Divide the class into partners. Distribute a glass cup or jar to each group. Add cold water to everyone's cup.
Students can leave the ice water glasses out overnight or for several hours.
If the class has studied evaporation , then discuss with them what happened to the water on the outside of the glass. If necessary refer to the evaporation lesson. Now divide the class into four or five groups. Each group should get two petri dishes, two paper clips and one tin lid. Ask a member of each group to place the paper clips in one of the petri dishes, then set the tin lid on top of the paper clips.