Prior to this lesson the students should have experience with
bar graphs, balance scales, and some basic understanding of the properties
This lesson and its extensions will provide students with an understanding
of surface tension caused by the cohesion of water molecules. The students
will estimate and graph the number of drops of water that can be placed
in an already filled glass. The teacher will demonstrate the principal of
surface tension by having two identical glasses, each filled with water,
balance with one inverted on top of the other (the open ends of each will
be touching) without any water spilling out. The teacher will place a nickel
in between these two glasses while the students observe that water will
not pour out. (Both of these experiments are shown in the video). The students
will measure the amount of surface tension using a balance scale and some
small weights. They will diagram the appearance of several liquids and label
them. This lesson might require more than one class period.
Science for You: Bubbles, How Do Insects Walk on Water? (Agency
for Instructional Technology)
Students will be able to:
- demonstrate the cohesion quality of water by estimating, graphing
and adding water to an already filled glass of water;
- analyze, distinguish and identify the different cohesion qualities
of four different liquids;
- demonstrate the force of surface tension by measuring the amount of
surface tension on water using a balance scale and small weights.
- for graphing: "post-it" note pads
- a large graph for the students to place their post-it notes
- crayon, one per student
- activity sheet
- paper cups
- paper towels
- two identical glasses
- one nickel
- a basin of water large enough to submerge the two identical glasses
- four liquids such as vinegar, water, oil and dish detergent
- pencils, one per student
- eye droppers, one per student and teacher
- magnifying glasses, one per student and teacher
- waxed paper
- balance scales, one end should have a piece of thread attached to
a piece of 2" X 2" flat of plastic suspended from it; the other
end should have an empty paper cone cup suspended from three pieces of thread;
one per group of 3-4 students (see worksheet)
- containers for water with openings larger than the square of plastic
- tiny weights such as toothpicks or tiny nails
- surface tension - this term will be the focus of the lesson and will
be defined in the video as the "skin" which forms on the surface
of a liquid. It does not need to be introduced before the video. (For the
grades and ages this lesson is intended, the above definition, as stated
in the video, is adequate. A more scientific definition is that surface
tension is caused by the force per unit of area on the surface of the liquid
due to the cohesion of the liquid.)
The room should be set up with groups of 2-3 students sitting
at flat-topped surfaces. Each student should have a post-it note attached
to his/her space and a crayon.
A large bar graph made with mural paper with space large enough to hold
the post-it notes should be placed within reach and vision of the students.
There should be two glasses of water within the vision of the students.
One glass should be filled with water into which a few drops of food coloring
have been added. This will enable the students to better observe the liquid
inside the glass.
The teacher should have a basin filled with water large enough to submerge
the two identical glasses and some paper towels.
If possible, have pictures of water and its uses, books relating to water,
and centers set up for water activities around the room.
The materials for the post-viewing activities should be prepared for each
group. These should include a pencil, a worksheet, a piece of waxed paper,
eye droppers, magnifying glasses and containers of four different liquids.
The containers of liquids should be labeled for identification.
The teacher will initiate a discussion of the properties of liquids which
will include the fact that liquids take the shape of their containers.
The focus for viewing is a specific responsibility or task students
are responsible for during or after watching the video to focus and engage
students' viewing attention. Tell the students they are about to learn truly
amazing facts about liquids. One amazing fact is that liquids like to stick
to themselves much the same as the post-it note is sticking to their desks.
Tell the students that they will be estimating how many drops of water,
if any, can be added to a glass already filled with water.
BEGIN the video with the screen of a boy holding an eye
dropper. There are two glasses of water in front of him and the picture
is inside a frame.
STOP the video when the two boys have stated, "I'm trying to
see how much this can hold of water without it overflowing. It's practically
about to overflow." Place a glass of water on a demonstration table.
Tell the students they are going to estimate how many drops of water, if
any, can be added to the glass already filled with water. Using the crayon,
have them write their estimate and put their initials on the post-it note.
