Page 1 136 SCIENCE 14 Water S uppose for some reason your family gets only one bucket of water everyday for a week. Imagine what would happen? Would you be able to cook, clean utensils, wash clothes or bathe? What are the other activities you would not be able to do? What would happen if we do not have easy access to water for a long period of time? Apart from drinking, there are so many activities for which we use water (Fig. 14.1). Do you have an idea about the quantity of water we use in a single day? each activity by you and other family members. You may use a mug, a glass, a bucket or any other container to measure the amount of water used. Fig. 14.1 Uses of water 14.1 HOW MUCH WATER DO WE USE? Activity 1 List all the activities for which you use water in a day. Some activities are listed in Table 14.1. Make a similar table in your notebook. Throughout the day, measure the amount of water used for Table 14.1 Estimation of the amount of water used by your family in a day y t i v i t c A f o t n u o m A d e s u r e t a w g n i k n i r D g n i h s u r B g n i h t a B s l i s n e t u g n i h s a W s e h t o l c g n i h s a W s t e l i o T r o o l f g n i n a e l C r e h t o y n A n i d e s u r e t a w l a t o T y l i m a f a y b y a d a You now have a rough idea as to how much water your family uses in a day. Can you estimate the amount of water used by you for personal cleanliness in a day. Using this information, calculate the amount of water needed by your family in a year. Now, divide this amount by the number of members of your family. This will give an idea of the amount of water needed by one member of your family in a year. Find the number of people that live in your village or town. 2020-21 Page 2 136 SCIENCE 14 Water S uppose for some reason your family gets only one bucket of water everyday for a week. Imagine what would happen? Would you be able to cook, clean utensils, wash clothes or bathe? What are the other activities you would not be able to do? What would happen if we do not have easy access to water for a long period of time? Apart from drinking, there are so many activities for which we use water (Fig. 14.1). Do you have an idea about the quantity of water we use in a single day? each activity by you and other family members. You may use a mug, a glass, a bucket or any other container to measure the amount of water used. Fig. 14.1 Uses of water 14.1 HOW MUCH WATER DO WE USE? Activity 1 List all the activities for which you use water in a day. Some activities are listed in Table 14.1. Make a similar table in your notebook. Throughout the day, measure the amount of water used for Table 14.1 Estimation of the amount of water used by your family in a day y t i v i t c A f o t n u o m A d e s u r e t a w g n i k n i r D g n i h s u r B g n i h t a B s l i s n e t u g n i h s a W s e h t o l c g n i h s a W s t e l i o T r o o l f g n i n a e l C r e h t o y n A n i d e s u r e t a w l a t o T y l i m a f a y b y a d a You now have a rough idea as to how much water your family uses in a day. Can you estimate the amount of water used by you for personal cleanliness in a day. Using this information, calculate the amount of water needed by your family in a year. Now, divide this amount by the number of members of your family. This will give an idea of the amount of water needed by one member of your family in a year. Find the number of people that live in your village or town. 2020-21 137 WATER You have listed a number of activities for which you use water. Do you think, our water requirement is limited to activities like these? We use wheat, rice, pulses, vegetables and many other food items everyday. We know that some of the fibres that we use for making fabric come from plants. Is water not needed to grow these? Can you think of some more uses of water? Water is used in industries for producing almost all the things that we use. So, we need water not only for our daily activities but also for producing many things. water from a river, spring, pond, well or a hand pump”. Some others might say, “We get water from taps”. Have you ever wondered where water in the taps comes from? Water that we get from taps is also drawn from a lake or a river or a well (Fig. 14.2). It is then supplied through a network of pipes. Fig. 14.2 Water in taps comes from rivers, lakes, borewell or wells Boojho wonders whether people living in different regions of our country get the same amount of water. Are there regions where people do not get adequate amount of water? How do they manage? You may now get an idea of the amount of water needed by your village or town in a year. Paheli wants to tell you that about two glasses of water are required to produce each page of a book. Each of us may be getting water into our homes in different ways. But, finally, all of us get water from the same sources such as ponds, lakes, rivers and wells. We have discussed some of the sources of water. Where does the water come from, to fill these ponds, lakes, rivers and wells? Boojho wants you to imagine a day in your life when water supply through taps is not available. So, you have to fetch it yourself from a far away place. Would you use the same amount of water as on any other day? 14.2 WHERE DO WE GET WATER FROM? Where do you get the water that you use? Some of you may say, “We draw 2020-21 Page 3 136 SCIENCE 14 Water S uppose for some reason