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Investigation Question 1:
How can we see if water is in the air?
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What To Do
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Setting the Scene
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Show students a regular cloth hand towel. Tell them that you are thinking
about washing the towel, but, since there is no clothes dryer at the school,
you wonder how it might get dry. Ask them if they have an idea how you
could dry it (some students will eventually suggest hanging it out to
dry.) Ask the students where the water that makes the towel wet goes when
it is hung out and it dries (some students may indicate that the water
is simply "gone", while others may indicate that it is in the
air.) How can we see if water is in the air?
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Presenting the Investigation
Question
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Introduce your students to the investigation question: "How can
we see if water is in the air?"
Have your students discuss the question in pairs, then in groups, and then as a whole class. Record their answers on the flipchart.
Have your students brainstorm ideas about how this investigation question could be investigated.
- Design an experiment that could be used to test the investigation question.
- What materials would be needed?
- What would you have to do?
- What would be measured?
- How long would the experiment take?
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Assessing What Your Students Already Know
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When asked to describe a cloud, most students will portray a remote,
white fluffy object in the sky, much like a floating cotton ball. Some
students who have had experiences with air travel might be able to describe
flying above the clouds or into clouds. Few children will think that they
have ever touched a cloud or walked through a cloud.
- Ask your students if they have ever been in fog. (They might be surprised
to know that fog is a cloud at ground level.)
- If you live in a climate with cold temperatures, ask if they have
ever seen their breath on a cold morning. (If so, they have actually
created clouds.)
- Ask your students if they have noticed that fog or breath seems to
be wet or damp. (What they are seeing is a collection of tiny water
droplets that form as water vapor turns to liquid.)
Tell your students that in this investigation they will learn how to
tell that there is water in the air.
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Exploring the Concept
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1.
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Give each group of students a metal cup or glass tumbler. Ask them
if the cup appears to be able to hold water without leaking any
to the outside. (You might fill yours with room temperature water
to verify that it is leak-free.)
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2.
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Pour an amount of room-temperature water into the cup, leaving
room for several ice cubes that will be added next. (It is best
to have a pitcher or bowl of water sitting in the room for several
minutes before beginning, to ensure that the water will not be cooler
than the air in the room.) Have students verify that the cup
is not leaking. If there is any water on the outside of the cup
due to spills, have them dry it off and check again for leaks.
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3.
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Next, distribute the ice into the cup of water so that all cups
are about half-filled.
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4.
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Ask the students to observe the cup carefully for a few minutes
and record their observations. (The outside of the cup will begin
to show drops of water on the surface. If the room is exceptionally
dry, ask the students to blow on the side of the tumbler. Moisture
from their breath will condense on the surface.)
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5.
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Have your students discuss their observations and these questions:
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- What have you seen form on the outside of the cool cup or
glass tumbler? (Tiny water droplets.)
- How can you be sure what it is? (It's wet, and it feels
and looks like water.)
- Where do they think it came from? (Some might connect it
to the water in the tumbler. If they do so, remind them that
the tumbler was tested before the experiment and found to be
leak-free.)
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6. |
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Ask your students to report their conclusions about their observations
of the ice-filled container to the class. (Through careful discussion
and questioning, your students should be able to agree that the
only place the water could have come from was the air.)
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7.
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Help your students focus on what they have learned. They should
be able to figure out that the air contains water that is invisible.
But, when the air is cooled, the invisible water in the air forms
liquid water on a surface. Finally, introduce your students to the
scientific term for this process - condensation.
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