Have them place their post-it note in the appropriate place in the range
of estimates on the bar graph. Have two students come to the front of the
room. Tell one that it is his/her responsibility to observe the glass from
the side in order to report what happens to the shape of the water as additional
water is added to the glass. Demonstrate to the second student how to carefully
add drops of water to the glass. (Water should be added using an eye dropper
and dropped carefully from the side of the glass.) As the student carefully
adds the drops of water to the glass, the teacher and the rest of the students
should count them out loud. When the water spills over, ask them to tell
why they think so much water could be added. Have the student who was observing
the shape of the water in the glass describe what he/she observed. (This
student should have been able to see a convex shape - outward curving -
form at the top of the glass.) Many students will not know the term "convex"
and the teacher should tell them and write it on chart paper. Refer to the
graph. Discuss their estimates. Tell them liquids have surface tension which
makes them want to stick to themselves and that when the video resumes they
will learn about surface tension.
RESUME the video and PAUSE when the screen has the picture
of water molecules and the word "surface" appearing in the middle
and the audio has stated, "Surface molecules are pulled together a
little more tightly." Use this screen to point out to the students
how the molecules in the glass are moving freely about while the molecules
at the top of the screen appear to be forming a boundary. This "boundary"
is the surface tension or the water wanting to stick to itself.
Re-focus the students' attention. Tell the students they will observe an
inverted glass of water balanced on top of another glass of water while
little, if any, water spills out. Tell them that a nickel can even be placed
in-between the two glasses! Tell them to think about the reason for this.
RESUME the video and STOP after the demonstration of the two
glasses filled with water with a nickel in-between them is completed. The
teacher should perform this demonstration for the students and tell them
that surface tension is preventing the water from spilling out. Tell the
students they can do it at home using a sink.
FAST FORWARD and BEGIN at, "All liquids have surface
tension, but some have more than others." This occurs just after the
screen with the water coming out of the bottom of a tin can. Say, "It
will be your responsibility to describe surface tension and to compare the
amount of surface tension of different liquids." RESUME the
video and PAUSE after, "The ones that bead up like water have
more surface tension and the flatter ones have less." The screen will
have pictures of labeled oil, soap and water. Point out the different convex
shapes of the three liquids. Have the students tell which liquids have more
surface tension. STOP the video.
Tell the students to remember what they have just seen and that
they will be given four liquids to test for surface tension. Tell them they
will have the task of analyzing four liquids and comparing them to each
other in order to determine which liquid they think has the greatest surface
tension and which the least and to arrange them in order. They will have
to draw, label each liquid, and write the reasons for placing them in the
order in which they did. (Younger students may not be able to write their
evaluation of the liquids. They should be told to order them by illustration.)
Review through discussion what surface tension is and how to tell if a liquid
has a greater or lesser amount of "convex" and what it means.
Pass out the waxed paper, eye droppers, pencils, magnifying glasses, four
different liquids and worksheet #1. Students should begin the activity.
Give the students about fifteen minutes to complete the worksheets. Evaluate
their observations through discussion. Collect the worksheets and gather
all the materials.
Post-Viewing Activity #2
Give each group a balance scale as described in the materials list. Tell
them they are about to measure the tension of the surface of water. That
is, how much force is required to lift the plastic square from the surface
of the water. Pass out worksheet #2. Use small weights such as toothpicks,
tiny nails or even bits of paper to balance the weight of the plastic against
the paper cup. Put these into the cup. Place a container of water under
the plastic square so that the undersurface of the plastic is touching but
not under the surface of the water. Add weight to the paper cup to determine
how much tension the surface of water has.
Technology: There are several Internet addresses that
both teachers and students can access. One is firstname.lastname@example.org which reaches
"Mr. Wizard" (The Discovery Channel). "Newton's Apple,"
another Internet access, can be reached at email@example.com. There
are several water experiments there that can be done in and out of the classroom
as well as listings of other science topics.