your family gets only one bucket of water everyday for a week. Imagine what would happen? Would you be able to cook, clean utensils, wash clothes or bathe? What are the other activities you would not be able to do? What would happen if we do not have easy access to water for a long period of time? Apart from drinking, there are so many activities for which we use water (Fig. 14.1). Do you have an idea about the quantity of water we use in a single day? each activity by you and other family members. You may use a mug, a glass, a bucket or any other container to measure the amount of water used. Fig. 14.1 Uses of water 14.1 HOW MUCH WATER DO WE USE? Activity 1 List all the activities for which you use water in a day. Some activities are listed in Table 14.1. Make a similar table in your notebook. Throughout the day, measure the amount of water used for Table 14.1 Estimation of the amount of water used by your family in a day y t i v i t c A f o t n u o m A d e s u r e t a w g n i k n i r D g n i h s u r B g n i h t a B s l i s n e t u g n i h s a W s e h t o l c g n i h s a W s t e l i o T r o o l f g n i n a e l C r e h t o y n A n i d e s u r e t a w l a t o T y l i m a f a y b y a d a You now have a rough idea as to how much water your family uses in a day. Can you estimate the amount of water used by you for personal cleanliness in a day. Using this information, calculate the amount of water needed by your family in a year. Now, divide this amount by the number of members of your family. This will give an idea of the amount of water needed by one member of your family in a year. Find the number of people that live in your village or town. 2020-21 137 WATER You have listed a number of activities for which you use water. Do you think, our water requirement is limited to activities like these? We use wheat, rice, pulses, vegetables and many other food items everyday. We know that some of the fibres that we use for making fabric come from plants. Is water not needed to grow these? Can you think of some more uses of water? Water is used in industries for producing almost all the things that we use. So, we need water not only for our daily activities but also for producing many things. water from a river, spring, pond, well or a hand pump”. Some others might say, “We get water from taps”. Have you ever wondered where water in the taps comes from? Water that we get from taps is also drawn from a lake or a river or a well (Fig. 14.2). It is then supplied through a network of pipes. Fig. 14.2 Water in taps comes from rivers, lakes, borewell or wells Boojho wonders whether people living in different regions of our country get the same amount of water. Are there regions where people do not get adequate amount of water? How do they manage? You may now get an idea of the amount of water needed by your village or town in a year. Paheli wants to tell you that about two glasses of water are required to produce each page of a book. Each of us may be getting water into our homes in different ways. But, finally, all of us get water from the same sources such as ponds, lakes, rivers and wells. We have discussed some of the sources of water. Where does the water come from, to fill these ponds, lakes, rivers and wells? Boojho wants you to imagine a day in your life when water supply through taps is not available. So, you have to fetch it yourself from a far away place. Would you use the same amount of water as on any other day? 14.2 WHERE DO WE GET WATER FROM? Where do you get the water that you use? Some of you may say, “We draw 2020-21 138 SCIENCE Do you know that about two thirds of the Earth is covered with water? Most of this water is in oceans and seas (Fig. 14.3). The water in the oceans and seas has many salts dissolved in it — the water is saline. So, it is not fit for drinking and other domestic, agricultural and industrial needs. You might have heard the famous lines of the poem “Rime of the Ancient Mariner” written by S.T. Coleridge in 1798: “Water water every where Nor any drop to drink” Here the poet has described the plight of sailors on a ship lost in the ocean. Yet, oceans play an important role in supplying the water that we use. Do you find this surprising? After all, the water that we use is not salty. Many of us live in places far away from the oceans. Does the water supply in these places also depend on the oceans? How does the ocean water reach ponds, lakes, rivers and wells, which supply us water? How come the water from these sources is not saline anymore? Do you remember Activity 6 in Chapter 5 in which water with salt dissolved in it was heated? What did we find? The water evaporated and the salt was left behind. This activity gives us an idea that, on heating, water changes into its vapour. We also realise from this activity, that water vapour does not carry away the salt with it. Water vapours so formed become a part of the air and cannot usually be seen. We also found that heating is essential to convert water into its vapour. However, we have seen that water changes into its vapour also Fig. 14.3 Oceans cover a major part of the earth Fig. 14.4 Clothes drying on a clothes-line That is where the water cycle comes in! 14.3 WATER CYCLE Disappearing Trick of Water How many times have you noticed that water spilled on a floor dries up after some time? The water seems to disappear. Similarly, water disappears