Air - something or nothing?
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Rationale/Objectives/Purpose:
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To demonstrate that air is matter.
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Time Required:
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Teacher Prep- 15 minutes to gather materials.
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Teacher Demonstration- 15 minutes.
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Safety Issues:
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Be prepared to clean up any spilled water to avoid slips and falls.
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Materials:
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A large (1-3 gallon) glass container
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A pickle jar from the cafeteria works if it has a wide mouth, or a ten
gallon aquarium, or a battery jar.
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A small clear glass.
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A dollar bill, or a hundred dollar bill.
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Procedures:
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Teacher- Fill the large container with water. Hold up the glass to the
class and ask as you turn it upside down, "What's in this glass?" Some
may answer "Air" some may answer, "Nothing". Point out to the class that
some people say air and some say nothing. Ask, "Is there a difference between
the two answers, or is 'air' what we say when there is really nothing there.
In other words is air something or is air nothing."
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Now procede to propose a 'proof' of the existence of air. Put the dollar
bill firmly in the bottom of the dry glass, put in snug enough so that
it won't fall out. Hold the glass upside down and slowly submerge it into
the large container of water. As you begin, explain that if there is nothing
in the glass, water will enter and get the dollar wet. If air is 'something'
and it can't get out, it will keep the water out and the dollar will stay
dry.
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Assessment:
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One assesment may turn out to be your own surprise at the number of
middle school students who are awed by this simple demonstration.
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Extensions/ Background:
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Students can do this in groups of two. You may want to precede or follow
this with a definition of matter, "Anything that takes up space and has
mass." That may lead to weighing a ballon empty, blowing it up and reweighing
it, popping it and weighing it a third time. All to demonstrate logically
that air has mass (weighs something on earth). FYI- The weight of a room
full of air is about 100 pounds. All this leads into the next activities
on air pressure.
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Air pressure relates to El Niño - differences in air pressure
cause the trade winds, which blow from areas of high pressure to areas
of low pressure. The prevailing direction of trade winds is from
the eastern equatorial Pacific (high pressure) towards the western equatorial
Pacific (low pressure). Oscillations occur when the pressure in the eastern
Pacific decreases, and the pressure in the western Pacific increases. This
causes a diminishing or reversal of the trade winds.
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Furthermore, the winds blow the water. The warmer water on top of the
ocean is usually moved whichever way the winds blow. During a normal year,
the warmer surface water is mainly in the western Pacific because of the
trade winds. During an El Niño event, however, the warmer water
is moved eastward. (During a La Niña event, the warmer water is
moved further westward). Wherever the warmer water is, you typically get
more rain because warmer water evaporates more easily. During an
El Niño event, the colder, nutrient-rich water beneath the abnormally
abundant warm water by South America is not readily brought up to the surface
as it is in a normal year. Keep in mind that fish like the colder
water because it's loaded with nutrients, and in a normal year, the South
American coast near Peru boasts of a high fish productivity. However,
in an El Niño more warm water sloshes over to the South American
coast so fish productivity tends to decline.