Anna Cajiga
SME 301
Weather Summary
February 24, 2005
Title
Make a Cloud in a Jar!
Benchmark
Area: Earth Science
Category: Atmosphere and Weather
Benchmark: Explain the behavior of water in the atmosphere (Middle School).
Misconception
Clouds are made of cotton, wool or smoke.
Background
There is a common misconception that clouds are made of cotton, wool or smoke.
However, this activity illustrates that clouds are actually made of tiny droplets of water. When
the water on the earth’s surface is heated enough by the sun that the molecules that make up the
water begin to move faster and bump into each other harder, the molecules in the liquid water
move further apart and the substance evaporates into a gas. This gas then rises higher into the
atmosphere with rising warm air, which rises because it is pushed upwards by denser cold air.
Once it reaches the cooler upper atmosphere, the speed of the molecules slows, and the gas
condenses around tiny particles of dust and other matter in our atmosphere. The gas can
condense into a liquid, or if it is cold enough it can become ice. Either way, clouds are formed in
the atmosphere through this process.
Materials
Gallon Size Ziploc Bag Filled with Ice
Large Glass Jar
Black Paper
Tape
Matches
Warm Water
Food Coloring
Flashlight
Directions
1. Tape the black paper to the backside of the glass jar, so you can see into the jar, but not all the
way through it. It should look like this when you are done:
Cajiga 2
2. Add food coloring to the warm water. Swirl the water until the food coloring is evenly mixed
throughout.
3. Pour the warm colored water into the glass jar until the glass jar is 1/3 full.
4. Begin to shine the flashlight on the glass jar. Continue shining the flashlight on the glass jar
until the conclusion of the experiment.
5. Light a match and hold it in the glass jar for a few seconds, then drop it into the water.
6. QUICKLY cover the opening of the jar with the bag of ice.
7. Record your observations.
Results
At the conclusion of this experiment, a cloud is visible in the glass jar. The cloud forms
above the surface of the colored water and below the bag of ice resting on top.
Discussion
This activity illustrates how clouds are created in the earth’s atmosphere. Cloud
formation is initially the result of the air surrounding the earth having differences in density and
pressure. The air in the earth’s atmosphere is a mixture of gasses, including nitrogen, oxygen,
water, argon and carbon dioxide. These gasses, like all matter, are made up of molecules, take up
space and have a mass. Since air has a mass, it is able to press on other objects. The air in the
earth’s atmosphere presses down on the earth’s surface. We call the amount that the molecules in
the air are pushing against the earth “air pressure”. The density of the air causes air pressure to
change. Air with a higher density will push down more on the earth than air with lower density.
When the temperature of air changes and it becomes colder, the molecules that make it up begin
to move slower and they bump into each other with less force. As a result, the molecules move
closer together so there are more air molecules per cubic space, thus making the density higher.
On the other hand, when air becomes warmer, the molecules move faster, bump each other
harder, and as a result move further apart. This causes there to be fewer molecules per cubic
space, which makes the density lower. This is why cold air has a higher density than warm air.
Air masses of different temperatures do not mix together. Rather, the air mass with the higher
density presses against the air mass with the lower density. Since cold air has a higher density
than warm air, it pushes against warm air, making warm air move upwards. The movement of air
from areas of high pressure to areas of low pressure creates horizontal movements of air, known
as wind. The heating and cooling of air also creates vertical movements, known as convection
currents. Convection currents are the cycle of air rising and sinking because of temperature
differences. The air at the earth’s surface is heated as light energy from the sun is transmitted to
earth, absorbed into the earth’s surface, transformed to heat energy and radiated back into the
atmosphere. This causes the molecules in the air to move farther apart, so the air becomes less
dense and begins to rise. The air then cools in the upper atmosphere and the molecules move
closer together. This makes the air become more dense, which causes it to sink back to the
earth’s surface. The cycle then continues. It is this cycle that causes the formation of clouds.
