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Sink or Float?
BROWARD COUNTY ELEMENTARY SCIENCE BENCHMARK PLAN
Grade K—Quarter 4
Activity 38
SC.C.1.1.2
The student knows that there is a relationship between force and motion.
SC.C.2.1.1
The student knows that one way to change how something is moving is to give it a push or a
pull.
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SC.H.1.1.1
The student knows that in order to learn, it is important to observe the same things often
and compare them.
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SC.H.1.1.3
The student knows that in doing science, it is often helpful to work with a team and to share
findings with others.
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SC.H.1.1.4
The student knows that people use scientific processes including hypotheses, making
inferences, and recording and communicating data when exploring the natural world.
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ACTIVITY ASSESSMENT OPPORTUNITIES
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The following suggestions are intended to help identify major concepts covered in the activity
that may need extra reinforcement. The goal is to provide opportunities to assess student
progress without creating the need for a separate, formal assessment session (or activity) for
each of the 40 hands-on activities at your grade.
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1. Use any of the “Science Extension” activities in class, but ask students to draw pictures
labeled before and after as they do or think about the investigation. Then have them
describe and explain the differences between the before and after pictures.
2. Use the Activity Sheet(s) to assess student understanding of the major concepts in the
activity.
In addition to the above assessment suggestions, the questions in bold and tasks that
students perform throughout the activity provide opportunities to identify areas that may
require additional review before proceeding further with the activity.
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activity 38 Sink or Float?
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© Delta Education. Photocopying and distribution prohibited.
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Sink or Float?
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OBJECTIVES
In this activity, students observe how
various objects behave in water and then
predict whether other objects will sink or
float.
For the class
The students
þ
operationally define sink and float
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predict and observe whether objects float
or sink
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discover why an object is more likely to
float, or more likely to sink
tongue depressor
tub, plastic
washer, large
1
balloon
1
rock
1
marker, felt-tip*
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paper towels*
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1 pair scissors*
2
trays, foam
water, tap*
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DSR Investigating Water
SCHEDULE
About 40 minutes
*provided by the teacher
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PREPARATION
VOCABULARY
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float
sink
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1
Make a copy of Activity Sheet 38 for each
student.
2
Cut each foam tray into quarters.
3
Half-fill the tubs with water, and inflate
the balloon.
4
You will need a rock, one of the plastic
tubs half-filled with water, and an inflated
balloon for a class demonstration.
5
Each team of four will need a cork, a
pencil, a paper clip, a sponge, a plastic
spoon, a straw, a tongue depressor, a
rock, a magnifier, one quarter of a foam
tray, a plastic tub, and a washer.
MATERIALS
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For each student
1
For each
1
1
1
1
1
1
1
1
Activity Sheet 38
team of four
cork
magnifier
paper clip
pencil*
rock
sponge
spoon, plastic
straw, plastic
BACKGROUND INFORMATION
When an object is placed in water, it either
sinks or floats. Materials that are less dense
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than water float. Materials that are more
dense than water sink. (Density is a measure
of mass per unit volume.) For example, ice is
less dense than water—1 cubic centimeter of
ice weighs less than 1 cubic centimeter of
water. Thus, ice floats in water. This explains
why ice cubes float in a glass of water.
When an object is placed in water, the object
pushes away—or displaces—a certain
amount of water. At the same time, the water
pushes upward with a force equal to the
weight of water displaced. If the weight of the
displaced water is equal to the weight of the
object, the object will float. If the weight of
the displaced water is less than the weight of
the object, the object will sink.
Activity Sheet 38
Sink or Float?
1. Which objects do you think will float?
Which objects do you think will sink?
2. Draw a line from each object to show sink or float.
Draw a line to the surface of the water if it floated.
Draw a line to the bottom of the tub if it sank.
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Differently shaped objects displace different
amounts of water. Hence, the density of the
material an object is made of is not the only
factor that determines whether it will sink or
float.
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Guiding the Activity
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In this activity, students put a variety of
objects in water to see which ones will float
and which ones will sink. When they try to
make a floating object sink, they feel the
water pushing the object back to the surface.
As a result, they begin to understand that
water pushes against objects just as objects
push against water.
Point to the clear plastic container of water at
the front of the classroom. Hold up a rock and
ask, What will happen if I drop this rock
into the water?
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Additional Information
Accept all reasonable responses.
Place the rock in the water and ask, What
happened to the rock?
Students should say that it dropped or sank
to the bottom of the tank.
Show students an inflated balloon and ask,
What will happen when I drop the balloon
into the water?
Accept all reasonable responses.
Place the balloon on the water and ask, What
happened to the balloon?
Students should say that it stayed on top of
the water or it floated.
activity 38 Sink or Float?
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Guiding the Activity
Additional Information
Write sink and float on the board, saying the
words aloud as you write them. Tell students
that if something sinks, it drops to the
bottom of a container of water. If something
floats, it rests on the surface of the water.
Explain that whether an object sinks or floats
is related to another property of water that
they will investigate today.
As appropriate, read or review page 12 from
the Delta Science Reader Investigating
Water.
2
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© Delta Education. Photocopying and distribution prohibited.
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Distribute a cork, a paper clip, a pencil, a
plastic spoon, a straw, a tongue depressor, a
rock, a magnifier, a foam tray square, and a
washer to each team and a copy of Activity
Sheet 38 to each student. Give students a
few minutes to examine their objects. Then
tell students to predict which objects they
think will float and which they think will sink.
