sx05_NCGR8_ch02CNEW.fm Page 80 Wednesday, June 8, 2005 4:13 PM
6
Section
6
Water
Underground
Reading Preview
Objectives
After this lesson, students will be able to
H.2.4.1 Describe how water moves through
underground layers of soil and rock.
H.2.4.2 Explain how people obtain water
from an aquifer.
Key Concepts
• How does water move through
underground layers of soil and
rock?
• How do people obtain water
from an aquifer?
Key Terms
Target Reading Skill
Previewing Visuals Explain that looking at
the visuals before they read helps students
activate prior knowledge and predict what
they are about to read.
Answers
Possible answers:
What is an artesian well? (It is a well in
which water rises because of pressure within
an aquifer.) Where does the water that
supplies a well come from? (Underground
water comes from precipitation that trickles
down between particles of soil and through
cracks and spaces in layers of rock.)
• permeable • impermeable
• saturated zone • water table
• unsaturated zone • aquifer
• artesian well
Target Reading Skill
Previewing Visuals Before you
read, preview Figure 29. Then
write one question that you have
about the diagram in a graphic
organizer like the one below. As
you read, answer your question.
Bringing Up Groundwater
Q. What is an artesian well?
A.
Q.
Teaching Resources
• Transparency H11
Where Does the Water Go?
1. Add pebbles to a jar to form a layer about
5 centimeters deep. Cover the pebbles with
a layer of dry sand about 3 centimeters
thick. Pour the sand in slowly to avoid
moving the pebbles. These materials
represent underground soil layers.
2. Sprinkle water onto the sand to simulate rainfall.
3. Looking through the side of the jar, observe the path of the
water as it soaks through the layers. Wash your hands when
you are finished with this activity.
Think It Over
Observing Describe what happened when the water reached
the bottom of the jar.
When you were a little child, did you ever dig a hole in the
ground hoping to find a buried treasure? You probably never
found a trunk full of gold. But there was a certain kind of treasure hidden underground. If you had dug past the tangled
grass roots and small stones, the bottom of your hole would
have filled with water. You would have “struck groundwater!”
In the days before public water systems, water underground
was truly a hidden treasure. Today, many people still rely on
the water underground to meet their water needs.
How Water Moves Underground
Preteach
Build Background
Knowledge
Water Underground
Where does this underground water come from? Like the water
in rivers, lakes, and glaciers, it comes from precipitation. Recall
that precipitation can evaporate, run off the surface, or soak
into the ground. If water soaks into the ground, it trickles
downward, following the pull of gravity.
If you pour water into a glass full of pebbles, the water
trickles down around the pebbles until it reaches the bottom of
the glass. Then the water begins to fill up the spaces between
the pebbles. In the same way, water underground trickles
down between particles of soil and through cracks and
spaces in layers of rock.
L1
Sources of Water
Show the class a bottle of spring water you
have purchased. Ask: What was the original
source of this water? (Students may mention
wells, springs, or other sources.) Where does
the water in springs come from? (Students
may be unsure or may suggest an underground
supply. Some may know the term “aquifer.”)
Acknowledge responses without comment at
this time.
80 ◆
L1
Skills Focus observing
Materials pebbles, clear jar, ruler, dry
sand, water
Time 10 minutes
Tips Using a plastic jar avoids the danger
of broken glass. Advise students to add the
water slowly.
80
Expected Outcome The water will seep
through the sand and collect at the bottom
of the jar.
Think It Over The water filled the spaces
between the pebbles.
sx05_NCGR8_ch02CNEW.fm Page 81 Wednesday, June 8, 2005 4:13 PM
Effects of Different Materials Different types of rock
and soil have different-sized spaces, or pores, between their
particles, as shown in Figure 28. The size of the pores determines how easily water moves through rock and soil. If the
pores are connected, this too affects water movement. Because
they have large and connected pores, materials such as sand
and gravel allow water to pass through, or permeate. They are
thus known as permeable materials.
