Purpose
To challenge the thinking of students who believe that a liquid absorbs into a surface rather than evaporating.
Description
If you have a chalkboard, wet your hand and then make a handprint on the board. As soon as you remove your hand, outline the handprint with a piece of chalk. Ask students to observe what happens to the wet handprint over time (Prain et al., 2009).
Questions to Ask Students
- Why is the handprint getting smaller?
- Where did the water go?
Student Thinking
Some students may still think that the water is absorbing rather than evaporating (Osborne & Cosgrove, 1983; Prain et al., 2009; Russell et al., 1989; Tytler, 2000; Tytler & Prain, 2007). If they do, try the activity with a surface that all students agree does not absorb water (see Student Experience 3).
Implementation Tips
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- The purpose of this activity is to give students evidence that the water is not absorbing into the surface. Don’t worry about explaining evaporation at this point.
- Instead of doing this activity as a demonstration, you can have each student make and outline their own handprint on the chalkboard.
- If you don’t have a chalkboard, you or your students can do the same activity with any dark-color construction paper. They can outline with a pencil, crayon, or marker instead of chalk. Depending on the humidity, it should disappear in just a few minutes, especially if student shake the excess water off their hands before making their handprint.