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IT'S CLEAN, IT'S FRESH AND ONLY THREE BILLION YEARS OLD - WATER!
Grades 7 - 9

Overview

This lesson is about the water cycle. Without the ability of water to vaporize, condense and fall back to Earth, life on this planet would not survive. This lesson explores, using some very entertaining video and fun, hands-on activities, the process behind each phase of the water cycle; evaporation, condensation, precipitation and collection. The Water Cycle Lesson will take two approximately 45-minutes class periods.
ITV Series
Bill Nye the Science Guy - "The Water Cycle"
Learning Objectives
Students will be able to:
Materials
Per student group or pair of students:
Vocabulary
Pre-Viewing Activities
Give each team of two students a small cup of water, a clean ice cube and a covered vial of damp air. Ask them to list as many observations about each substance they can see in three minutes.

Allow students to sip the water and lick the ice cube in order to make complete observations. Elicit responses from the students regarding the similarities and differences between the samples.
Focus Viewing

First Segment

To give students a specific focus for viewing, tell them to carefully watch and listen to the first short segment of the program and list one significant property of water that they may have omitted in their observations a few minutes before; one that is very clearly mentioned in the first segment (that the water in their cup is approximately 3.5 billion years old!)

Second Segment

Explain that condensation is the process where water vapor turns back into liquid water. This section of the video provides an excellent explanation of the process and will provide a nice lead-in to the next activity. To focus the students' attention, tell them to be prepared to answer this question about his segment:" How is condensation different from evaporation?"

Viewing Activities

First Segment

START tape just after musical introduction to program. PAUSE after the words "you could be drinking what was once dinosaur spit." Take a large swallow of water and restate the last phrase ("You could be drinking what was once dinosaur spit.") To check for comprehension, ask for other examples of the origin of the water in their cups. Prepare for a lively discussion!

To continue their focus, tell students to watch the next segment of the video and write down the term Bill Nye gives for the "Moving around of water."

RESUME from "water is just an amazing substance." PAUSE at the point where the terms "water cycle" and "hydrologic cycle" appear on screen in large white letters, immediately after "heh, heh, heh."

Ask students to list three other examples of cyclic patterns in their own environment. Briefly discuss a few of the examples taking care not to lose the impact of the fast pace of the video. Tell them to watch the next section of the video and to continue their focus, have them list four major parts of the water cycle.

RESUME PLAY. STOP after the phrase, "...it floats to the sea to start the cycle all over again!" To check for comprehension, ask the students for specific examples of evaporation, condensation, precipitation and collection. If possible, use examples from their own environment.

Hand out a labeled diagram of the water cycle apparatus shown in the program (attached). Discuss.

Explain that in this section of the lesson, students will explore the variables that affect evaporation, condensation and precipitation.

Evaporation:
Hand out Evaporation Investigations and materials listed on their investigation sheet (use one kit per student team). Have students complete the investigation with as little help from you as possible. It might be useful to point out the materials at their disposal. Allow students to design one procedure, carry out the procedure, collect data and report on their findings in writing. At the end of the investigation the students should complete the questions at the end of the investigation.

Upon conclusion of the investigation, discuss the results with the students. (Variables, such as temperature of the air, water circulation, surface area, etc. will affect the evaporation rate.)

In order to understand the concept of evaporation, it is important to be able to visualize the process on the molecular level. After a discussion of the factors affecting the rate of evaporation, encourage students to carefully watch and listen to the next segment pertaining to molecular motion. To give students a focus for viewing, ask them to pay particular attention to the demonstration using plastic beads as molecules.

FAST FORWARD to black and white screen entitled "Molecular Moments." PLAY and STOP at the conclusion of this segment. To check for comprehension, probe students for the molecular basis for evaporation of water based on the illustration of the "bead" molecules (Not all molecules are moving at the same speed).

Second Segment


START TAPE at "Who's the Scientist." PAUSE quickly after "See that! That uh..." To check for comprehension, ask students to provide the term in question (condensation).

RESUME PLAY. PAUSE after "...is where clouds come from." Check for comprehension by asking how a cloud might form in the classroom.

RESUME PLAY. PAUSE after "...water needs a place to stick for condensation to happen." Check for comprehension by asking students to explain how condensation is different from evaporation with respect to energy losses and gains.

In this investigation students will attempt to forma cloud by causing condensation to occur in a clear plastic 2-3 liter soda bottle (NOTE - This won't work until a key ingredient is added. This missing substance will be revealed int he next segment of the video.)

Hand out materials for "Cloud in A Bottle Investigation". Direct students to make a circle by bending the flexible thermometer and taping it together. Then have them put the thermometer in the bottle, recap it and record the temperature in the bottle. How, have them squeeze the bottle and describe what happens. The temperature should rise if they squeeze hard enough.) Next, unscrew the cap and add enough water to cover the bottom of the bottle, recap the bottle and squeeze again. While they are squeezing the bottle and heating it up, ask what would happen if they suddenly released pressure on the bottle (they should realize that the air in the bottle would cool). Cooling the air as the video clearly shows produces condensation and should form a cloud. Direct students to perform that task now!

You will see some disappointment on their faces when absolutely nothing happens.

Explain that in this next section of the video, Bill Nye attempts to perform the same experiment in much bigger bottle - with much the same results as the students will experience. To give students a specific focus for viewing, tell them they should discover why their attempt at cloud-making didn't work.

RESUME PLAY at "It's just the water vapor in the nearby air condensed." PAUSE after "...three, two one..." To check for comprehension, ask students to relate this to their own attempt to make a cloud.

