Why Does It Rain?

Why Does it Rain?

Engagement:
   Read the book Sylvester and the Magic Pebble. By: William Steig. Summary is that a young donkey named Sylvester find a magic pebble and sic overs that it will grant his every wish as long as he is holding it. But to his dismay, a frightening encounter with a lion causes him to panic and make a wish to be a rock. He spends a year as a rock-through all the seasons and through all kinds of weather- and finally in springtime retires to his true donkey self. iN the end the magic pebble is stored in a very safe place. The connection to this book is weather. the foundations of the weather are lights, air, and water.

Exploration:
Materials:
   Glass
   Ice Cubs
   Water
   Paper towel sheets, one per person
   Humidity scale (figure 1.1; enlarge it so its easy for students to see)
   Science journals
   Weather Instruments: rain gauge

Figure 1.1 (On the tackk)

   As you fill the glass with ice cubes and water, pose this question to students: how do we know there’s water in the air? Invite speculation from the students, then observe the glass to note the moisture that has formed on the outside. When the cold glass meets the warmer surrounding air, water in the air condenses and forms droplets on the outside of the glass. Ask the students: How does it get there in the first place?

Explanation:
   Wet and carefully squeeze out excess moisture in the paper towel sheets, then take them outside and place them in various locations: a shady spot, laid flat in direct sunshine, held and waved in the sunshine. Ask the students what happens to the paper towel. (The towels dry as the water evaporates). Evaporation adds water vapor to the air. The amount of moisture (water vapor) in the air is called humidity. Show the humidity scale (figure 1.1). When the humidity reaches the top of the scale, or 100 percent, meteorologists say the air is saturated, which means that it can’t hold nay more water vapor. If the humidity measure somewhere near the bottom of the scale, meteorologists say there’s room for lots of water vapor in the air.
   Clouds form when the air is near saturation. Have students study the sky and estimate the humidity level based on the cloud cover. (The more extensive the cloud cover, the higher the humidity)

Elaboration:
   Draw figure 1.2 on the board and have students use their science journals to draw along with you. Talk about each component as you draw it.

Figure 1.2 (On the Tackk)

Evaluation:
Divide the class into five groups and have each group research and prepare posters illustrating the three basic cloud formations (cumulus, stratus, cirrus), fog, and dew. Present the poster to the class.
Set up a rain gauge in the weather station and have the students practice identifying clouds review the terms that will be used for reporting cloud cover on the data collection sheets: cloudy, partly cloudy, clear.