Lesson: Evaporation

Prerequisites:

Objectives:

1. To demonstrate the concept of evaporation

Materials:

• Plates - styrofoam or plastic, not paper (enough for partners)
• one purple, orange, black crayon for each group
• Water
• Sponge
• Measuring cup
• Humidity Detector - optional

Introduction:

Body:

• Demonstration:
  1. Do this lesson on a dry day, not a rainy or a foggy day. Divide the class into partners. Each pair needs a plate and three different colored crayons. Each pair should make a shallow puddle of water on their plate. Then they should use a purple crayon to make a circle around their puddle of water. Have each pair choose different places in the room to place their plate (i.e. in the sun, in the shade, near a heat register, etc.). Let the plates sit for about an hour. During that time make some predictions about what will happen to the puddles of water. Ask:"If we leave our puddles of water in the spots we chose around the room, what do you think the puddles will look like in one hour? What will happen to the water? Will the puddle be the same size? Will it be larger or smaller?"

  2. After about one hour has passed, have each pair check their puddles. Each pair should make a orange circle around their puddles if the puddles have changed any. (The puddles should shrink.) The different groups can compare puddles. Have each pair leave their plates and puddles where they are for one more hour. During this time compare the predictions the children made about what they thought would have happened to what actually happened. Also discuss what the students think will happen to their puddles in the next hour. Ask:"What will your puddles look like in one hour? What will have happened to the water? Where does the water go? Do you think there will even be a puddle left? Why?"

  3. After one hour, recheck the puddles. Each group should make a black circle around the new puddle. The groups can compare the puddles again. Have a discussion about what happened to the water. Some possible questions to ask are: If there are differences in how fast puddles in different parts of the room evaporated, discuss reasons for that:"Who's puddle shrunk, or evaporated faster? Why? (Relate this to the locations in the room). What happened to your puddles? Where did the water go? What types of places helps evaporation to happen faster?" The teacher will want to direct the students, if necessary, to the idea that water goes into the air and that we call this process evaporation. Have the students leave their plates where they are overnight, so that they can check them again in the morning. Ask : "What do you think the puddle will look like when you come back to school next time?"

• Analogy:
  1. In front of the class, take a dry sponge and squeeze it to show that there is no water in the sponge. Ask: "How much water is in the sponge?" Holding the sponge in the air and using a tablespoon, slowly pour water onto the top of the sponge one tablespoon at a time. Have the students count aloud the number of spoonfuls you adding. While doing this ask: "What is happening to the water? Where is it going? What do you think is going to happen as I keep filling the sponge with water? Can I put water into this sponge forever? Will we be counting forever?" Keep adding water by the tablespoon until the sponge is saturated and starts to drip water. Ask: "What has happened to the sponge? Why is water dripping from the sponge? Pretend the sponge is air, what does the water dripping from the sponge act like? (rain or a cloud) Does anyone know another name which means something is full of water like the air or the sponge?" (If no student knows saturated, then explain: "When air is full of water like the sponge is full, we say the air or the sponge is saturated.) Record on the board : sponge full = ? spoonfuls of water.

  2. Ask the students : "Can you tell me how many tablespoons of water I poured into the sponge when it was only halfway full of water?" Record on the board : sponge 1/2 full = ?/2 spoonfuls of water. Ask the students : "How many spoonfuls of water were in the sponge when the sponge was empty?" Record on the board : sponge empty = 0 spoonfuls of water. Ask the students : "How many tablespoons of water would be in the sponge if the sponge were nearly ready to rain or drip? How many tablespoons of water would be in the sponge if it were nearly empty but not totally empty?" Explain: We can now use our scale to measure how close our sponge is to raining. Weatherpeople can measure how close the air is to raining by using a humidity scale. Next to the scale for the sponge, make a corresponding scale for air labeled humidity. Write on the board dry air = 0; wet air = 100. Ask: "If the air almost ready to rain, what would the humidity scale say? If the air were nearly but not completely dry, what would the humidity scale say? If the air were halfway full of water or halfway saturated, what would the humidity be?"

• Data Analysis:
  Introduce that weatherpeople can measure the amount of water in the air or the humidity using instruments called humidity detectors. If available, pass around a humidity detector for the students to examine otherwise bring in a picture to show the class. Ask the students : "Have any of you ever watched the news in the evening and heard the weatherperson give a value for the humidity?" Explain that the weatherperson may use an instrument like the humidity detector to determine the amount of water in the air or the humidity. Have the students record humidity values in their weather journals. The humidity values should be taken at the same time every day - afternoon works best. If available, measure the humidity using the humidity detectors, otherwise the values can be obtained from a radio or tv news program. <\OL>

Conclusion:

Vocabulary Words:

• evaporation
• saturation
• humidity

Evaluation:

Followup Lessons:

• Condensation

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