Session 3: Water Cycle: Class 5 Abstract: This session on water cycle is for the students of class 5. The session is made interesting as the students with the assistance of the teacher will perform different experiments. This will give them a firsthand experience on the different stages of the water cycle. Objective: To demonstrate the concept of evaporation, condensation, transpiration and water cycle. Duration: 2 periods of 40 minutes each. Support Material For conducting experiments the following materials must be kept ready: For Step 1: (i) For experiment on evaporation: a kettle, burner, wet cloth, hanger to dry the wet cloth. (ii) For experiment on transpiration: a clear plastic bag, a string and a potted plant. (iii) For experiment on condensation: a container with water boiling on a stove, lid, a glass and very For Step 2: cold water or ice cubes. For experiment on water cycle: a large clear glass bowl, a small bowl, cling film and a weight (pebble). Steps Before explaining the concept of water cycle, the teacher should demonstrate a few experiments in class to teach the students the concepts of evaporation, transpiration and condensation. These processes play an important role in the water cycle. Step 1:- 40 minutes (a) Experiments on evaporation: The teacher may boil water in a kettle and show the students the steam emanating from the spout of the kettle and explain the concept of evaporation. He/ She may even wet a piece of cloth, hang it on a clothesline and ask the students to feel and check the wet cloth till it dries up. This should explain the concept of evaporation. Heat changes water into water vapor by the process of evaporation. In nature, the sun heats up water, found in rivers, lakes or the ocean and turns it into vapor or steam. The water vapor or steam being light rises up and leaves the river, lake or ocean and moves into the surrounding air.
(b) Experiment on transpiration: To conduct the experiment on transpiration, you will need a clear plastic bag (without holes) and a piece of string. Tie a clean, clear plastic bag around some leaves of the potted plant with a string (as shown in the figure below). Make sure not to damage the plant. Transpiration is a process by which plants loose water out of their leaves. This water adds to the water vapor in the atmosphere. It will be observed that, water droplets have collected inside the bag. These drops of water have actually come from the leaves by the process of transpiration. Check the bag daily to see what happens. (C) Experiment on condensation: Inverse process of evaporation is called condensation.
Hold your hand high over a vessel of boiling water, or place a dry lid above the rising steam. Your hands will feel wet and there will be droplets of water on the dry lid. The steam coming out of the boiling water condenses on your hand / lid. Secondly, if you pour very cold water or ice cubes into a glass on a hot day, you will find droplets of water on the outside of the glass. The water has not leaked through the glass! It actually came from the air. When water vapor from the air touches the cold glass surface, it turns back into liquid by the process of condensation. Step 2: 20 minutes The teacher may now demonstrate the following experiment to the students to help them understand the concept of the water cycle. Water Cycle experiment: Step A: Take a large glass bowl and fill it with some water so that it covers the bottom of the bowl. Step B: Next, place a small bowl in the centre of the large bowl. Step C: Now cover the top of the large bowl with cling film. Make sure that there are no gaps and at the same time the cling film should not be pulled too tightly. Step D: Place a pebble in the centre of the cling film in such a way that the film sags in the middle. Step E: Place the bowl in direct sunlight and leave it for few hours.
(Note: the small bowl should be placed exactly below the Step F: Write down your observation. Observation: After few hours we will see drops of water on the roof of the cling film. As time passes, these drops will get bigger in size and will drip down and collect in the smaller bowl. This happens because as the sun heats up the water in the large bowl, it will evaporate into water vapor. Water vapor being light will rise up and as soon as it touches the cool surface of the cling film it will condense into drops of water. As the process of condensation continues, the drops of water will grow in size and will be unable to remain hanging because of its increased weight and hence will drip down. The pebble placed as a weight on the roof of the cling film, will provide a sloping surface and guide the water to drip down and collect in the smaller bowl.
Step 3 10 minutes The teacher will wrap up the session on water cycle by comparing the results of the experiment to what happens in nature. Comparison: In the case of the experiment on the water cycle, the drops of water on the cling film became big and heavy and started falling down. Similarly In nature, the water evaporated from the seas, oceans, rivers, lakes etc. or the water vapor released by transpiration, rises up, and on reaching the upper atmosphere, cools and condenses to form clouds. With more and more condensation the drops of water in the cloud grow in size and therefore become too heavy to float in the atmosphere, and come down as precipitation, either in the form of rain or snowfall. When water falls back to the earth as precipitation, it may collect in the oceans, lakes or rivers or it may even end up on land. When it ends up on land, it will soak into the earth and become part of the ground water. This water cycle is a continuous process. Step 4: 10 minutes To reinforce the concept of the water cycle, the teacher can show this animation: http://www.epa.gov/safewater/kids/flash/flash_watercycle.html
Assessment/ Recapitulation Duration: 40 minutes Procedure: Divide the class into groups (4 members in each group) Make the students sequence the flashcards given in the appendix. The children will read the text given in the flashcards and sequence the same.
Appendix-1 Flashcards sheet-1
Flashcards, sheet -2
Flashcards sheet -3
Flashcards sheet- 4
Flashcards sheet - 5
Teachers Resource (i) Water Cycle The Water Cycle, also known as the hydrologic cycle, is the continuous movement of water from the ocean to the atmosphere and again back to the ocean. It goes on and on in a cyclical order. The Sun is the main driving force for the water cycle. The heat from the sun evaporates water from the earth s surface (oceans, seas, rivers, streams etc.). Plants also loose water to the atmosphere by the process of transpiration. The water vapor being light rises up. On reaching the upper atmosphere, it cools and eventually condenses, to form clouds. With more and more condensation, the drops of water forming the clouds become bigger and therefore too heavy to float in the upper atmosphere.
Precipitation (rain, sleet, or snow) is triggered, and water returns to the land or sea (collection). Some of the rain water or snowmelt water soaks into the ground. This is called infiltration or seepage and the water is stored between rock or clay layers as ground water called aquifer. But most of the water flows downhill as runoff (above ground as streams/ rivers) or underground, eventually returns to the seas or ocean as slightly salty water. Reference Material Water Cycle http://www.enchantedlearning.com/subjects/astronomy/planets/earth/watercycle.shtml Experiment on transpiration: http://shoalwater.nsw.gov.au/education/transpiration.htm Water Cycle experiment: http://shoalwater.nsw.gov.au/education/watercycle_experiment.htm Animation on water Cycle: http://www.epa.gov/safewater/kids/flash/flash_watercycle.html For flashcards on water cycle: <http://www.drippytheraindrop.com/drippysworldtrialstories/tomountainsandback/pa ge1.htm> (Many adventures of Drippy the raindrop To the mountains and back, written and illustrated by Joel M. Kimball)