As water soaks down through permeable rock and soil,
it eventually reaches layers of material that it cannot pass
through. These materials have few or no pores or cracks.
Two examples are clay and granite. Clay and granite are
impermeable, meaning that water cannot pass through easily.
Instruct
How Water Moves
Underground
For: Links on water underground
Visit: www.SCiLinks.org
Web Code: scn-0815
For: Links on water
underground
Visit: SciLinks.com
Web Code: scn-0815
Download a worksheet that will guide students’ review
of Internet resources on water underground.
Water Zones Once water reaches an impermeable layer, it is
trapped. It can’t soak any deeper. Instead, the water begins to fill
up the spaces above the impermeable material. The area of permeable rock or soil that is totally filled, or saturated, with water
is called the saturated zone. The top of the saturated zone is the
water table. If you know the depth of the water table in your
area, you can tell how deep you must dig to reach groundwater.
Soil and rock layers above the water table contain some
moisture, too. But here the pores contain air as well as water.
They are not saturated. Therefore, the layer of rocks and soil
above the water table is called the unsaturated zone.
Give an example of a permeable material.
Teach Key Concepts
Water Moves Through Soil and Rock
Focus Remind students that groundwater
supplies most of the available fresh water
on Earth.
Teach Refer students to Figure 21. Point out
that when the water seeps into the ground
and reaches an impermeable layer, the water
stops sinking because the rock layer is made
up of materials that have few open spaces for
absorbing water. Ask: How does water fill
up spaces underground? (It trickles down
between particles of soil and through cracks
and spaces in layers of rock.) What is the term
for the kinds of materials through which
water can pass? (Permeable)
Apply Ask students to find the average
water table depth in your community.
FIGURE 28
Groundwater Formation
Differences in the materials that
form layers underground
determine where groundwater
forms. Water can move through
certain layers but not others.
Interpreting Diagrams What is the
saturated zone? Where is it
located?
Unsaturated
zone
Permeable
layers
L2
learning modality: logical/mathematical
Water table
Teaching Resources
Saturated
zone
Impermeable
layer
• Transparency H12
Solid rock
Air
Water
Independent Practice
Unconnected
pores
Teaching Resources
• Guided Reading and Study Worksheet:
Water Underground
Student Edition on Audio CD
Chapter
◆ 81
2
Monitor Progress
Differentiated Instruction
L1
English Learners/Beginning
Contrast
Vocabulary: Word Analysis
the meanings of permeable and
impermeable. Point out that the prefix
im- sometimes means “not,” and that
words with this prefix may mean the
opposite of the word without the prefix.
Explore the meanings of saturated and
unsaturated. learning modality: verbal
L2
English Learners/Intermediate
Vocabulary: Word Analysis Have
students find the derivation of aquifer
in the dictionary. (From the Latin word
aqua, meaning “water”) Ask students
to think of other English words that
contain the root word aqua. (Examples:
aquarium, aquamarine, aquatic, and
aqueduct.) learning modality: verbal
L2
L2
Drawing Have students draw a simple
sketch of an underground water supply
without referring to Figure 21.
Answers
Figure 21 The area of permeable rock or
soil that is totally filled; between the water
table and solid rock
Possible answers: soil;
porous rock, such as
sandstone; materials such as foam rubber,
plastic foam, and cloth
81
sx05_NCGR8_ch02CNEW.fm Page 82 Wednesday, June 8, 2005 4:13 PM
Bringing Up Groundwater
Bringing Up
Groundwater
Teach Key Concepts
Suppose you live far from a city, town, or body of fresh water.
How could you reach groundwater to use it for your daily
needs? You may be in luck: the water table in your area might
be only a few meters underground. In fact, in some places the
water table actually meets the surface. Springs can form as
groundwater bubbles or flows out of cracks in the rock. A short
distance away, the water table may be deep underground.
L2
How People Obtain Water
From an Aquifer
Focus Review with students the water zones
found under Earth’s surface—the saturated
zone, the unsaturated zone, and the water
table.