Social Studies/Geography: The students can make a pile of dirt or
sand on the playground and pour water over it to see how the water falls
once it hits the dirt. This is a good introduction to the formation of rivers
and other bodies of land or water. This activity also demonstrates the cohesion
quality of liquid.
Science: Where Does It Go?
Refer to the activity above. To extend this activity the students should
be given tongue depressors. Have them color the tongue depressors as follows:
measure two inches from one end and draw a line in one color. Continue measuring
from that point in one-inch increments and draw lines. Have the students
place the tongue depressors into the dirt pile two inches deep. Pour the
water over the pile. Observe what happens to the tongue depressors. Have
the students measure the distance the tongue depressors traveled to see
what happens in storms as the result of erosion and to see the direction
in which the depressors traveled. This activity shows the erosion of soil
and the displacement of it.
Ponds, Insects and Surface Tension
Through inductive reasoning the students can determine the approximate weight
of an insect that can walk on water. Take a trip to a pond or other body
of water to which insects will be attracted. Discuss with the students why
they think some insects can walk on water. Lead them to realize that the
weight of an insect is not enough to break the surface tension. Have the
students answer the question, "How much or little does an insect have
to weigh before sinking into water?" If possible, find some insects
that are dead. Have the students observe the feet of these insects using
magnifying glasses. Tell the students to explain what adaptations have been
made enabling these insects to walk on water.
Wash It Away
Once the students have an understanding of surface tension, activities demonstrating
how to break surface tension can be done. Soap is an easily obtained material
with which to accomplish this. Have the students place several drops of
water onto waxed paper. Add a drop of soap. Watch what happens.
Sink or Float
Fill a basin with water and have the students place several objects into
the basin that will float. Have them describe why they think they float
rather than sink. An inquiry of them might be, "How do boats float?"
Have them compare the surface tension of the floating objects with the plastic
square using the method described in the action plan.
How Much is Too Much
Use the green vegetable trays that have holes in them for this experiment.
Have the students guess whether or not these will sink or float when placed
into a basin of water. Record their responses. Try it. After trying it,
place weights in the trays to see how much weight can be held without causing
the trays to sink.
Language Arts: For younger students have a large picture of a drop
of water placed on chart paper. Brainstorm with the students about the various
ways they use water and list these on the chart paper. For older students
have the students list the various ways in which they use water and research
the approximate amount of water used each day in their households. Graph
Math: Have the students estimate and graph the number of drops of
water that will stay on a penny. Do the measurements. Find the difference
between the estimate and the actual amount of water. (Penny Fill worksheet).
Art: Give the students watercolor paints and water. Tell them to
paint a picture that has something to do with water. The students should
share these pictures and the teacher can make a class list of the activities
Water Scavenger Hunt
Give the students a list of items to find outside that show either the presence
or absence of water. Some items on the list might be: a plant that is full
of water, soil that is damp enough to stick together when squeezed, a place
where the ground is so hard that water will not soak into it, a place where
a puddle has evaporated, a place where water is evaporating, a place where
birds take a bath in dust rather than in water, a place where something
is floating or resting on water.
This is a cooperative tag game intended to show the cohesive quality of
water. The area in which the game is played needs to have the boundaries
clearly defined. One person is selected to be the "blob" which
is a molecule of water. Any person touched by the "blob" becomes
part of the "blob" by linking elbows. The "blob" continues
to grow as would drops of water when it finds other drops of water. The
"blob" can only tag people if it is in one piece. If the "blob"
breaks it must go to a designated area. When four more people are in that
area they may form a "blob" and attract (tag) other free players.
If the players have trouble staying together, the teacher can split the
group into two or more "blobs." The last person left becomes the
Master Teacher: Barbara Passo
Lesson Plan Database
Thirteen Ed Online