Term 2 Chapter 2 | 4th Science - Water | 4th Science : Term 2 Unit 2 : Water
Chapter: 4th Science : Term 2 Unit 2 : Water
Water
After learning this lesson, students will be able to • understand the change of states in water • describe the water cycle • explain the importance of water cycle • summarise rainwater harvesting and its uses
Unit 2
Water
Learning Objectives
After learning this lesson, students will be able to
- understand the change of states in water
- describe the water cycle
- explain the importance of water cycle
- summarise rainwater harvesting and its uses
Introduction
Water is the most abundant and precious resource on the Earth. It is found in oceans, seas, rivers, streams, lakes, ponds and even under the ground. All living things need water to live and to do many other activities. We have already learnt about this in the previous classes. Let us learn more about water in this lesson.
I. Change of States in Water
Let us do
See the given pictures and write down the state of each objects. (Solid, Liquid, Gas )
Water occurs naturally in three forms: ice, water and water vapour.
These forms are also called states of water. Ice is in solid form, water is in liquid form and watervapour is in gaseous form.
These states occur naturally because of temperature changes. Water becomes ice in cold regions, remains as water in oceans/rivers and becomes water vapour due to the heat of the Sun.
Let us do
Fill in the boxes given below with correct answers.
(Liquid, Solid, Melting, Freezing, Cooling, Heating, Gas)
Change of States in water
SOLID STATE (Ice)
Ice is a solid form of water. At temperature below 0° C water becomes ice. This process is called freezing.
LIQUID STATE (Water)
Water in liquid state is available in water bodies such as oceans, river, waterfalls etc.
GASEOUS STATE (Water vapour)
Water becomes water vapour as the temperature increases due to heat. Heating forms a white mist of extremely small water droplets in the air known as water vapour.
Try to Answer
1. Why water is a good example for all states of matter?
Because it is the only natural substance that can exist in all three states of matter at the temperatures normally found on Earth.
2. Which of the following is in liquid state? Rain/Ice/Snow
Rain
Let us do
• Fill water in an ice tray and keep it in the freezer. After few hours, take it out. What happened to the water?
The water changed from liquid state to solid state. It became ice.
• Now keep this ice tray on a table for some time. What happens to the ice?
Ice cubes melt and turn into water. Now water changes from solid state to liquid state.
• Pour water from the ice tray into a kettle. Ask an elder at your home to heat the kettle and observe the mouth of the kettle when the water starts boiling. What do you see?
We see white smoke (water vapour) coming out from the mouth of the kettle. Water changes from liquid state to gaseous state. It became steam.
II. Water Cycle
In nature, water keeps changing its state. Let us see how this happens. Due to the Sun‛s heat, water in oceans and rivers changes into water vapour and rises up.
Water becoming water vapour on heating is called evaporation. The water vapour, when comes into contact with cool air, becomes water droplets. This is called condensation. The water droplets combine to form clouds. The water droplets continue to combine, and they become big and heavy. These water droplets then fall down as rain. This is called precipitation. In colder places, combined water droplets come down as snow, sleet or hail. This continuous change of water from one state to another in nature is called water cycle.
The continuous cycle through which water is circulated by different processes like evaporation, condensation and precipitation is called water cycle.
Water Cycle
Each day, we lose a little more than a cup of water when we exhale.
Think and answer
What happens to the water in a wet cloth?
The water in a wet cloth gets evaporated. Hence the cloth gets dried up.
Try to Answer
Choose the correct answer.
In the water cycle ________
2. only condensation is involved
3. evaporation and condensation are involved
Answer: (c) evaporation and condensation are involved
Importance of water cycle
- To improve the availability of ground water.
- To control the Earth‛s temperature.
- To provide water to plants and animals especially humans.
- To recycle the Earth‛s supply of water constantly.
Try to Answer
1. Unscramble the words and fill in the blanks.
ondencsaonti, vaeionorpat, ecippitatrino
condensation, evaporation, precipitation
2. Is water cycle important for farming?
Yes
3. Why is water cycle important to human?
To improve the availability of ground water.
4. Name the process which is responsible for the formation of droplets on the surface of a glass of cold drink.
condensation
73% of our brain‛s mass consists of water. The Antartic region has about 70% of the worlds fresh water.
III. Rain Water Harvesting
‘Rainwater harvesting’ is the process of collecting and storing rainwater for future use. Rainwater can be collected in natural reservoirs or artificial tanks. Roof top harvesting is also a type of rainwater harvesting. The rainwater on the top of the building is collected and passed into the ground through pipes. Water passing through the pipes enters the pit which consist of gravels and Coarse sand. As it passes impurities are filtered and stored as ground water.
$$ H_2O $$ is the chemical formula of water.
1 inch of rainfall on a 2,000 sq.ft. roof is equal to 4,800 litres of water.
Benefits of rainwater harvesting
- It increases the ground water level
- It can be used for agriculture
- It increases the availability of water for living things
Rain water harvesting is the only way to conserve rain water
- The rain water harvesting was launched in the year 2001 by the Tamil Nadu government.
- Tamil Nadu is the first Indian state which made rainwater harvesting as mandatory.
Try to Answer
1. List out some other benefits of rain water harvesting.
2. Suggest some ideas to save rainwater in your school.
Let us do
Tips to construct a rainwater harvesting pit at school/home.
Construct a pit of any shape or size. It may be generally constructed, 1-2 metre wide and 2-3 metre depth. The pits can be filled with boulders, gravels and Coarse sand.
Put the boulders in the bottom, sand in the top and gravels in the middle.
Let us do
Discuss with your friends.
Rain water harvesting has an important role to protect our environment.
It increases the ground water level. It reduces flooding and soil erosion and reduces water scarcity.