Physical Science: Session 2
Evaporation and Condensation; FOSS
at a Glance:
Curriculum: Full Option Science System (FOSS), Water Module: Investigation 3, Water Vapor, Delta Education
Grades: Third and fourth
Topic: Evaporation and condensation
Prior to teaching Water Vapor, Linsey led her students through a hot and cold water investigation, in which they compared the properties of water in liquid and solid (ice) states.
Linsey introduced Investigation Three by asking the students to recall a recent recess period during which they observed that the ground outside had become dry after a brief rain shower earlier in the day. In the discussion that followed, their interpretations of what happened were clearly informed by what they learned about the water cycle in second grade.
This led to an experiment in which they took two paper towels and soaked them in water, rung them out, and then put them in plastic cups on a balance and made sure they were equal. They then covered one cup and left the other exposed to the air overnight to see what would happen the next day. “Some of the kids predicted that it depended on where the balance was placed in the room,” Linsey said, “and some thought that it depended on whether we left the lights on all night. The ones who predicted that the covered cup would drop realized that the paper towel in the uncovered cup was exposed to air.”
In a follow-up lesson, Linsey’s students watched as water droplets condensed on the outside of a plastic cup filled with cold water and then tried to explain why the same phenomenon didn’t occur on a cup filled with room-temperature water.
“ I would say that the big idea of both of these lessons is getting the students to understand that water is in the air. Where does the water go? Well, it’s everywhere. You know, getting them to understand that water vapor is part of the cycle, that it is a gas, and that it can change back into a liquid again. I’ve been teaching this unit for four years, and every time I find that I really need to ask the students what they know about things ahead of time, in order to help me to know where to go as well.”
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