Introduction:

This lesson is a versatile one involving water. It would fit perfectly into a unit on the water cycle or in a unit on phase changes in general. Furthermore, once the students have witnessed evaporation with their very own eyes, they can apply the knowledge to other areas of life (see "Extensions" section). The experiment requires the students to have a preliminary familiarity with "evaporation" (at least the definition). It also requires the students to be comfortable measuring distances with a meter stick and creating a graph.

To motivate the students for this lab, ask them to explain how they can tell if something has evaporated. For example, how would they tell if a puddle evaporated. Chances are, if they understand the concept of evaporation in the context of the water cycle or phase changes, they can reason out a procedure similar to that below. The teacher may use some guiding questions if necessary. It's important, though, for the students to feel as if they have had some control over the experiment by coming up with a procedure on their own. This "authority" also helps them understand the concepts better rather than simply following directions mindlessly.

Evaporation

Variables

diameter

Divide class into small groups. Each student be responsible for one of the following jobs – tracing the puddle, keeping track of time, measuring the circles, and recording the observations.

1. Obtain approximately 1/2 liter of water in a container. Take this and the other materials outside near a flat, level section of sidewalk or playground.
2. Note the weather conditions (i.e. -- sunny, cloudy. hot, cold?) and record on data sheet.
3. Pour the water onto the sidewalk trying to form a circle as best as possible. Start the watch.
4. Draw around the outer edge of this "puddle" with the chalk.
5. Until five minutes is up, observe what is happening to the water. Record each group member s descriptions of what is happening to the puddle.
6. After five minutes passes, trace the size of the "new" puddle.
7. Repeat step 6 two or three more times depending on time restraints. Therefore, there should be observations for at least 15-20 minutes.
8. When ALL of the circles have been drawn, measure the diameter of each circle and record This data.
9. Make a graph of the results (diameter vs. time).

To check that the students understand the principle of evaporation and what effect the weather conditions have on the diameter of the puddle, ask the students to state what the graph would look like given different weather conditions. Make sure they justify their answers.

They could check their hypotheses for the assignment in the "Assessments" section by repeating the experiment on a day with different weather conditions. If repeating the experiment over and over is too time consuming, the teacher could perform the experiment and give the data to the class to then graph and discuss.

The effects of weather on evaporation have many applications to daily life. For example, it is best to water a garden or the lawn in the morning rather than the middle of a hot summer day so that the plants have time to absorb the water before it evaporates away. Furthermore, cities that get their water supply from uncovered reservoirs or rivers could run into water shortage problems in the summer if this water evaporates and is not replaced by condensing water in the form of rain. As other lessons would emphasize, water is a crucial component to all forms of life. Therefore. it is important to conserve water as much as possible especially during the summer months where the risk of water shortages is that much greater. Discussing these applications could serve as a motivation for the students to write letters to city officials so that the entire community was reminded of the importance of conserving water always but especially during the summer months.

Another extension of this lesson is to have the students do some kind of final project on the entire water unit. It could be in any form they choose -- e.g., collage, drawing, story, poem, or even acting out the role of water! Some suggestions are: "the uses of water", "what would life be like without water?" etc. Let their creativity run free!

SCIENCE CONTENT STANDARD # 1: NATURE OF SCIENCE

This experiment satisfies Benchmark 1 for grades 5-8: "design, modify, and conduct an investigation through testing, revising, and occasionally discarding ideas. all of which lead to a better understanding of how things work." It also satisfies Benchmark 3 for grades 5-8: "collect and summarize data from an experiment and interpret the results in terms of the data."

SCIENCE CONTENT STANDARD #2: PHYSICAL SETTING

This experiment satisfies Benchmark ~ which states that students should ' understand the effect of the . . . water cycle on natural resource management". The section in the "Extensions" involving when to water a garden especially ties in with this benchmark. Furthermore, Benchmark 7 states that students should "understand that the cycling of water in and out of the atmosphere plays an important role in determining climatic patterns. Water evaporates from the surface of the earth, rises and cools, condenses into rain or snow, and falls again to the surface. The water falling on land collects in rivers and lakes, soil, and porous layers of rock, and much of it flows back into the ocean."

SCIENCE CONTENT STANDARD #5: DESIGNED WORLD

The introduction to the Philadelphia Science Content Standards states that students should understand "the impact of science and technology on society with a focus on populations, resources, and the environment". This experiment helps the students to see how the scientific concept of evaporation has an effect on the world's water resource.

This experiment would fit well into an earth science unit on the water cycle, or a chemistry unit on phase changes. It also reviews important math skills such as measuring and graphing. Finally, if the students are encouraged to write letters to city officials (see "Extensions" section), the lesson would also incorporate language arts skills.