This Week's Experiment - #224 Easy Cloud in a Bottle
For this week's experiment we are going to make a cloud. It won't give us
any rain, or produce lightning, but it will give us an idea of how clouds
form. You will need:
a clear, two liter soda bottle with its cap
water
paper
a match or lighter
WARNING! This experiment uses fire. Be sure you get permission. Be very
careful and use common sense.
Before we make our cloud, we need to be sure we can see it. Take a clear,
two liter soda bottle and remove the label. Be sure you saved the top and be
sure that it fits tightly.
Now for the experiment. What are clouds made of? Water, right? So the
first thing we need to do is put a little water into the soda bottle. It
does not take much. Just enough to cover the bottom of the bottle. Next, we
need to get the water to change into water vapor. An easy way to do that is
to put the cap on the bottle and shake it a bit. This covers the inside of
the bottle with water. The more surface that is wet, the faster some of the
water will evaporate, adding water vapor to the air.
Once you have lots of water vapor in the bottle, look carefully to see if you
can see a cloud forming. Do you see one? No? Why not? The water vapor is
invisible. To see a cloud, we need to change the water vapor back into
liquid water. How can we get the water vapor to condense back into a liquid?
One way to do that is with a sudden drop in air pressure. Squeeze the
bottle very hard and then quickly release it. Did you get a cloud? Probably
not. Why?
Squeezing the bottle raises the pressure and the temperature. This allows
more water vapor to evaporate. Quickly releasing the bottle lowers the
pressure and cools the air. That cooling causes some of the water vapor to
condense back into liquid water. Then why don't we see a cloud in the
bottle? The water vapor needs something to condense onto. That could be
tiny piece of something like dust, but in our experiment we will use some
particles of smoke. Do this over the sink, so we don't start a fire. Cut a
long, thin strip of paper. It should be thin enough so that it easily fits
into the mouth of the soda bottle. Remove the cap from the bottle.
Carefully use the lighter to set the end of the paper strip on fire. Give it
a second to burn and then blow out the flame. When it is out, you will see
smoke rising from the burned paper. Quickly stick the end of the paper into
the bottle, so that a little smoke gets inside. Remove the paper and put the
cap on the bottle tightly. You will not see any smoke in the bottle, but
some of the particles are still in there.
Once again, squeeze the bottle very hard and quickly release it. Watch
carefully and you should see a thin fog appear in the bottle. Squeeze it
again and release. The cloud gets thicker. After you do this several times,
you will have a very nice cloud in your bottle.
Notice that when you squeeze the bottle, the cloud vanishes. Squeezing
raises the temperature and the water droplets quickly change back into water
vapor. The increase in temperature also helps more water vapor form from the
water on the sides of the bottle, so as you do the experiment several times,
you get more and more cloud. If you look carefully, you might even be able
to see the silver lining. Have a good week.
From Robert Krampf's Science Education Company
PO Box 60982
Jacksonville, FL 32236-0982
904-388-6381
krampf@aol.com
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