Engage/Elicit:

Why do you think it rains more on the coast than inland?

by Flickr user Mil http://flickr.com/photos/danw/237415246/ Cannot resolve external resource into attachment. http://creativecommons.org/licenses/by-nc/2.0/

Explore:

Materials:

• Two plastic bowls filled with sand
• Water
• Incandescent lamp
• Plastic wrap
  (Optional)
• Relative humidity sensor
• Plastic bag

Procedure:

1. Prepare two plastic bowls filled with sand. Add water to the sand in one bowl, and leave the other dry.
2. Label the bowl with wet sand "coast" and the bowl with dry sand "inland."
3. Stretch a piece of plastic wrap over the tops of both bowls.
4. Place the bowls under the lamp.
5. Observe the plastic wrap. What is the difference between the two bowls?

   L5: Write your response in the box below. L4: Compare the plastic wrap between the two bowls. L3: The plastic wrap above the "coast" bowl looks ... and above the "inland" bowl looks... L2: The plastic wrap above the (*"coast," "inland") bowl looks cloudy. L1: The plastic wrap above the "coast" bowl looks cloudy.

   (Optional)

6. Put the "inland" bowl in a plastic bag with the relative humidity sensor.
7. Collect data below (DATA COLLECTION)
8. Put the "coast" bowl in a plastic bag with the relative humidity sensor.
9. Predict what the relative humidity will be like in near the "coast" bowl. (PREDICTION: DATA COLLECTION)
   What was the difference between the air near the "coast" bowl and near the "inland" bowl?

   L5: Write your response in the box below. L4: Compare the relative humidities above each bowl. L3: The air near the ... bowl was more humid. L2: The air near the (*coast, inland) bowl was more humid. L1: The air near the coast bowl was more humid.

   Why do you think there is that difference? (TEXT BOX)

Explain:

The air near the bowl representing the coast was more humid. That means there was more water in the air. As the lamp warmed up the bowls, adding heat energy, some of the water in the sand evaporated. When it condensed on the saran wrap, you could see it as a cloudy film. This cloudy film represents a cloud. On the earth, there is generally more humidity near the coast of oceans and very large lakes. The water vapor in the air can form water droplets in clouds, and eventually fall to the ground as precipitation in the form of rain or snow. For this reason, clouds form more often near large bodies of water and those areas generally receive more precipitation.

Evaluate

Ed: modification of experiment: two bowls of dry sand. Moisten one, leave the other dry. Or in one make a little pond in the middle, stick in paper trees, etc.  Measure the RH two ways? A) sheet of plastic over the bowl, observe formation of droplets. Take off the plastic and shake it (rain). B) RH sensor resting on pencils across the bowl or some way to keep it above the sand surface. Posted by ehazzard at Aug 09, 2007 10:51

Ed: could end this activity (or perhaps create another or put it in the "wrap-up" section) with a picture of a landscape with water, desert, mountains, etc. and have them indicate where the humidity would be high or low, where clouds would form, etc. Posted by ehazzard at Aug 09, 2007 10:55