from wet clothes as they dry up (Fig. 14.4). Water from wet roads, rooftops and a few other places also disappears after the rains. Where does this water go? 2020-21 Page 4 136 SCIENCE 14 Water S uppose for some reason your family gets only one bucket of water everyday for a week. Imagine what would happen? Would you be able to cook, clean utensils, wash clothes or bathe? What are the other activities you would not be able to do? What would happen if we do not have easy access to water for a long period of time? Apart from drinking, there are so many activities for which we use water (Fig. 14.1). Do you have an idea about the quantity of water we use in a single day? each activity by you and other family members. You may use a mug, a glass, a bucket or any other container to measure the amount of water used. Fig. 14.1 Uses of water 14.1 HOW MUCH WATER DO WE USE? Activity 1 List all the activities for which you use water in a day. Some activities are listed in Table 14.1. Make a similar table in your notebook. Throughout the day, measure the amount of water used for Table 14.1 Estimation of the amount of water used by your family in a day y t i v i t c A f o t n u o m A d e s u r e t a w g n i k n i r D g n i h s u r B g n i h t a B s l i s n e t u g n i h s a W s e h t o l c g n i h s a W s t e l i o T r o o l f g n i n a e l C r e h t o y n A n i d e s u r e t a w l a t o T y l i m a f a y b y a d a You now have a rough idea as to how much water your family uses in a day. Can you estimate the amount of water used by you for personal cleanliness in a day. Using this information, calculate the amount of water needed by your family in a year. Now, divide this amount by the number of members of your family. This will give an idea of the amount of water needed by one member of your family in a year. Find the number of people that live in your village or town. 2020-21 137 WATER You have listed a number of activities for which you use water. Do you think, our water requirement is limited to activities like these? We use wheat, rice, pulses, vegetables and many other food items everyday. We know that some of the fibres that we use for making fabric come from plants. Is water not needed to grow these? Can you think of some more uses of water? Water is used in industries for producing almost all the things that we use. So, we need water not only for our daily activities but also for producing many things. water from a river, spring, pond, well or a hand pump”. Some others might say, “We get water from taps”. Have you ever wondered where water in the taps comes from? Water that we get from taps is also drawn from a lake or a river or a well (Fig. 14.2). It is then supplied through a network of pipes. Fig. 14.2 Water in taps comes from rivers, lakes, borewell or wells Boojho wonders whether people living in different regions of our country get the same amount of water. Are there regions where people do not get adequate amount of water? How do they manage? You may now get an idea of the amount of water needed by your village or town in a year. Paheli wants to tell you that about two glasses of water are required to produce each page of a book. Each of us may be getting water into our homes in different ways. But, finally, all of us get water from the same sources such as ponds, lakes, rivers and wells. We have discussed some of the sources of water. Where does the water come from, to fill these ponds, lakes, rivers and wells? Boojho wants you to imagine a day in your life when water supply through taps is not available. So, you have to fetch it yourself from a far away place. Would you use the same amount of water as on any other day? 14.2 WHERE DO WE GET WATER FROM? Where do you get the water that you use? Some of you may say, “We draw 2020-21 138 SCIENCE Do you know that about two thirds of the Earth is covered with water? Most of this water is in oceans and seas (Fig. 14.3). The water in the oceans and seas has many salts dissolved in it — the water is saline. So, it is not fit for drinking and other domestic, agricultural and industrial needs. You might have heard the famous lines of the poem “Rime of the Ancient Mariner” written by S.T. Coleridge in 1798: “Water water every where Nor any drop to drink” Here the poet has described the plight of sailors on a ship lost in the ocean. Yet, oceans play an important role in supplying the water that we use. Do you find this surprising? After all, the water that we use is not salty. Many of us live in places far away from the oceans. Does the water supply in these places also depend on the oceans? How does the ocean water reach ponds, lakes, rivers and wells, which supply us water? How come the water from these sources is not saline anymore? Do you remember Activity 6 in Chapter 5 in which water with salt dissolved in it was heated? What did we find? The water evaporated and the salt was left behind. This activity gives us an idea that, on heating, water changes into its vapour. We also realise from this activity, that water vapour does not carry away the salt with it. Water vapours so formed become a part of the air and cannot usually be seen. We also found that heating is essential to convert water into its vapour. However, we have seen that water changes into its vapour also Fig. 14.3 Oceans cover a major part of the earth Fig. 14.4 Clothes drying on a clothes-line That is where