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Grades K-3


Prior to this lesson the students should have experience with bar graphs, balance scales, and some basic understanding of the properties of liquids.

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.
ITV Series
Science for You: Bubbles, How Do Insects Walk on Water? (Agency for Instructional Technology)

Learning Objectives
Students will be able to:

Pre-Viewing Activities
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.

Focus Viewing
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.

Viewing Activities
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.

Post-Viewing Activities
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 uncled@delphi.com which reaches "Mr. Wizard" (The Discovery Channel). "Newton's Apple," another Internet access, can be reached at newtons@maroon.tc.umn.edu. 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 these results.

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 represented.

Outdoor Activity:
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 new "blob."

Master Teacher: Barbara Passo

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