Teach Call attention to the two wells in
Figure 22. Ask: Why is one well dry? (The
well does not reach the water table.) How can
people obtain water from an aquifer? (They
can use mechanical equipment to obtain
groundwater from an aquifer by drilling a well
below the water table.) Why is the water
from the artesian well spurting up? (The
water at the bottom of the aquifer is under
pressure from the water at the top of the
aquifer.) Ask: Why might the level of the
water table vary? (The water follows the
shape of the underground rock layers.)
Apply Ask: Why might the variations of
the level of water in the water table cause
people to get water in their basements?
(During heavy rains, the water table could
rise to the surface.) learning modality:
logical/mathematical
Aquifers Any underground layer of rock or sediment that
holds water is called an aquifer. Aquifers can range in size from a
small underground patch of permeable material to an area the
size of several states. The huge Ogallala aquifer lies beneath the
plains of the Midwest, from South Dakota to Texas. Millions
of people obtain drinking water from this underground storehouse. The aquifer also provides water for crops and livestock.
Do you picture groundwater as a large, still pool beneath
Earth’s surface? In fact, the water is moving, seeping through
layers of rock. The rate of movement depends largely on the
slope of the aquifer and the permeability of the rocks. Groundwater in some aquifers moves only a few centimeters a day. At
that rate, the water moves about 10 meters a year. Groundwater may travel hundreds of kilometers and stay in an aquifer for
thousands of years before coming to the surface again.
Water Use in the United States
Uses of Water
The graph shows water use in the United
States. Each category of water use is
represented by a different color. Use the graph
to answer the questions below.
Industries
and Mining
9.1%
Households and
10.4%
Businesses
Agriculture
41.8%
1. Reading Graphs How many categories of
water use are shown on the graph?
Math Skill Making and interpreting graphs
Focus Point out that a circle graph shows
parts of a whole.
Teach Explain how to calculate the answer
to the fifth question by converting the
percentage used by power plants to a decimal
and then multiplying by the total number of
liters. (1,280 billion × 0.387 = 495 billion)
Answers
1. 4
2. 80.5%
3. Agriculture; industries and mining
4. The percentage for agriculture would
increase, and the percentage for all of the
other uses would decrease.
5. About 495 billion liters
82
2. Interpreting Data The two largest categories
of water use combine to make up about
what percentage of the total water used in
the United States?
3. Interpreting Data Which of the categories of
water use shown in the graph represents the
largest use of water in the United States?
Which represents the smallest?
4. Predicting How would an increase in the
number of farms affect this graph?
82 ◆
Power
Plants
38.7%
5. Calculating If the total daily usage of water
in the United States is 1,280 billion liters,
about how many liters are used each day by
power plants?
sx05_NCGR8_ch02CNEW.fm Page 83 Wednesday, June 8, 2005 4:13 PM
Help Students Read
Artesian Well
Water rises when rock above
an aquifer is punctured.
Spring
Groundwater that flows to
the surface is called a spring.
Aquifer
Well
A channel dug into
the aquifer provides
a supply of water.
Dry Well
When the level of
an aquifer drops,
a well can run dry.
L2
Aquifer
Water
Table
Impermeable Rock
Aquifer
Wells The depth of a water table can vary greatly over a small
area. Its level may vary as well. Generally, the level of a water
table follows the shape of underground rock layers, as shown
in Figure 29. But it can rise during heavy rains or snow melts,
and then fall in times of dry weather. So what do you do if the
depth and level of the water table in your area is far underground? How can you bring the water to the surface?
Since ancient times, people have brought groundwater to
the surface for drinking and other everyday uses. People can
obtain groundwater from an aquifer by drilling a well below
the water table. Locate the well near the center of Figure 29.
Because the bottom of the well is in a saturated zone, the well
contains water. Notice the level of the bottom of the dry well in
the diagram. Because this well does not reach below the water
table, water cannot be obtained from it.
FIGURE 29
Springs and Wells
Sometimes underground water
comes to the surface naturally.