the water cycle comes in! 14.3 WATER CYCLE Disappearing Trick of Water How many times have you noticed that water spilled on a floor dries up after some time? The water seems to disappear. Similarly, water disappears from wet clothes as they dry up (Fig. 14.4). Water from wet roads, rooftops and a few other places also disappears after the rains. Where does this water go? 2020-21 139 WATER from the fields, roads, rooftops and other land areas. We also discussed in Chapter 5 that to obtain salt, water from the sea is left in shallow pits to let the water evaporate. From where does this water get the heat it needs to evaporate? Let us find out. Activity 2 Take two similar plates. Place one of the plates in sunlight and keep the other under shade. Now, pour equal amount of water in each of the plates (Fig. 14.5). You can use a cap of a bottle to measure water. Make sure that water does not spill over. Observe the two plates after every 15 minutes. Does the water seem to disappear? From which plate does it disappear first? What is the source of heat for this evaporation? During the daytime, sunlight falls on the water in oceans, rivers, lakes and ponds. The fields and other land areas also receive sunlight. As a result, water from all these places continuously changes into vapour. However, the salts dissolved in the water are left behind. In Activity 2, did you find that water also disappeared from the plate kept in the shade, though it could have taken more time? Does the heat from the sunlight reach here? Yes, during the daytime all the air surrounding us gets heated. This warm air provides heat for evaporation of water in the shade. Thus, evaporation takes place from all open surfaces of water. As a result, water vapour gets continuously added to air. However, evaporation of water is a slow process. That is why we rarely notice its loss from a bucket full of water. In sunlight, evaporation takes place faster. On heating water on a burner, its evaporation takes place even faster. Is there any other process through which water vapour gets transferred into air? Loss of Water by Plants You have learnt in Chapter 7 that plants need water to grow. Plants use a part of this water to prepare their food and Fig.14.5 Evaporation of water in sunlight and in shade Boojho has been reading about transpiration. He asked himself - how much water is lost through transpiration by wheat plants that give us one kilogram of wheat? He found out that this is nearly 500 litres, that is, roughly 25 large sized buckets full of water. Can you now imagine the amount of water lost by plants of all the forests, crops and grasslands together? 2020-21 Page 5 136 SCIENCE 14 Water S uppose for some reason your family gets only one bucket of water everyday for a week. Imagine what would happen? Would you be able to cook, clean utensils, wash clothes or bathe? What are the other activities you would not be able to do? What would happen if we do not have easy access to water for a long period of time? Apart from drinking, there are so many activities for which we use water (Fig. 14.1). Do you have an idea about the quantity of water we use in a single day? each activity by you and other family members. You may use a mug, a glass, a bucket or any other container to measure the amount of water used. Fig. 14.1 Uses of water 14.1 HOW MUCH WATER DO WE USE? Activity 1 List all the activities for which you use water in a day. Some activities are listed in Table 14.1. Make a similar table in your notebook. Throughout the day, measure the amount of water used for Table 14.1 Estimation of the amount of water used by your family in a day y t i v i t c A f o t n u o m A d e s u r e t a w g n i k n i r D g n i h s u r B g n i h t a B s l i s n e t u g n i h s a W s e h t o l c g n i h s a W s t e l i o T r o o l f g n i n a e l C r e h t o y n A n i d e s u r e t a w l a t o T y l i m a f a y b y a d a You now have a rough idea as to how much water your family uses in a day. Can you estimate the amount of water used by you for personal cleanliness in a day. Using this information, calculate the amount of water needed by your family in a year. Now, divide this amount by the number of members of your family. This will give an idea of the amount of water needed by one member of your family in a year. Find the number of people that live in your village or town. 2020-21 137 WATER You have listed a number of activities for which you use water. Do you think, our water requirement is limited to activities like these? We use wheat, rice, pulses, vegetables and many other food items everyday. We know that some of the fibres that we use for making fabric come from plants. Is water not needed to grow these? Can you think of some more uses of water? Water is used in industries for producing almost all the things that we use. So, we need water not only for our daily activities but also for producing many things. water from a river, spring, pond, well or a hand pump”. Some others might say, “We get water from taps”. Have you ever wondered where water in the taps comes from? Water that we get from taps is also drawn from a lake or a river or a well (Fig. 14.2). It is then supplied through a network of pipes. Fig. 14.2 Water in taps comes from rivers, lakes, borewell or wells Boojho wonders whether people living in different regions of our country get the same amount of water. Are