RESUME PLAY from above. PAUSE after "We'll need the dust from these two matches!" At this point allow the students to add smoke to their bottles. Mention that dust is just a simple term used to describe all kinds of particles to which water molecules can cling. The technical term for this "dust" is condensation nuclei.

RESUME PLAY. STOP after cloud formation and explanation"..it's science!" To check for comprehension, ask the students to write a recipe for a cloud. They should be able to list ingredients, materials, procedure, etc. just like in a cookbook.

Preview the process of evaporation and condensation. Explain, however, that unless the condensed water falls back to Earth, there would be no cycle and now water for life forms to use. In this next segment we will explore the process of precipitation.

Direct students to listen for an explanation of how water in the clouds can return to Earth.

START after "way cool science". PAUSE after "This is rain! Isn't it great?!" To check for comprehension PAUSE and ask students to restate the process that produces precipitation. (Water molecules need to cling to one another to become large enough to fall.)

RESUME and PAUSE after terms , RAIN, SLEET, HAIL AND SNOW appear on the screen. Check for understanding of terms by asking class to name the four common forms of precipitation. This is a good point to review the differences between sleet and hail, commonly confused forms of precipitation. (Sleet forms as rain freezes on the way down through cold air. Hail forms from a cyclic motion which produces multiple stages of freezing and thawing. This produces the concentric ring patterns often seen in a cross section of a large hailstone.)

RESUME PLAY and STOP after "...all the time it's evaporation. It's just another "-shun" word." To check for comprehension, ask the students for the meaning of collection as it pertains to the water cycle.

By way of introduction, tell students that in this final section of the program, the importance of reusing the limited water available on Earth is emphasized.

To give student a specific focus for viewing, tell them to carefully watch the next segment of the video to get a clear demonstration using a baseball to represent the Earth and a dropper to represent the amount of usable water on earth.

START after "old film clip" and PAUSE after the words "We must put an qual amount of water into our bodies each day or we'd perish...and that includes you, pal!"

To check for comprehension, asks students to recall the amount of water that is available to drink. You could also begin a discussion of water pollution and its effect on the limited fresh water available for humans at this point or bring this concept in as an extended topic after the lesson on the "Water Cycle."

In the next section of the Bill Nye program, the importance of the water cycle is, shall we say, STRESSED! HAVE THE STUDENTS WATCH THE SEGMENT PAYING CAREFUL ATTENTION FOR SEVERAL REASONS WHY THE WATER CYCLE IS SO IMPORTANT.

RESUME PLAY. STOP after "We'll be back in a moment with Bill Nye the Science Guy." To check for comprehension, have the students write a brief essay on the importance of the water cycle to life forms on earth. Discuss some of their interpretations as a class. Ask for things that people can do to protect the water cycle.

START after "Just Do It" logo. Conclude the lesson with the "Water Cycle Rap."

First Segment

This demonstration will reinforce the concepts shown in the video segment, "Molecular Motion." It is often difficult for students to conceptualize molecules (matter) not only contain mass but take up space as well. In this demonstration you will show that evaporation occurs when droplets of water are placed in a dry, sealed bottle. See Materials List for Evaporation experiment and diagram attached.

Vapor pressure is that part of air pressure that is caused by water vapor in the air As water evaporates, the number of molecules of water for a certain volume of space increases. This in turn creates a greater pressure. With a tube containing food coloring it is possible to approximate the evaporation of water through the changes in the height of the fluid indicator. Set up the apparatus as shown int he diagram. Make sure the indicator fluid is at a measurable point on the meter stick. With a dropper partially filed with water, carefully, without squeezing any water down into the bottle, place the dropper in the hole in the stopper of the bottle so that there is a seal.

Discuss the fact that since there is now water to evaporate in the bottom of the bottle the air pressure in the bottle is constant. (A change in temperature would change the pressure inside the bottle.)

Gently squeeze a few drops into the bottle and ask the class to describe what happens. As they watch the indicator fluid rise in the long glass tube, ask the students if the rate of change of the fluid in the tube is constant. (The indicator rises quickly at first and then slows down. It will reach a certain level depending on the temperature of the room. This level is called the saturation vapor pressure which means that the air in the bottle can't evaporate any additional moisture without condensing an equivalent amount.) In this investigation, the added molecules of evaporating water take up space int he bottle, which in turn caused pressure inside. The easiest way to release the pressure is by pushing the indicator fluid forward, up the tube. The instrument that has just been observed is called a Manometer.

In the previous section we focused on the process of evaporation. In this section we will reverse the process and explore how water vapor condenses. If this part of the lesson is to be completed on another day, a review of the previous lesson on evaporation would be recommended.

Second Segment

Use the "manometer" to see how temperature affects the amount of evaporation by using bottles with differing air temperatures. Graph the rise in the indicator fluid for each of three different temperatures. Have students display and explain their results.

Make a poster-sized diagram of the water cycle labeling each of the four major parts.

Set up the "Cloud in a Bottle" and start with polluted water instead of clean water. Try different forms of polluted water like salty, soapy, muddy, etc. and see what happens. Describe results.
Extensions
WEATHER STUDIES:
Have your Earth Science teacher help you find the Dew Point and Relative Humidity of the air. Keep a record of the changes that take place for one month. Compare this to any weather changes that occur.

LANGUAGE ARTS:
Write a fictional short stry on the life history of a water molecule.

Master Teacher: Gib Brown
Mountain Lake Public Broadcasting/Plattsburgh, NY


NOTE TO TEACHER

This lesson will focus on the relationship between the different phases of water and the importance of each phase in the completion of the water cycle. "Bill Nye, the Science Guy: The Water Cycle" allows you to interject several hand-on activities that will allow students to explore the relationships between the different phases of water and the importance of the recycling of water on life forms on earth.
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