Module 6: Atmospheres & Fluids


Overview: Use a clear 2-liter plastic bottle to make an artificial cloud. This gives some help in understanding condensation and evaporation. Discuss the results and consequences in the *main* Module conference.

1. Obtain a clear plastic bottle, preferably 2-liter. Remove the label and rinse it thoroughly. Leave a little bit (a few tablespoons or so) of water, put the cap on firmly, and let it come to room temperature.

2. Squeeze the bottle and release it a few times. Do you notice anything happening?

3. Loosen the cap so you can remove and replace it quickly. (Don't leave it off for too long, or you might loose some of the humidity inside.)

4. Light a match and let it burn for a moment. Remove the cap from the bottle, blow out the match, and immediately drop it in the bottle and replace the cap tightly. The idea is to get some smoke inside the bottle without significantly altering anything else about the air in the bottle.

5. Squeeze the bottle and release it a few times. Do you notice anything happening? (If not, try looking through the bottle longways. Note which change occurs with squeezing and which with releasing.)

VARIATION: Relation of pressure and temperature.

For this, you need a clean, dry 2-liter bottle (label removed) and an aquarium thermometer ($1-$2 at a pet store - the liquid crystal kind - get the one with the smallest divisions, or Farenheit, if you have a choice). You may wish to get two identical ones, to use one in the above cloud experiment.

a. Replace the peel-off backing by a piece of cellophane tape that's longer than the thermometer. Bring the ends of the tape together so the thermometer makes the curved side of a "D" as seen from the edge, and the tape ends make the straight side. Use a short, narrow piece of cardboard (I cut it from the package) to put a crosspiece in the middle of the tape, so that the shape is "+" . Add more tape to cover up any remaining sticky parts - don't cover the front of the liquid crystal part, though. The point is to make a shape that will land thermometer-side up easily, and where the thermometer will be exposed to air rather than to the side of the bottle.

Temporarily roll the flexible thermometer, insert in mouth of bottle, and attach the bottle cap firmly. You should be able to read the thermometer through the bottle.

b. Allow bottle and thermometer to reach equilibrium (come to room temperature). Read the temperature. Note carefully the colors at each temperature (slight changes of temperature will affect the color before clearly changing the next unit higher or lower).

c. Wearing gloves or using some other kind of insulation (so you don't add the heat of your hands to the bottle), place the bottle so about half sticks out over the side of a sturdy table. Bend the bottle over the edge of the table (this is easier than just trying to squeeze it, and easier to hold). Watch the thermometer for a minute or two, and note any changes.

d. Allow the bottle to return to normal, and again note changes over a minute or two.

e. If it does not return to the original temperature, repeat b-d. (Your hands may have added some warmth...)

f. If there was a sufficient change, it may be worth trying again with some moisture in the bottle. In this case, don't dump water in, but use a moist cotton ball or tissue. Allow some time for evaporation & equilibrium. Does the temperature change the same way? The same amount?

Turn In: Summary individually to homework conference - be sure to address the points mentioned above, as well as a general summary of what you did and what you discovered.

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last updated 4/7/02