Answer:
Explanation: Water is arguably the most
important resource on our
Earth. We depend upon
water to survive and are intimately tied to
tiny water molecules cycling through our
world. Throughout history, the locations
in which cities and entire civilizations
have developed have been influenced by
the location and abundance of freshwater
resources. We have come to depend
upon seasonal rains, snowmelt from
mountains, and water recharging our
underground reservoirs.
This chapter covers the processes by
which water moves around Earth, and
the forms water takes on its journey
through the water cycle. Although this
cycle receives a great deal of attention
in our schools, students still struggle
to understand many of the most basic
concepts about the water cycle. We
explore some of these difficult concepts
in more depth and emphasize that
throughout their learning of these
concepts, it is critical that students
come to understand that no new water
is created during the water cycle—all of
our water on Earth is recycled—and that
there is a limited amount of freshwater
available in the world.
The Water Cycle
As water moves around Earth, it does so
as part of what we call the water cycle.
The water cycle is one of the most iconic
topics taught to students during the
upper elementary and middle school
years. Most of Earth’s water is present
in the ocean. As the sun shines on the
water, it heats the water and causes it to
evaporate. Note that evaporation is not
only caused by heat from the sun, but
is also influenced by wind and surface
area, as well as other factors. As each
molecule of water on the surface of the
ocean evaporates into the air, it pulls
another water molecule to the surface.
Now this next molecule of water is
exposed to the heat and drying effects
of the air, and it also will evaporate.
As the water molecules evaporate, the27
CHAPTER OVERVIEW In the Classroom:
Surface Tension 32
Student Thinking:
Water-Cycle Processes 34
Pictures of Practice:
Learning About Evaporation 35
In the Classroom:
Cloud in a Bottle 36
Student Thinking:
What Makes up a Cloud? 37
Representations of Science:
The Water-Cycle Journey 38
Student Thinking:
Groundwater 40
Student Thinking:
Watersheds and Rivers 47
In the Classroom:
Splish, Splash: Water’s
Journey to My Glass 48
Case Study:
The Urban Water Cycle 49
Pictures of Practice:
The Urban Water Cycle 52
Water is all over the world! It is in the atmosphere, underground, running
across Earth’s surface, and even in the bodies of organisms. Some water
moves quickly from one place to another, such as the water that is moving
down rivers into oceans or the water at the surface of the ocean that
evaporates into the sky. Some water may be trapped below Earth’s surface,
unable to move or evaporate for millions of years.
In order to know where we can find freshwater and how to keep it clean,
we need to understand where water is located on Earth and how it may
move from one place to another. This chapter outlines the water cycle by
discussing not only how water moves from one reservoir to another, but
also the challenges students typically need to overcome to understand this
complex system.
In addition, this chapter explores concepts that students typically struggle
to understand, such as groundwater and watersheds. The chapter
concludes with an in-depth look at the urban water cycle in comparison to
the natural water cycle.
minerals or salts that they may have
been carrying are left behind in the
salty ocean. During this process, the air
becomes more and more humid. This
water vapor is an invisible gas and can
move quickly. As it moves about, it often
travels upward or inland—carried by
currents in the air (wind).
As the moister air gains elevation, the
molecules become colder and condense,
turning into liquid. As more and more
of these water molecules condense,
they cluster around particles (primarily
suspended dust) in the atmosphere and
form clouds. Students may be confused
if clouds are gas or liquid. However,
a cloud is comprised of liquid water
droplets, which is why one can see them,
as compared to the water vapor, invisible
gaseous water molecules suspended in
the atmosphere.
When the mass of water molecules is
high enough, the clouds will dispense
their contents as precipitation.
Precipitation can occur as rain or snow
or ice, depending on surrounding air
temperature.