Grades
5-12
Group size
Whole class
Time required
15 minutes
Materials
Instructional Goal
Objectives
Student will:
Prerequisite Knowledge
Clouds form when air rises and expands. As the air rises, it cools.
Cold air does not hold water vapor as warm air. If condensation
nuclei are present, water vapor condenses as it cools to form tiny
water droplets. Fog is a cloud close to the ground.
In this activity, condensation nuclei are provided by a wisp of smoke. In the atmosphere, water droplets condense around dust particles.
This demonstration shows that rapid decrease in pressure will lower the temperature of a gas (Gay-Lussac's Law).
Advance Preparation Time
Get materials
Teacher tips
Clouds, rain, wind and other weather phenomena are not only desirable but may be necessary in orbital space settlements. Beautiful clouds may also be visually appealing and give a sense of outdoors to the colonists. From studies in biosphere 2 we now know that wind is essential for trees. Wind causes the branches of trees to be strong, and grow in an orderly fashion. This activity will give students some ideas on how clouds could be formed in space settlements. Very moist air would be pressurized and be allowed to expand into slightly dusty or smoky air. When moist air expands, clouds will form with dust and smoke particles becoming "seeds."
Step 1
Blow up the balloon once to stretch it. Deflate it and cut
off stem. Stretch the balloon over the mouth of the jar to make sure
it fits tightly. Then remove it, but keep it ready to replace
quickly.
Step 2
Put about a teaspoon of water in the bottom of the jar.
Step 3
Drop a burning match into the jar to provide a wisp of smoke.
Immediately cover the mouth of the jar with the balloon. Fasten the
balloon in place with the rubber band. The air in the jar has been
"seeded.".
Step 4
Push down on the center of the balloon with your knuckles.
This compresses the air in the jar and increases the pressure.
Step 5
Grasp the balloon in the middle between your thumb and
forefinger, and pull up on it quickly. The sudden decrease in
pressure cools the air. With a little luck a "cloud" will form in the
jar. If you push down and pull up again quickly, the cloud will
disappear and reappear again and again.
A beam of light directed through the jar and a dark background will make the effect more dramatic.
Enrichment Activities
If you have access to lab equipment, a better way of doing this
demonstration is by using a bicycle hand pump or compressed air.
Instead of a jar, use a bottle with a one hole rubber stopper. After
throwing the match into bottle, immediately raise the pressure inside
the bottle by pumping air into the bottle through the hole of the
rubber stopper. Let the air expand, by lifting the bicycle pump out
of the rubber stopper hole. Immediately shine the flashlight to the
bottle to show the "cloud" that formed inside the bottle. Repeat to
show the students that this is a reversible process.
Illustration is by Leyla Sezen.
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Author: Tugrul Sezen BACK
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