Other times, people use energy
to obtain groundwater.
Comparing and Contrasting How
do the ordinary well, artesian well,
and dry well differ?
Materials jar, sand, gravel, large rocks, water
Time 15 minutes the first day; 5 minutes
the next
Teach Have students fill a jar with a mixture
of sand, gravel, and rocks, and then slowly
pour water into the jar and wait a few
minutes. Students mark the level of the water
with tape or a grease pencil. Let the jars sit
for one day, and then observe the level of
the water. The water level in the jars should
be lower.
Apply Ask: What is the boundary between
the saturated and unsaturated zones in
your jars called? (The water table) Why do
you think the level of the water table
changed? (Water evaporated from the soil.)
Teaching Resources
• Transparency H13
Chapter 2
◆ 83
Monitor Progress
L2
Drawing Have each student draw diagrams
showing an underground dry well and a
working well.
Differentiated Instruction
Less Proficient Readers
Understanding Water Underground
Provide students with the section on
Student Edition on Audio CD and a copy
of the passage Bringing Up Groundwater.
Have them listen to this passage as they
read along and highlight key phrases and
Modeling the Water Table
Focus Review with students how water
moves underground.
learning modality: visual
Why might a water table rise? Why might a water
table fall?
L1
L2
Predicting Refer to the Content Refresher
for guidelines on predicting. Tell students to
examine Figure 22. Ask them to make a
written prediction about how water might
flow from an artesian well, based on what
they know about aquifers, the flow of
underground water, and water pressure.
After they have finished reading the section,
have them write a response to the prediction,
correcting any misconceptions and adding
details.
sentences that explain the different ways
that groundwater can be obtained. Then
pair students with more proficient readers.
Have each pair construct a concept map
that includes and defines the terms aquifer,
artesian well, spring, and geyser. learning
modality: verbal
Answers
Figure 22 The ordinary well extends below
the water table, so water can be pumped to
the surface. The dry well does not reach the
water table and cannot provide water.
Pressure causes water to spurt from an
artesian well without having to be pumped.
The water table rises after
rain or melting snow sink
into the ground. The water table falls after a
period of dry weather.
83
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L1
Modeling a Geyser
Materials teakettle, hot plate
Time 10 minutes
Focus Review the definition of a geyser.
Teach CAUTION: Wear
goggles and heat-resistant
gloves while performing this demonstration.
Heat some water in a teakettle on the hot
plate. When the water boils and the kettle
releases steam, ask: What would happen if
I plugged the kettle’s spout? (The pressure
of the steam would build up to a point at
which it would blow the plug out of the spout.)
CAUTION: Do not try this. Emphasize that
this is what happens in a geyser. Ask: What
supplied the heat to boil the water in the
kettle? (The hot plate, electricity, electrical
energy)
Apply Ask: What do you think heats water
underground? (Possible answers: magma,
molten rock, lava, or hot rocks.) learning
modality: logical/mathematical
An Artesian Well
For this activity, cover your
desk with newspaper.
1. Cover the bottom of a loaf
pan with clay. Pile the clay
higher at one end. Cover
the clay with about 4 cm
of moist sand.
2. Cover the sand with a thin
sheet of clay. Seal the
edges of the clay tightly
against the pan.
3. Push a funnel into the
high end so the bottom of
the funnel is in the sand.
4. Insert a short piece of
plastic straw through the
clay and into the sand
layer at the low end.
Remove the straw, discard
it, and then insert a new
piece of straw into the
same hole.
5. Slowly pour water into the
funnel. Do not let the
water overflow.
6. Observe the level of water
in the straw.
Making Models How is your
model like a real artesian
well? How is it different?
Using Pumps Long ago, people dug wells by hand. They
lined the sides of the well with brick and stone to keep the
walls from collapsing. To bring up the water, they lowered and
raised a bucket. People may also have used simple pumps, like
the one shown in Figure 30. Today, however, most wells are
dug with well-drilling equipment. Mechanical pumps bring up
the groundwater.
