RODNEY’S HOMEPAGE for Earth Science Teachers:

LAB: What’s the Recipe for a Cloud? . . . . . . . .name:
Pre-lab Questions:

1. Which will probably have more humidity (water vapor) in the air above it ? Circle one.

. . . . . . . A) a part of the ocean having colder surface waters

. . . . . . . B) a part of the ocean having warmer surface waters

2. In order for a cloud to form, the humid air must be cooled below its ??? point. Circle one.

thermal . . . . . . . . . condensation . . . . . . . . . dew

3. As air is compressed (squeezed), will it become warmer, or will it become cooler?

4. As air is allowed to expand, what happens to its temperature?

5. What are condensation nuclei? Give two examples.

Materials: 2 liter (untinted) plastic pop bottle with lid, book of matches, 250 ml beaker (or larger), hot water, ice water


1. Trial #1: Pour 200 ml of cold water into the plastic bottle, and then firmly screw on the lid. Shake the bottle for 30 seconds. Squeeze the bottle for several seconds to increase the pressure, and then release it to allow the air inside to expand. Squeeze and release several times as you watch the air in the bottle. What happens?


2. Trial #2: Unscrew the cap from the bottle. Light a match, blow it out, and then hold the smoking match inside the tilted bottle for about 3 seconds. Quickly replace the cap. Squeeze and release as you did in procedure #1.


3. Trial #3: Empty the cold water from the bottle, and pour 200 ml of hot water into it. Replace the cap, and shake the bottle for 30 seconds. Squeeze, release, and observe.


4. Trial #4: Unscrew the cap, and hold a match into the bottle as you did in procedure #2. Quickly replace the cap, and then squeeze, release, and observe.


Follow-Up Questions:

1. Which of your four trials resulted in the best cloud formation?


2. Was cloud formation more impressive when smoke particles were present in the bottle?


3. Did the cloud appear when you caused high pressure on the air in the bottle (by squeezing), or when you caused low pressure (by releasing)?


4. Which provided more vapor in the bottle . . . the hot water, or the cold water?


5. Based on your findings, write out a recipe for cloud formation ? (3 ingredients or conditions)


6. In your experiment, what served as the condensation nuclei?


7. Why did the cloud disappear when you squeezed the bottle ? You must use the term “dew point” in your answer.


8. You can see clouds because they are made up of ??? or ???. Circle two answers.

water vapor . . . . . .water droplets . . . . . . ice crystals


9. As air rises in the atmosphere, is it compressed, or does it expand?


10. What effect does this have on the air’s temperature?


11. Circle the letters of the five situations listed below that will contribute to cloud formation.

A. Moist air is forced upward as it encounters the Cascade Mountain Range.

B. Tomorrow’s forecast calls for an area of high pressure to be centered over your region.

C. The westerlies cause air to flow down the east side of the Rockies into Browning, Montana.

D. During the afternoon, air over a large air force base begins to rise because it is so much hotter than air over the surrounding forest.

E. In autumn, the Santa Ana winds blow down from the mountain slopes of interior California out to the sea.

F. Intensely heated air over the equator rises in an area called the intertropical convergence zone.

G. As part of the global circulation pattern, air 30 degrees north of the equator is sinking in an area called the horse latitudes.

H. An intense low pressure system moves across the Midwest.

I. A cold air mass from Canada pushes into a mass of warm humid air over Nebraska.


Use a plastic pop bottle, hot water, and a match to demonstrate cloud formation for one of your parents. Have them sign here, indicating that you’ve done this.

parent signature:

Questions or comments from the parent (optional):





from RODNEY'S HOMEPAGE for Earth Science Teachers at

This lab takes about 30 minutes for my ninth grade Earth Science students to complete. We do the lab after the students have learned about humidity, relative humidity and dew point. It goes well if the students work in pairs. . . Rod Benson: Helena (MT) High School

ANSWERS TO THE PRE-LAB QUESTIONS: Do these together, or give the students a few minutes to do them, and then go over them before doing the lab.
1. A) warmer ocean water would have more vapor in the air above it
2. dew point
3. warmer
4. it cools
5. particles that provide a surface for water molecules to condense on as they change from vapor to liquid

1. Demonstrate the technique used to get smoke into the bottle. Read over Trial #1 and #2 . . . Tilt the bottle as much as you can without spilling the water. Blow the match out, and hold it in the opening of the bottle for about 3 seconds. The key to making a good cloud is getting lots of smoke into the bottle.
2. Also, tell the students to hold the bottle between their face and a light source for best viewing as they begin squeezing and releasing.
3. On trials 3 and 4, if students have a problem with condensation making it difficult to see inside the bottle, they can simply roll the bottle gently, allowing the water inside to rinse the condensation away.

Trial #1: a cloud should not form here
Trail #2: a very faint cloud may form here
Trial #3: a faint cloud may form here
Trial #4: students should see a fairly good cloud here

1. trial #4
2. yes
3. low pressure (by releasing)
4. hot water
5. vapor + condensation nuclei (smoke) + cooling (pressure decrease) = cloud
6. smoke
7. the air was warmed above its dew point, so the cloud droplets evaporated.
8. water droplets, ice crystals
9. expands
10. cools it
11. A, D, F, H, I
COLLECTING THE BOTTLES: Put a box in the teachers' room, and post a sign indicating that you "need 2 or 3-liter untinted soda bottles with lids".

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