Water Olympics

Contributed by: Tami Caraballo from Project Wet

OVERVIEW

Purpose:

The purpose of this lesson is for students to become familiar with the properties of water, adhesion and cohesion,through hands-on learning activities.

Essential Question:

How do the unique water properties of adhesion and cohesion impact the importance of water to living things?

Key Vocabulary:

Hydrogen bonds

Cohesion

Adhesion

Polarity

Surface tension

Capillary Action

Materials:

Materials are listed on each activity card

A Drop of Water by Walter Wick is a beautiful book to share with your students

Prep Time:

30 minutes to read through lesson plan make copies of the data table for each student andprepare for the station activities.

Class Time: About 50 - 60 minutes.

Background:

Note: This background information is for the teacher’s use. Do not give this information to students before they have a chance to explore the properties of water. You many chose to give this information following the activities but not before.

The nature of the water molecule causes it to be attracted to other water molecules as well as to molecules of other substances. Without these qualities, plants could not get water, and blood would have difficulty traveling throughout the body. The attraction between water molecules is called cohesion. The attraction of water molecules to other materials, like glass or soil, is called adhesion.

Simply looking at its surface can see evidence of water’s attraction to itself. If a glass is filled to the brim and more water is added gently, the level of the water will exceed the top of the glass. The cohesive force between water molecules causes the water surface to behave as though a thinly stretched membrane that is always trying to contract covers it. This phenomenon is called surface tension. In many ways, surface tension is like water’s skin.

Water’s surface is so strong it can even support paper clips and needles. Surface tension is important to the survival of many aquatic organisms, including insects. The water strider lives on the surface of fresh water. Compared to a piece of wood floating in the water, paper clips and water striders are not actually floating. Instead, they are held up by bonds between water molecules (see “Hanging’ Together”). Floating objects do break the surface tension of water. They stay afloat because water molecules deeper in the water can support the weight of the objects

Soap also breaks surface tension. For example, when a small piece of cardboard cut into the shape of a boat is placed on water, it will stay in one place. This is because water is equally attired to all sides of the cardboard. When soap is placed at the back end of the cardboard boat, water molecules are still pulling at the front end of the boat, but not the back end. (The soap reduces the pull of water molecules on the back end of the boat.) This causes the boat to move forward. (An analogy would be a tug of war. The rope is the boat ad the people pulling on each side are the water molecules. If several people on one end let go [representing the addition of soap] the roper [boat] would be pulled toward the opposite end.)

The same forces that cause water to be attracted to itself cause it to adhere to other substances. If this didn’t happen, water would slide off everything like water off a duck’s back. Whatever appears to defy gravity as it moves up a paper towel, through spaces among soaked particles, or along a piece of yarn at an angle to the ground. This is called capillary action and results from water molecules being attracted to molecules of the towel (or soils or yarn) and to each other. However, the molecules can only travel so far before the force of gravity overcomes the attraction of water to itself and to other molecules.

LESSON PLAN

Learning Objectives

  • Students will demonstrate adhesive and cohesive properties of water and relate adhesion and cohesion to daily activities.

Preparation

  • Divide the classroom into stations; an Olympic event will take place in each area.
  • Place an Olympic event at each station and set up the materials at that event. Make sure you have enough for 10 teams to participate at this event.

Classroom Activities

  1. Divide the students into small teams of no more than 3 students per team. The teams can give themselves names such as “The Indian Ocean”.
  2. Give students a copy of the H2Olympics Scoreboard to tape into their science journal (this table is found on a separate document). They should carry their science journal with them to each station and record their observations.
  3. Tell students they will be participating in a Water Olympics to demonstrate some amazing feats of water.
  4. Teams of students will start at separate events and may not move until the teacher rings the bell to end that event. The teacher should time the event.Have students find their event and circle this event to begin their record keeping.
  5. Model for the students what the events will be like and how to complete the table by conducting the following demonstration. Be sure to practice the demonstration before performing in front of students. :
  6. Show students a beaker partially filled with colored water (put one drop of food coloring in water in a beaker of 250 ml or more). Tell them you are going to make water defy gravity as it “walks a tightrope” from the beaker to the container.
  7. Hold the beaker, the floss string and the empty container as shown in the illustration.
  8. Slowly pour the water down the string.
  9. In your data table in the column called Demo, complete the rows in that column.
  10. You may want to do this with your students
  1. Once all teams have visited all stations, have students compare the results of different events.

Assessment:

  • Student should list 3 properties of water and indicate the evidence from this lab that illustrates that water property.

Extension (optional if time permits):

Students can investigate how soil absorbs water to explore adhesion and cohesion further. Challenge student to concoct a soil that will absorb the most water. Have students collect soil samples and remove excess water by leaving the sample spread out in the sun for about six hours. Instruct them to describe their soilrecipeand why they thin it will absorb water well. After the samples are dried, provide studentswith eh following instructions:

  • Use a cup with tiny holes punched in the bottom. Record the weight of the cup: ___. Fill the cup with your soil; pack t tightly. Record the weight of the cup and the soil, and subtract the weight of the cup. How much does the dry soil weight? ___. Place the cup in a pan filled with a shallow layer of water. After 30 minutes, remove the sup form the water and carefully wiper excess water from the sides and bottom. Weight the cup and soil and subtract the weight of the cup and dry soil. How much water dis your soils absorb? ____

Compare the surface tension of other liquids. Using a minifying glass investigate drops of water, hydrogenperoxide, and alcohol. How do they differ? Can a paper clip be supported on the surface of each of these liquids?

Resources:

Hurd, Dean, et al. 1988. Prentice Hall Physical Science. Engelwood Cliffs, N.J.: Prentice Hall, Inc

Lamb, William G., et al. 1989. HBJ Physical Science. Orlando, Fla.: Harcourt brace Jovanovich, Inc.

Watson, Philip. 1982. Liquid Magic. New York, N.Y.: Lothrop, Lee & Shepard Books.

Wick, Walter A Drop of Water