Pumping water out of an aquifer lowers the water level near
the well. If too much water is pumped out too fast, a well may
run dry. The owners of the well will have to dig deeper to reach
the lowered water table, or wait for rainfall to refill the aquifer.
New water that enters the aquifer from the surface is called
recharge.
Relying on Pressure Now you know how to bring groundwater to the surface. But what if that didn’t work? You might
not be out of luck. You might be able to drill an artesian well.
In an artesian well (ahr TEEZH un), water rises because of
pressure within an aquifer.
Look back at Figure 29 and locate the artesian well. In some
aquifers, groundwater becomes trapped between two layers of
impermeable rock or sediment. This water is under great pressure from the weight of the rock above. If the top layer of rock
is punctured, the pressure sends water spurting up through the
hole. No pump is necessary—in an artesian well, pressure does
the job.
FIGURE 30
Working for Water Here a resident
of Bangladesh uses a hand pump to
bring groundwater to the surface.
Interpreting Photographs What is
one disadvantage of a hand pump?
84 ◆
L2
Skills Focus Making models
Materials newspaper, loaf pan, modeling
clay, moist sand, funnel, plastic straw,
scissors, water
Time 20 minutes
Tips Before students begin, add a little
water to the sand. Make extra clay available
to stop any leaks and have paper towels
available to remove water that overflows.
84
Expected Outcome Water will flow from
the funnel into the sand layer at the high
end, downhill through the sand layer,
and up the straw at the low end. The clay
and sand represent impermeable and
permeable layers. The water represents
precipitation. The flow of the water
downhill represents real water movement
in an aquifer. The model is like a real
aquifer in that water moves through a
permeable layer. It is different because
water would fall as precipitation and soak
through permeable material until it
reached a layer of impermeable rock.
Extend Ask: What would happen if you
cut the straw below the water level of the
funnel? (Doing so would produce a gushing
artesian well.) learning modality:
kinesthetic
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Springs and Geysers Sometimes, groundwater comes
to the surface through natural processes. You read that
places where groundwater bubbles or flows out of cracks
in the rock are called springs. Most springs contain water
at normal temperatures. Others, like those in Figure 31,
contain water that is warmed by the hot rocks deep below
the surface. The heated water bubbles to the surface in
hot springs.
In some areas, you might see a fountain of boiling hot
water and white steam burst into the air. This is a geyser,
a type of hot spring from which the water periodically
erupts. The word geyser comes from an Icelandic word,
geysir, which means “gusher.”
A geyser forms when very hot water that has been circulating deep underground begins to rise through narrow
passages in the rock. Heated gases and bubbles of steam are
forced up these passages by the pressure of the hot water
boiling below. Just as pressure builds up in a partly blocked
water pipe, the pressure within these narrow openings in
the rock increases. Finally, the gases, steam, and hot water
erupt high into the air.
Monitor Progress
Answers
Figure 23 Answers may vary. Sample
answer: Water can be collected only when
there is someone available to operate the
hand pump.
A geyser is formed by heated
groundwater. The heated
water, gases, and steam erupt as a result of
the buildup of pressure.
FIGURE 31
A Hot Spring
A Japanese macaque takes advantage
of the warm water that rises to the
surface of a hot spring in Nagano,
Japan.
How do geysers form?
6
Section 5 Assessment
Target Reading Skill Previewing Visuals
Refer to your questions and answers about
Figure 29 to help you answer Question 2 below.
Reviewing Key Concepts
1. a. Reviewing What happens to water in the
ground when it reaches impermeable
materials?
b. Explaining What two factors determine
how easily water can move through
underground materials?
c. Inferring Would an impermeable material
have large or small pores? Would the pores
be connected or unconnected? Explain.
2. a. Describing How can people obtain water
from an aquifer?
b. Interpreting Diagrams Using Figure 29 as a
guide, explain why is it important to know
the depth of an aquifer before drilling a well.
L2
c. Problem Solving During the winter, you
draw your water from a well on your
property. Every summer, the well dries up.