Water molecules evaporate into the air when the water is heated by the sun enough for the
molecules on the surface of the water to move faster, bump into each other harder, spread further
apart, and therefore evaporate into a gas. The water molecules then rise into the atmosphere with
the rising warm air. Once they reach the cooler upper atmosphere, the speed of the molecules
slows and the gas condenses into liquid, or ice if it is cold enough. We see this process occurring
in the activity. The air in the jar represents the atmosphere, and the warm water in the jar
Cajiga 3
represents the water on the earth’s surface. When this water is heated by the sun (the match),
water from the surface evaporates into the air, forming a gas. The warm water in the jar heats
some of the air that is touching the surface of the water, and when this water rises because it is
less dense than the cooler air, it takes the water vapor with it. When the warm air touches the bag
of ice on top of the jar, which represents the cooler temperatures found in our upper atmosphere,
the water molecules are cooled and they begin to move closer together. As the molecules move
closer together, the water vapor condenses onto the particles of smoke from the match
(representing the particles of dust in our atmosphere). This creates tiny droplets of liquid that can
be seen in the form of a cloud.
The original source of energy for all the movement of air on earth is the sun, which heats
the atmosphere. The atmosphere extends for about 200 miles above the earth’s surface. Four
layers make up the atmosphere, the first two being the troposphere, which extends from the
ground to about 6 miles up, and the stratosphere, which extends from 6 miles to 30 miles up. The
molecules in the atmosphere are what create the weather we experience here on earth. The sun is
the source of the heat in our atmosphere. The sun is a star that gives off large amounts of light
energy. This light travels through space until it reaches the earth’s atmosphere. Once this light
energy reaches the atmosphere, three things happen. About 30% of the light rays hit the
molecules that make up the gasses in the atmosphere and are reflected back into outer space.
About 20% of the light rays are absorbed by molecules in the atmosphere and transformed into
heat energy. This heat energy is radiated back out towards space and does not heat the earth’s
surface at all. The rest of the light rays, about 50% of them, are transmitted, meaning they either
travel straight to the earth’s surface, or they pass through molecules without being absorbed on
their way to the earth’s surface. Once these light rays reach the earth’s surface, they can again be
reflected, absorbed or transmitted. When the light energy is absorbed by the earth’s surface,
whether it is water or land, it is transformed into heat. This heat then radiates back out into the
air above the earth’s surface, otherwise known as the atmosphere. The reason that this heat can
remain in the atmosphere is because of the greenhouse effect. This occurs because when the heat
energy radiates into the air, it hits greenhouse gasses in the earth’s atmosphere and bounces back
towards the earth’s surface. This traps the heat close to the surface. A certain amount of
greenhouse gasses is a good thing because they allow the earth to maintain the proper
temperature for us to survive, but many of our daily activities are adding more greenhouse gasses
into the atmosphere. For example, burning fuels adds carbon dioxide into the air. An increase in
activities that add greenhouse gasses into the atmosphere is causing more heat to be trapped
close to the earth’s surface. This is called global warming and it results in increasing
temperatures, which can have detrimental effects on the delicate balance of our global
ecosystem.
It is not the heating of the atmosphere alone that creates movement of air. The fact that
the earth’s atmosphere is heated unevenly is the reason that air has different temperatures, and
therefore is able to move from areas of high pressure (low temperature) to areas of low pressure
(high temperature). There are several reasons why the earth’s atmosphere is heated unevenly.
