Clouds in a Jar
demonstrationactivity exercisesuggested grade levels: 6- 8
view Idaho achievement standards for this lesson

Overview:
When air is compressed its temperature goes up. Warm air holds more moisture than cool air. When air expands it becomes cooler. A cloud appears and droplets are formed. As air rises there is less pressure, so it cools as it goes up. This is why rain often falls as air rises to pass over a mountain.

Objectives:
1. Students will become exposed to the climatology section of the Digital Atlas of Idaho.
2. Students will do an activity that will simulate cloud formation.

Materials:
Large glass jar Cork or rubber stopper with hole for glass tube
Glass tube Chalk dust
Water Isopropyl rubbing alcohol

Procedure:
Use the Digital Atlas of Idaho. To get there: Click on Atlas Home, Climatology, then on Cloud Imaging. This site of the digital atlas would serve as an excellent review before doing this demonstration for the class. Teachers are encouraged to review this material before having class discussion. Have your students go to these pages and click on the top of the first paragraph. Have them use the control f search function to search for and define words as: condensation, evaporation, relative humidity, and dew point.

Have discussion on:
   1. Cloud formation
   2. Condensation
   3. Evaporation
   4. Relationship of relative humidity with temperature and the water holding ability of air.

Demonstration:
   Drill a hole in the center of a cork which fits snugly into the mouth of a large glass jar. Insert a glass tube into the hole in the cork. Rinse the inside of the jar with water mixed with a small amount of alcohol. Pour out the water, leaving the inside of the jar wet. Add several pinches of finely crushed blackboard chalk. Put the cork and tube into the neck of the jar. Blow through the tube to scatter the chalk and compress the air, then suck very hard and suddenly on the tube. This will allow the air to expand. You should be able to observe the air in the jar to turn foggy like the inside of a cloud.

Questions for discussion:
   1. What happened to the pressure and temperature of the air as you blew into the jar?
   2. What happened to the pressure and temperature of the air as you suddenly sucked hard on the tube?
   3. What happened to the relative humidity as the air cooled?
   4. Why did the water condense?

Handouts/Activity links:
These are links to access the handouts and printable materials.
Cloud Imaging

Related Lesson Topics:
Climatology: Climatology

Lesson plan by Dr. Helen Challand and Elizabeth Brandt with permission from Science Activities from A to Z, 2001
Idaho Achievement Standards (as of 7/2001) met by completing this activity:
785.01
791.01
798.01
800.01
804.02