#9: Clouds, Air Pressure, and Temperature
(Cloud in a Bottle) (pdf)
Most clouds are produced by the cooling of moist air moving upwards in the atmosphere. The cooling is produced by the expansion that occurs when rising air is subjected to the lower air pressures at higher altitudes. Sinking air, on the other hand, is compressed by greater air pressure and warms. Any misting cloud in the descending air tends to evaporate away because of the warming.
Upon completeing this investigation, you should be able to:
Describe how air temperatures change as air pressure changes.
Make clouds appear and disappear.
Explain how most clouds form and dissipate in the atmosphere.
Acquire a clean. clear plastic 2-liter or larger beverage bottle with cap, thin liquid crystal temperature strip (available wherever aquarium supPlies are sold), tape, paper strip slightly shorter than temperature strip.
Tape the paper strip to the ends of the temperature strip to bend it into an arc with the face of the thermometer on the convex side. Gently slide the temperature strip into the dean, dry bottle. Screw on the cap tightly.
lay the sealed dry bottle on its side on a table so the temperature strip inside faces upward and is 'easy to read.
Air Pressure and Temperature Relationships
Observe and record the increase or decrease of the temperature of the air inside the bottle as indicated by the temperature strip. Place the bottle so about half of it extends beyond the edge of your desk or table. Standing and with one hand on each end, push down hard on both ends of the bottle so it bends in the middle and compresses the trapped air. Hold it this way to keep the air compressed while carefully reading the temperature strip. After a half minute or so, release the pressure by letting up on the bottle. Continue to carefully observe te temperature strip response to the pressure release.
1. What happened to the air temperature in the bottle as a result of the air being compressed?
2. When you released the bottle so the air inside was no longer being squeezed, what happened to the air temperature?
3. What relationships do you see between changes in air pressure and temperature?
Making Clouds Appear and Disappear
Open the bottle and pour a few drops of water in it. Twist and turn the bottle to wet the inner surface. Cap tightly and let stand for a couple of minutes so enough water evaporates to saturate the inside air.
Lay the bottle on its side, open the bottle and push down to flatten the bottle to about half its normal diameter. Have someone light a match, blow it out, and insert the smoking end into the bottle opening. Quickly release your pressure on the bottle so it returns to its rounded shape and the smoke from the extinguished match is drawn inside. Quickly cap the bottle tightly. The smoke was added to the air because atmospheric water vapor needs particles present on which to condense.
Now apply and release pressure on the bottle as before, keeping track of temperature changes. Look very carefully in the bottle for any evidence of a cloud. It would be detected by a change in air visibility. If you cannot detect a cloud, repeat the process under different lighting conditions. Try leaning the bottle lenghtwise across a counter edge, and pressing with your body weight on both ends to maximize your leverage in creating compression.
4. Did the cloud form when you applied pressure or when you released pressure?
5. Did the cloud form when the internal temperature rose or fell?
6. What is the technical term for boiling liquid water into water gas (vapor)?
7.What is thew technical term for the reverse process in #6 above?
8. Gas (vapor) phase water is invisible to human eyesight. What phase is the water in the bottle in when no cloud is present?
7. Liquid phase water (micro droplets) are visible to human eyesight in aggregate (large samples) as clouds. What must happen to the temperature or pressure to form clouds?
CLAIM: Clouds form in Earth's atmosphere when water vapor (invisable gas phase) and suspended particles (colloids) are present in response to changes in temperature &/or pressure.
1) An increase in temperature or pressure results in_____________________________(fill in the blank)
2) A decrease in temperature or pressure results in ______________________________(fill in the blank)