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Students should record their predictions on
their activity sheets by circling the objects
that they think will float, and drawing a line
under the objects they think will sink.
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Figure 38-1. Testing objects to see whether they sink or float.
When students have finished making their
predictions, distribute a tub of water and a
sponge to each team. Tell students to test
each object to see whether it sinks or floats.
(See Figure 38-1 for setup.)
Remind students to wipe up spills with their
sponges as they occur.
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Guiding the Activity
Additional Information
Have students record their results on their
activity sheets by drawing a line from the
picture of each object to the surface of the
water, if the object floated, or to the bottom
of the tub, if the object sank.
4
After students have finished testing their
objects, hold a class discussion. Ask, Which
objects floated?
Students should say that the following
objects floated: cork, the pencil, the plastic
spoon, the straw, the tongue depressor, and
the foam tray square.
Students should say the paper clip, the rock,
the magnifier, and the washer sank.
Ask, What makes an object sink? What
makes an object float?
Students will probably say that heavy
objects sink and light objects float.
Tell students to push down on the cork
floating on the water and then let go. Ask,
What happens to the cork?
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Guide students to understand that the water
pushes against the cork as hard as the cork
pushes against the water, so the cork floats.
However, objects like the rock push against
the water harder than the water pushes
against them, so the rock sinks.
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Figure 38-3. In trying to sink a cork, students can
feel the water pushing back against the cork.
activity 38 Sink or Float?
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The students should say that the cork pops
back up to the surface (see Figures 38-2–38-4).
Explain to students that although they can
push the cork below the water’s surface, as
soon as they stop pushing, the water pushes
the cork back to the surface.
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Ask, Which objects sank?
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Figure 38-2. A cork floating in water.
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Figure 38-4. When released, a cork will immediately
return to the surface of the water.
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Guiding the Activity
5
Draw students’ attention to the Properties of
Water chart. Ask them what new property of
water they can add to the list.
Additional Information
Students should be able to say that water
pushes against objects placed in it.
Write pushes against objects placed in it on
the chart, saying the phrase aloud as you
write it.
REINFORCEMENT
CLEANUP
Set up an activity area with a tub of water
and a variety of objects. Let students predict
which of the objects will float and then test
their predictions.
Assessment Opportunity
This Reinforcement also may be used as
an ongoing assessment of students’
understanding of science concepts
and skills.
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Tell the students to pour the water in their
tubs into the sink. Then have students dry
the tubs and the objects with paper towels.
Return the tubs, corks, paper clips, plastic
spoons, magnifiers, rocks, straws, tongue
depressors, foam tray pieces, and washers
to the kit. Discard the balloon, and allow
the sponges to air dry.
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CIENCE AT HOME
SCIENCE JOURNALS
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© Delta Education. Photocopying and distribution prohibited.
Have students place their completed activity
sheets in their science journals.
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With their parents’ permission, have
students test some kitchen utensils and
items at home to see what sinks or floats.
Students might test a toothpick, a wooden
spoon, a metal spoon, a bottle cap, and
so on.
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Connections
needed to make the bottle sink? (The
bottle needs to be filled only partway.)
Tell each team to choose one “floater” and
one “sinker” from the objects they tested in
the basic activity or from among other objects
you provide. Then challenge students to
devise a way to make a “floater” sink and to
make a “sinker” float. Provide weights,
balloons, corks, pieces of foam, and other
materials for students to use in their
investigations. Give each team an opportunity
to tell the rest of the class about the methods
they tried and their results.
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Students may have had some difficulty
feeling the upward push of the water when
they pushed the cork down. Have them
repeat that part of the activity using a
tennis ball and then an inflated balloon.
What do they feel? (The water pushes back
even harder.) What happens when they let
go? (The ball and balloon pop up farther
than the cork.)
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• Float several hollow containers in the
water, such as a plastic cup, an empty
aluminum soft-drink can, a plastic bowl,
and a plastic soda bottle. Figure out a way
to make the containers sink. (Pour water
into them, or push them under the water to
fill them.)
• Half-fill a plastic bottle with water, screw
on the cap, and put it into the water. Does
it float? (yes) How much water has to be
put into the bottle to make it sink? (It has
to be filled to the top.) Try putting sand
into an identical bottle. How much sand is
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activity 38 Sink or Float?
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Bring in two or three child-size life vests used
by boaters. Let students try the vests on and
examine them closely to see how they are
made. Emphasize that everyone, even strong
swimmers, should wear a life vest when
boating or water skiing, and discuss the
reasons for this safety precaution. (Someone
who falls into the water in a boating accident
might be injured and unable to swim, or the
water conditions might be too rough for even
a strong swimmer.)
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Set up a learning center with a water table,
a wading pool, or other large container of
water, and let students take turns trying
the following investigations. In small
groups, discuss students’ observations
and ask them to offer explanations of what
happened.
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Invite a boating instructor (perhaps someone
who teaches at a children’s summer camp) to
visit the class and talk about his or her work.
Ask the visitor to describe the types of boats
he or she uses, how they are propelled and
steered, and safety precautions regarding not
overloading the boat and balancing the load.
Science and Health
Science Extension
þ
Science and Careers
Science, Technology, and Society
Give each team a fist-sized lump of clay or a
sheet of aluminum foil, and provide access to
a supply of identical metal washers.
Challenge students to see which team can
make a boat that will hold the greatest
number of washers without sinking or
tipping. After students have tested various
designs and chosen the most successful one,
let each team report its results and describe
its boat design to the other teams.
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Science Challenge