temperature at which a cloud forms as the dewpoint. Review the relationship between dewpoint, air temperature, and relative humidity. Help students understand that clouds may form when the relative humidity is 100%.
Concept Application
Give the students a two-liter bottle. Ask them to add 2cm of hot water to the bottle, spray with a small amount of air freshener, and quickly put on the cap. If they squeeze and release the bottle, they should see a cloud form. Ask them to write down their explanation of how the cloud was formed in light of their previous experience.
Students should note that two of the ingredients necessary for cloud development, water vapor, and condensation nuclei were obviously present. They probably will have a difficult time accounting for the temperature drop they observed in the previous experience. Explain that when they squeezed the bottle they were compressing and separating air molecules. When air molecules separate, they collide less often generating less heat. This cooling effect has the same effect on cloud formation, as did the ice cubes in the previous experience.
I show students a diagram of the pressure and temperature changes that occur in the troposphere with altitude. I ask students to explain the formation of clouds from rising air using both text and a diagram in their environmental journal.
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