What might be the reason for the change?
Formal Letter Water usage in your town has
risen in recent years due to population
growth. Your town obtains its water from a
nearby aquifer. You are concerned that the
water level of the aquifer may be going
down. Write a letter to local government
officials explaining your concerns. Describe
the effect of heavy water usage on the
aquifer and suggest measures that can be
taken to avoid a water shortage.
Chapter 2
◆ 85
Assess
Reviewing Key Concepts
1. a. It is trapped, forming a water table.
b. The size of the pores of underground
materials and whether the pores are
connected c. Impermeable material would
have small pores that would not be
connected. Water could not move as easily
through small pores that are not connected.
2. a. They can use mechanical equipment to
drill a well below the water table. b. Without
knowing the depth of the aquifer, drillers
don’t know how deep to drill the well to be
below the water table. c. The water table
must fall below the level of the well in
summer and rise above it in winter. Factors
such as precipitation and human water use
could also affect the depth of the water table.
Reteach
L1
Summarize the connection between
saturated and unsaturated zones and
permeable and impermeable layers of
material beneath Earth’s surface.
Performance Assessment
Drawing Have each student draw a simple
sketch of the artesian well model that he or
she made in the Try This Activity. Ask
students to add labels and captions that
explain how a real artesian well works.
Teaching Resources
• Section Summary: Water Underground
• Review and Reinforce: Water Underground
• Enrich: Water Underground
Writing Skill Persuasion
Scoring Rubric
4 Exceeds criteria by including four or five
well-thought-out measures and a convincing
argument
3 Meets criteria and includes two or three
measures
2 Includes only a brief explanation and one
or two measures
1 Is incorrect and incomplete
85
sx05_NCGR8_ch02CNEW.fm Page 86 Wednesday, June 8, 2005 4:13 PM
Soil Testing
L2
Prepare for Inquiry
Key Concept
Different soil materials have different
permeabilities.
Skills Objectives
Students will be able to
• observe the flow of water through various
materials
• develop a hypothesis to compare the flow
of water through different materials
• design an experiment to test their
hypothesis
Class Time 40 minutes
Teaching Resources
• Lab Worksheet: Soil Testing
Alternative Materials
If funnels are not available, cut the tops off
plastic soda bottles, or let students do this.
Have them cover the rough edges with
masking tape to avoid cutting themselves.
Safety
Have students wear safety goggles.
Review the safety guidelines in
Appendix A.
Guide Inquiry
Invitation
After distributing the sand, clay, and pebbles,
have students look at and feel these items.
Ask: Which material would let water pass
through most quickly? Which material do
you think would hold water best? Write the
hypotheses on the board, and discuss these
responses when students complete the lab.
Soil Testing
Material Observations
Problem
How fast does water move through sand, clay,
and pebbles?
Time for Water
to Stop Dripping
Sand
Clay
Pebbles
Skills Focus
observing, developing hypotheses, designing
experiments
Suggested Materials
• hand lens
• 100 mL of sand
• stopwatch
• 3 rubber bands
• 3 100-mL beakers
• 300 mL of water
• 100 mL of pebbles
• 100 mL of powdered
potter’s clay
• 3 squares of
cheesecloth
• 3 large funnels or cutoff plastic bottle
tops
Procedure
PART 1 Observing the Flow of Water
Through Sand
1. Copy the data table in your notebook.
2. Use a hand lens to observe the sand sample
closely. Record your observations in your
data table.
3. Place a piece of cheesecloth over the bottom
of one funnel or bottle top and secure it
with a rubber band.
4. Place the sand in the funnel. Be sure that
there is about 5 cm of space above the sand
in the funnel.
5. Place the funnel on top of a beaker.
6. Slowly pour 100 mL of water into the funnel.
Do not let the water overflow the funnel.
7. Start the stopwatch when the water begins
to flow or drip out of the funnel.
8. Stop the stopwatch when the water stops
dripping out of the funnel or after 5 minutes. Record the time to the nearest second
in your data table.
