National Science Standards
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
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."
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.
Put about a teaspoon of water in the bottom of the jar.
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.".
Push down on the center of the balloon with your knuckles. This compresses the air in the jar and increases the pressure.
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.
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.
Author: Tugrul Sezen BACK TO COURSE MAIN PAGE BACK
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