Lesson 6: Fog, Dew, and Precipitation

Activities

Activity 1: Finding the Dew Point

Materials: ice, large metal can, spoon, thermometers (kit)
As you learned in Lesson 4, relative humidity is the amount of water vapor the air currently holds at a given temperature, compared to how much the air could hold at that temperature. Temperature dramatically affects the amount of water vapor air can contain.

Let's say it is 75°F outside and the relative humidity is 55%. If the amount of water vapor in the air stays the same, but the temperature goes up, what do you think will happen to the relative humidity? It will go down, because the warmer air gets, the more water vapor it's able to contain. And if the temperature goes down, the relative humidity will go up, because cool air holds less water vapor than warmer air.

When the temperature gets cold enough, the amount of water vapor the air is holding and the amount it could hold become the same, making the relative humidity 100% for that temperature. We call this the dew point temperature, because at this point, air can no longer hold any more water vapor and it starts to condense into liquid. Think about the morning after a cool night — what do you see outside on the grass? You see liquid droplets called dew, a sign that the dew point temperature was reached and water began to condense out of the air.

Dew is water vapor that has condensed on grass and plants, and clouds are water vapor that has condensed in the air. Fog is also water vapor that has condensed in the air — it is simply a cloud that has formed at the Earth's surface rather than higher up in the atmosphere.

In this activity you will measure the dew point of the air inside your house and use it to calculate the relative humidity. Conduct the experiment on the "Finding the Dew Point" sheet.
Web Link
Student Activity Page
Your child will conduct a demonstration to determine the dew point inside your house. She will then use an online calculator to figure out the relative humidity.

Questions Answer Key:

  1. If the temperature outside is 33°F, what would the relative humidity have to be to get a dew point of 23°F? (65%)
  2. If the temperature is 40°F and the relative humidity is 30%, what is the dew point? (11°F)
  3. Try to answer this question without the calculator. If the temperature is 80°F, and the relative humidity is 100%, what must the dew point be? Why? (The dew point is the temperature at which water vapor condenses out of the air because the air is fully saturated. If the relative humidity is 100% at 80°F, that means water vapor will begin to condense at that temperature. So, the dew point must also be 80°F.)

Activity 2: Amazing Precipitation

Materials: colored pencils or watercolor paints*
Precipitation has inspired great literature and artwork. In this activity, you will write a poem or descriptive paragraph about rain, ice, or snow (Option 1) or sketch or paint a precipitation scene (Option 2). Read over both options and choose one to complete.
In this activity, your child will reflect on precipitation in a creative way. In Option 1, she will write a poem or descriptive paragraph about rain, ice, or snow. In Option 2, she will sketch or paint a precipitation scene. Encourage her to read over both options and then choose one to complete.

Option 1: Writing about Precipitation

First, read the short selections on the "Precipitation Poems" page. Pay attention to the creative ways that the poets describe rain and snow. Next, write a short poem or descriptive paragraph about a rainy or snowy scene. (If you need inspiration for a scene, look at some of the links to precipitation artwork in Option 2.)

Consider jotting down descriptive words related to the five senses. How does your yard smell when it rains? How does the snow feel when it hits your cheek? What does rainfall sound like? Next, consider how you can describe the scene in a creative way. What can you compare it to? For example, "Like the tramp of hoofs" and "Like spangles dropped from the glistening crowd" are both similes that help the reader picture the sound or look of the precipitation. Once you've jotted down some ideas, write your short poem/descriptive paragraph.
Student Activity Page
Your child will read short poem selections about precipitation and then write a short poem or paragraph that describes a rainy or snowy scene. Encourage her to use as many of the five senses as possible and to try to describe the rainy or snowy scene in a creative way. Optionally, she can use the precipitation artwork linked to in Option 2 for inspiration.

Option 2: Precipitation Art

For this option, you will use colored pencils to sketch or watercolors to paint a rainy or snowy scene. For inspiration, scroll through the artwork at the following web links. Pay attention to the creative ways that some of the painters show or suggest rain (lines, streaks of gray, people with umbrellas, wet streets) or the colors and designs they use to paint snow. You may want to draw/paint the scene outside your window, imagining what it looks like while it's raining or snowing.
Web Link
Web Link
For this option, your child will look at paintings of snowy and rainy scenes and then either sketch a precipitation scene using colored pencils or paint one using watercolors. Encourage her to pay attention to the creative ways that the artists depict rain and snow. She may want to draw/paint a scene outside her window, imagining what it looks like while it's raining or snowing.

Activity 3: Make a Rain Gauge (Optional)

Materials: empty two-liter bottle*, marbles or small rocks*, masking or painters tape*, permanent marker*, ruler*, scissors*
A rain gauge is a tool that measures rainfall. If you have the time and materials, follow the instructions on the "Make a Rain Gauge" page.
Student Activity Page
If your child has the time and materials, encourage her to make her own rain gauge. Assist her as needed with cutting the two-liter bottle. When rain is in the forecast, she should place the rain gauge outside in a secure area where it won't be disturbed or knocked over. It should also be open to the sky (i.e., away from overhanging trees, porches, etc.). She should fill the bottle to the "0" line before beginning. As with other readings, your child's rain amount may differ from those provided on a weather report due to regional variations in the amount of rain.