PART 2 Comparing the Flow of Water
Through Different Soil Samples
9. Use a hand lens to observe each of the two
other material samples closely. Record your
observations in the data table.
10. Using the procedures you followed in Part 1,
design an experiment to compare the flow
of water through sand, clay, and pebbles. Be
sure to write a hypothesis and to control all
necessary variables.
11. Submit your experimental plan to your
teacher. After making any necessary changes,
carry out your experiment. Record your
observations in your data table.
12. When you are finished with this activity,
dispose of the materials according to your
teacher’s instructions. Wash your hands
thoroughly with soap.
86 ◆
Introduce the Procedure
• Ask: Which would be a good location
for a well—in soil that lets water pass
through easily, or in soil that does not
let water pass through? (Soil that lets
water pass through easily)
86
Data Table
• After students read through the procedure,
ask: Why should the layers of sand, clay,
and pebbles be the same depth? (The
depth is a variable that should be controlled;
making the layers different depths could
affect the results.)
sx05_NCGR8_ch02CNEW.fm Page 87 Wednesday, June 8, 2005 4:13 PM
Troubleshooting the Experiment
• In Step 1, suggest that students make the
Observation section of their table larger
than the others so that they have more
room to record.
• If necessary, demonstrate how to make
sure the beaker is filled exactly to the 100mL mark in Step 6. Also remind students
to stop pouring the water if it comes close
to overflowing the funnel.
Expected Outcome
Times will vary. Sample data may show that
it takes about 9 minutes for 100 mL of water
to flow through sand, 2 minutes to flow
through pebbles, and 15 minutes to flow
through clay.
Analyze and Conclude
5. Predicting Based on the results of this lab,
would you expect to get more water from a
well dug in sand, pebbles, or clay? Explain.
1. Observing In Part 1, how did the sand look
under the hand lens? How long did it take
the water to flow through the sand?
6. Communicating You and your neighbor are
discussing your gardens. You’re explaining
that it’s important for a gardener to know
the permeability of different soils. Write
your conversation in dialogue form. Use
quotation marks for each speaker.
2. Developing Hypotheses What hypothesis
did you test in Part 2? On what did you base
your hypothesis?
3. Designing Experiments What was the
manipulated variable in Part 2? What was
the responding variable?
4. Drawing Conclusions Through which material did water move the fastest? The slowest?
What can you conclude about the permeability of the three materials?
More to Explore
Of the soil samples you tested, which do you
think most resembles the soil on the grounds at
your school? Explain your reasoning. How might
you test your hypothesis?
Chapter 2
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Analyze and Conclude
1. Possible answer: The sand was composed
of small grains, had irregular shapes, and
was colored white, tan, and brown; answers
will vary but should be less than the time for
flowing through the clay and more than the
time for flowing through the pebbles.
2. Possible answer: Water will flow fastest
through pebbles. It will flow more slowly
through sand and slowest through clay.
The hypothesis was based on the size of
the particles.
3. The size of the particles was the
manipulated variable. The rate of water
flow was the responding variable.
4. It moved fastest through pebbles, and
slowest through clay. Pebbles are the most
permeable; clay is the least permeable.
5. You would get more water from a well dug
in pebbles because there are larger pores that
can hold more water, and the water moves
quickly through the pebbles and into the well
as water is pumped out.
6. Students’ dialogues should include that
some plants may survive and grow best in
sandy soils that let water drain away from
their roots, whereas other plants grow best
in clay soils that hold water.
Extend Inquiry
Sample Data Table
Materials
Observations
Time for Water
to Stop Dripping
Sand
small grains, irregular shapes, whitish to brownish
9 minutes
Clay
tiny particles, regular shapes, tannish color
more than 15 minutes
Pebbles
large pieces, smooth shapes, various colors
2 minutes
More to Explore
Students could estimate the soil’s
permeability by observing after a rain to see
whether water is absorbed or pools on top of
the soil. Each group could test an actual
sample and compare results with data using
sand, pebbles, and clay.
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