#9: Clouds, Air Pressure, and Temperature
(Cloud in a Bottle)
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.
(alternative: insert the data that increasing pressure increases temperature inside the closed bottle)
Air Pressure and Temperature Relationships
Read and record 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 die, temperature for at least a ' minute.
1. What happened to the temperature 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. State; in your own words, the relationship 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? Did it form when temperatures rose or when they fell? Why?
5. Once you have a cloud in the bottle, make the cloud disappear. What makes it disappear?
6. Most clouds in the atmosphere appear and disappear the way your bottle cloud did. State in your own words the temperature and pressure relationships that lead to cloud formation and, assuming no precipitation, cloud dissipation.
attach: your description of this activity & your observations, & answer questions 1-6 above as stand-alone explainations.