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Clouds are condensations of moisture in the atmosphere.
Any of the following experiments help you realize that real
clouds are formed similarly through the cooling and
condensation brought about by the expansion of rising air.

Do these projects under adult supervision.

a. Pour a cup of warm water into a transparent wide-mouthed
gallon jar. Hold a lighted match in the jar, and blow
the match out, letting it remain in the jar briefly.
Now put a plastic bag in the jar, turn the edge of the
bag over the jar rim, and fasten the bag securely with
rubber bands. Hold the jar firmly on the table with one
hand, and with the other hand quickly pull upwards on the
plastic bag.

You will see a cloud form inside the bag; when the bag is
released, the cloud will disappear. The cloud forms for
several reasons:

(1) The air in the jar contains invisible water vapor;

(2) the air pressure inside the jar was reduced by the
lighted match;

(3) there are many small particles from the match in
the air.

As the air inside the jar expands, it cools, and the water
vapor condenses as liquid around the smoke particles to form
the minute droplets that make up the cloud.

Test to see if a cloud can be made:

(1) without putting water in the jar,

(2) with cold water instead of warm, and

(3) with water but without smoke, and so on.

b. Obtain two identical wide-mouthed jars. Line half of the
inside of each jar with a soft black cloth. Add glue to
hold the cloths in place, then soak the cloths with
water. Cover each jar with a square of glass or plastic,
and set them upright, one in a pan of cold water, the
other in a pan of very hot water. Leave the jars in the
water for 15 minutes, then remove them from the pans.

Set the cold jar upside down over the warm jar, leaving
the glass squares over the openings. Hold a flashlight
so that it shines down through both jars, then carefully
remove the glass squares.

A cloud will form as the warm moist air rises and comes in
contact with the cooler air above.

Experiment by repeating the activity and reversing the
positions of the jars. Tiny tissue paper streamers can
be placed inside the jars to indicate the direction of air

If possible, observe cloud formations outdoors. Make a
judgment about the relationship of hot and cold air masses,
based upon your experimental model.

Why are clouds flat on the bottoms?

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