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WHERE DOES COOLED/HEATED AIR GO?

Parts of this are not good projects for people who suffer
respiratory problems. Just say "no," and find another way to
do the parts that could be harmful to health.

Make a tube of lightweight cardboard, and fit it loosely
around an uncovered light bulb. Turn the bulb on, and darken
the room. Hold two dusty chalkboard erasers near the bottom
of the tube and clap them together, and observe what happens.
The chalk dust will rise through the tube and go out the top.

What happens to the air that is warmed? It rises. What
happens to the air over warm parts of the earth? Warm air
creates a low pressure area.

Next, hold the tube under a tray of ice cubes and shine a
flashlight at the bottom of the cubes. Ask your teacher to
light a piece of clothesline rope or string on fire and hold
the smoking piece near the top of the tray. What happens to
the air as it is cooled? It falls.

What happens to the air over cold parts of the earth? Cooler
air forms a high pressure area and replaces warmer air as the
warmer air rises.

How does it help us to know that?

Air generally moves from a high pressure area to a low
pressure area. Thus, winds blow from high pressure areas to
low pressure areas. There are several activities that
help you realize this:

a. Hold two sheets of typing paper about 3 inches apart and
blow between them. As long as you blow, the sheets of
paper will be forced together because the rapidly moving
air current between the papers creates a low pressure
area as the greater surrounding pressure outside forces
the sheets of paper together.

b. Attach threads to two pingpong balls with clear tape or
drops of glue. Suspend the balls about 1 inch apart,
and, using a soda straw, blow between them. You will
realize that, as the stream of air passes between the
balls, a low pressure area results. This is indicated by
the balls' being pushed together.

Weather forecasters call low-pressure areas "lows" and high-
pressure areas "highs." If possible, study weather maps.
Indicate the high and low symbols. What do they mean in
terms of moving air masses?

How do circular wind patterns develop? What happens then?

I think we're going to find out what happens then.

This project definitely requires adult supervision.

Obtain a square-shaped hot plate and a cardboard box that is
at least 1 foot high and just slightly larger that the hot
plate. Cut the bottom from the box so that it can be set
over the hot plate. Cut out large openings on two adjacent
sides of the box, cover them with heavy clear plastic, cut a
4 inch hole in the top of the box, and paint the inside of
the box black.

Cut 1/2 inch slots in each of the four corners of the box.
The slots should start 1 inch from the top and extend to
within 1 inch of the bottom of the box. Now, fold a sheet of
lightweight cardboard 3 feet long and 17 inches wide to form
a cardboard chimney with 4 inch sides.

Tape the chimney along the side to hold it together, and
insert the chimney into the hole in the top of the box. Be
sure to tape the chimney securely, and seal it with melted
wax so that there are no air leaks.

Fill a shallow square tray about the same size as the hot
plate with water, and place it on the hot plate. Turn on the
hot plate. Place the box and chimney over the tray of water
and the hot plate.

Ask your teacher to shine a flashlight through one window,
so you can observe. You will see the formation of a vortex -
- like a miniature tornado -- above the boiling water.

A real tornado is formed similarly, due to convection
currents.

How do circular air currents start?

Spin a globe of the earth in a counterclockwise direction
(west to east), as viewed from above the North Pole. Try to
draw a straight line on the spinning globe by pressing
lightly on it with a piece of chalk or a wax pencil. The
line should extend from about 35 degrees North latitude to
the equator. When the globe stops spinning, observe the line
that was made.

The line could represent a wind blowing from the north. Such
winds are twisted to their right (west), as was the drawn
line. Because winds from the north constantly come in
contact with the earth's surface, whose speed of rotation is
greater than the speed of the winds, the wind currents lag
behind. This causes the winds to turn a little from their
straight course.

You will realize that the earth's rotation influences all
winds in the northern hemisphere, causing them to shift to
their right (i.e., north winds become easterly, and south
winds become westerly).

Winds which push toward a low pressure area are also twisted
to the right, creating a counter-clockwise swirl of air;
winds pushing out from a high pressure area are all twisted
to their right, creating a clockwise spiral of air.

This can be demonstrated 3-dimensionally by cutting a rubber
ball in half and painting rings around the outside of each
half. Place one cup of the ball open-side down on a map at a
place where a high pressure area might be indicated. Place
the other cup open-side up on the map where a low pressure
area might be. The cups represent air pressure areas.

Then, with a pencil, trace a path showing how the air will
spiral up one cup and spiral downward into the other.

Several more experiments can help you realize that heated air
rises and that cooler air falls to take its place:

Light a rope and blow out the flame. The rope will smoke.
Now, hold the rope a short distance above a candle flame and
away from other air currents. The smoke will travel upwards.

And I always thought that "smoke follows beauty!" [Why do
you think it is that people say that? What does it really
mean?]

This activity can be repeated over a hot radiator or an
electric hot plate, near an open refrigerator door, or at the
top and bottom of an open window.
Hold strips of aluminum foil above a lighted lamp chimney,
and observe what happens to the strips when they are dropped.
Repeat the activity near the base of the lamp chimney.

Here's more, just in case you like this particular group of
activities.

Various devices can aid in making observations of air
movements.

1. Cut a 6 inch square of paper. Fold the corners toward
the center. Put pinholes through the folded-over
corners. Suspend the pinwheel from a knotted thread.
Carry the pinwheel while you explore the room and the
school grounds looking for indications of rising and
falling air. Chart the air currents on a school map.
Several maps can be used to show the currents at
different times of day.

2. Cut a circle of paper about 6 inches in diameter, and
make a pinhole in the center. Cut the paper in a spiral,
and hang the spiral from a knotted thread. The spiral
can be held over a radiator or in other parts of the room
or schoolyard to locate and track the movements of air
currents.

3. Cut tissue paper in narrow 6 inch long strips. Attach
the strips to a stick or ruler with tacks, glue, or tape.
The stick can then be used in various locations to aid in
locating air movements.

Frankly, I think this is quite enough of this kind of fun.


 
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