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The Earth is surrounded by a layer of air called the atmosphere. The air in the
atmosphere has weight, and it's pressing down on the Earth all the time. This
pressure is called air pressure. Changes in air pressure are measured with a very
sensitive instrument called a barometer.
Meteorologists pay close attention to air pressure. That's because changes in air
pressure bring changes in weather. High air pressure signals clear skies and mild
weather. Low air pressure brings cloudy, rainy weather. What kind of air pressure do
you think you'd find in the center of a tornado or hurricane?
Build your own barometer to measure air pressure. Then try making your own forecast based on the changes
in air pressure you observe.
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- Small coffee can
- Plastic wrap
- Scissors
- 2 straws (one flexible and one
straight)
- Ruled index card
- Rubber band
- Clear tape
- Printout of your Weather
Chart
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Cover the top of the can with
plastic wrap like the top of a
drum. Use a rubber band to
hold the plastic wrap in place.
The cover should be tight so
air cannot escape the can. |
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Bend your flexible straw into
an L-shape. Lay the longer
part of the straw over the
plastic wrap so that the end
of the straw is on the middle
of the can, and the bent part
is hanging over the side of the
can (the straw needs to be
level with the top of the can).
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Tape the straw to the middle
of the plastic wrap.
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Place the end of the straight
straw lengthwise to the
middle of the index card.
Tape them together. Then
tape the other end of the
straw towards the top of the
side of the can.
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Place your barometer on a table or flat surface. Make sure it's inside and
not near a window, since it might be affected by temperature. |
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Carefully record the height
of the straw on the index
card. Mark it with a marker
and put the number 1 on it.
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After 30 minutes, record
the new location of the straw
on the index card with the number 2.
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Keep checking back to see if the straw has moved. Each time, mark the index
card to show the straw's new location. It's best to make these measurements
for at least half a day. |
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The straw moves up and down as the air pressure changes.
| If the straw's tip moves up, that means the air pressure is increasing. The
plastic wrap depresses with higher pressure, thus raising the straw's tip. High pressure usually means the weather will be clear and
pleasant. |
| If the straw's tip moves down, that means the air pressure is falling. Under low pressure, the plastic wrap relaxes and would even rise
because of the build-in pressure inside the can, thus lowering the
straw's tip. Low pressure
usually means that cloudy or rainy weather is on the way. |
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Determine whether the air pressure is rising or falling. Then record the date
and your findings in your Weather Chart. |
