Evaporation/Humidity

Grade Level: Third grade
Subject Area: Science
Approximate Time: 50 minutes

Objectives

Materials

Procedures

  1. Take a wet cloth and wipe the chalkboard so that the wet streak is visible to entire class. Ask the class to observe the wet mark. (Begin discussion in step #2) After a few minutes of observation, ask the class to share what they observed. Ask if they have any ideas as to what happened to the water. Discuss possibilities and write on board.
  2. Ask the class if anyone has ever thought about what happens to puddles when the sun comes out. Do the puddles remain there forever? Ask what happens to the water on wet clothes as they are hung to dry in the sun. Discuss possibilities.
  3. Explain to class that what these three examples represent is evaporation. Write "Evaporation" on board and describe as when water turns into an invisible form, called water vapor. Explain that vapor is water in gas form and that this vapor is around us constantly. The temperature of the air determines how much water vapor can be in the air. Ask class if they think warm or cold air would hold more water. Ask for their reasoning. Explain that warm air holds more vapor, or moisture.
  4. Explain that this moisture in the air is called the "humidity". Write the term on the board. If there is a lot of moisture in the air, then the humidity is high. Ask children how they feel when it is very humid out. Explain that there is a point when the air can hold no more water--when the humidity is close to 100%. Ask for ideas of what may happen as weather when this occurs.
  5. Have student "helpers" pour the same amount of water (exactly) on 4 Styrofoam or plastic plates. Distribute each plate in different places in the room (one by the heater, one in the sun, one in the shade, one in a cold, dark area). Draw a circle, with a wax pencil, around the puddle. Tell class that we will check how much water is on the plate tomorrow. Ask class to predict in their journals how the puddle will look. (Will there be more or less or the same? If more...how? If less...why?) after a 24 hour period.
  6. Check the puddles the next day. Draw a circle around each puddle. Compare the amount of water in each. Have students write their findings in their journals with reasons as to why they think the way they do. Discuss as a class what happened to the puddles. Where did the water go? What types of conditions help evaporation to happen faster? Did the temperature or sun have anything to do with how quickly water evaporated? Leave plates out for another 24 hour period and compare again. Record in journals.

Evaluation

  1. Do students generate plausible ideas as to where water from the chalkboard, puddles and wet clothes go to?
  2. Check each student's journal to see if they predicted what would happen to the water on the different plates around the classroom. Did they include a rationale with their predictions?
  3. After comparing the data (the plates of water) after 24 hours has elapsed, do the students understand why some water evaporated quicker or more slowly? Did anyone attribute evaporation to the heat, or temperature of the placement in either their journals or the class discussion?
  4. Did the students record their observations and ideas about evaporation in their journals? For the first 24 hour period? For the second?

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