Because of the tilt of the earth and the revolution of the earth around the sun, we have changing
seasons here on earth. During the summer months at a particular location on the earth’s surface,
there will always be more hours of daylight than there are in the winter months. During the
summer the sun is also higher in the sky, which causes the sunlight to be more direct, and
therefore more intense than it is in the winter. These two factors contribute to more light energy
from the sun being absorbed into the earth’s surface, transformed into heat and then radiated into
Cajiga 4
the atmosphere. Also, a similar effect occurs at locations that are closer to the equator because
the closer to the equator a location is, the higher in the sky the sun is, and the more hours of light
a location has. Similarly, this allows more light energy from the sun to be absorbed into the
earth’s surface, transformed into heat and radiated into the atmosphere. Different materials also
absorb light energy differently. For example, land absorbs light energy more than water does
because water reflects more light energy away than land does. The reason for this is because the
molecules in land, a solid, are closer together than they are in water, a liquid, which makes land
have a higher density so it absorbs more light energy than the water. The fact that land and water
absorb light energy differently causes more heat to be radiated into the air above land than into
the air above water, creating an unevenly heated atmosphere. Different colors also absorb light
energy differently. Dark surfaces will absorb more light energy than light surfaces will, which
also contributes to the earth’s surface being heated unevenly.
Understanding more about weather helps explain many other everyday occurrences. For
example, anyone who has ever been to the beach has surely noticed that sometimes the sand is
almost unbearable to step on, but the water remains cool and refreshing. Understanding the
absorption of light energy from the sun by the earth’s surface makes it clear that this happens
because the molecules in the sand are closer together than those in the water. This causes the
land to be able to absorb more light energy, and transform it into heat energy, making it very hot
to the touch. Understanding light energy absorption also explains why people are often reluctant
to wear dark clothes in the summertime. This is because dark surfaces absorb more light energy
than light surfaces do. The light energy is in turn transformed into heat energy, so dark surfaces
radiate more heat than light surfaces do, which would be very unpleasant in warm weather.
Knowledge about air at different temperatures explains how hot air balloons work. Since the
molecules in warm air are further apart from each other than the molecules in cold air are, warm
air has a lower density. This causes warm air to rise, which is why hot air balloons, full of air
that is much warmer than the air in the surrounding atmosphere, are able to rise into the air. In
recent years there have been many efforts to reduce the burning of fossil fuels to reduce the
greenhouse gasses in our atmosphere. The burning of fossil fuels releases carbon dioxide into
the atmosphere. Learning about weather teaches that carbon dioxide is a greenhouse gas.
Greenhouse gasses reflect heat from the earth’s surface back towards the earth, so more carbon
dioxide in the atmosphere means that more heat will be trapped close to the earth’s surface and
temperatures on earth will rise. This disruption of the delicate balance in the composition of our
atmosphere is very dangerous because it causes global warming, which could have many
detrimental effects.
Classroom Resources
1. Make a Hot Air Balloon Activity
(Found at <http://www.ucar.edu/educ_outreach/webweather/tornact6.html>.)
In this activity, students create their own miniature hot air balloons out of tissue paper to
illustrate that warm air is not as dense as cold air and that warm air rises in the atmosphere,
which would be helpful in explaining convection currents.
2. Eyewitness – Weather Video
Eyewitness – Weather is a great classroom resource because it uses great detail and clarity when
explaining many weather concepts including wind, precipitation and storms, yet is still includes
attention-grabbing weather-related footage and remains targeted to a younger audience.
3. Ward’s Natural Science Catalog
Cajiga 5
(Found online at <http://www.wardsci.com/default.asp>.)
Precision Rain/Snow Gauge – This rain/snow gauge would be great to use in the classroom in
conjunction with other meteorology instruments such as barometers and thermometers to
conduct a lesson in which students record the daily weather conditions and make connections
between the information they collect.
Weather Wall Classroom Map – This large classroom map comes with movable
meteorologically-accurate weather symbols, which would help reinforce an understanding of
where different types of air masses come from and what the resulting weather conditions are.
The Weather Wizard’s Cloud Book – This book enhances knowledge of air masses and cloud
formations by providing students with full-color images of the many types of clouds and clearly
describing how each cloud forms, and what type of weather it suggests will occur.
Credits
I found this activity at both <http://www.lessonplanspage.com/Sciencecloudslesson.htm>
and <http://www.ucar.edu/educ_outreach/webweather/cloudact1.html>. The directions of the
activity described on each website varied slightly, so I combined the two and slightly modified
the wording to further clarify each step.