there regions where people do not get adequate amount of water? How do they manage? You may now get an idea of the amount of water needed by your village or town in a year. Paheli wants to tell you that about two glasses of water are required to produce each page of a book. Each of us may be getting water into our homes in different ways. But, finally, all of us get water from the same sources such as ponds, lakes, rivers and wells. We have discussed some of the sources of water. Where does the water come from, to fill these ponds, lakes, rivers and wells? Boojho wants you to imagine a day in your life when water supply through taps is not available. So, you have to fetch it yourself from a far away place. Would you use the same amount of water as on any other day? 14.2 WHERE DO WE GET WATER FROM? Where do you get the water that you use? Some of you may say, “We draw 2020-21 138 SCIENCE Do you know that about two thirds of the Earth is covered with water? Most of this water is in oceans and seas (Fig. 14.3). The water in the oceans and seas has many salts dissolved in it — the water is saline. So, it is not fit for drinking and other domestic, agricultural and industrial needs. You might have heard the famous lines of the poem “Rime of the Ancient Mariner” written by S.T. Coleridge in 1798: “Water water every where Nor any drop to drink” Here the poet has described the plight of sailors on a ship lost in the ocean. Yet, oceans play an important role in supplying the water that we use. Do you find this surprising? After all, the water that we use is not salty. Many of us live in places far away from the oceans. Does the water supply in these places also depend on the oceans? How does the ocean water reach ponds, lakes, rivers and wells, which supply us water? How come the water from these sources is not saline anymore? Do you remember Activity 6 in Chapter 5 in which water with salt dissolved in it was heated? What did we find? The water evaporated and the salt was left behind. This activity gives us an idea that, on heating, water changes into its vapour. We also realise from this activity, that water vapour does not carry away the salt with it. Water vapours so formed become a part of the air and cannot usually be seen. We also found that heating is essential to convert water into its vapour. However, we have seen that water changes into its vapour also Fig. 14.3 Oceans cover a major part of the earth Fig. 14.4 Clothes drying on a clothes-line That is where the water cycle comes in! 14.3 WATER CYCLE Disappearing Trick of Water How many times have you noticed that water spilled on a floor dries up after some time? The water seems to disappear. Similarly, water disappears from wet clothes as they dry up (Fig. 14.4). Water from wet roads, rooftops and a few other places also disappears after the rains. Where does this water go? 2020-21 139 WATER from the fields, roads, rooftops and other land areas. We also discussed in Chapter 5 that to obtain salt, water from the sea is left in shallow pits to let the water evaporate. From where does this water get the heat it needs to evaporate? Let us find out. Activity 2 Take two similar plates. Place one of the plates in sunlight and keep the other under shade. Now, pour equal amount of water in each of the plates (Fig. 14.5). You can use a cap of a bottle to measure water. Make sure that water does not spill over. Observe the two plates after every 15 minutes. Does the water seem to disappear? From which plate does it disappear first? What is the source of heat for this evaporation? During the daytime, sunlight falls on the water in oceans, rivers, lakes and ponds. The fields and other land areas also receive sunlight. As a result, water from all these places continuously changes into vapour. However, the salts dissolved in the water are left behind. In Activity 2, did you find that water also disappeared from the plate kept in the shade, though it could have taken more time? Does the heat from the sunlight reach here? Yes, during the daytime all the air surrounding us gets heated. This warm air provides heat for evaporation of water in the shade. Thus, evaporation takes place from all open surfaces of water. As a result, water vapour gets continuously added to air. However, evaporation of water is a slow process. That is why we rarely notice its loss from a bucket full of water. In sunlight, evaporation takes place faster. On heating water on a burner, its evaporation takes place even faster. Is there any other process through which water vapour gets transferred into air? Loss of Water by Plants You have learnt in Chapter 7 that plants need water to grow. Plants use a part of this water to prepare their food and Fig.14.5 Evaporation of water in sunlight and in shade Boojho has been reading about transpiration. He asked himself - how much water is lost through transpiration by wheat plants that give us one kilogram of wheat? He found out that this is nearly 500 litres, that is, roughly 25 large sized buckets full of water. Can you now imagine the amount of water lost by plants of all the forests, crops and grasslands together? 2020-21 140 SCIENCE retain some of it in their different parts. Remaining part of this water is released by the plants into air, as water vapour through the process of transpiration. Do you remember observing transpiration of water by plants in Activity 4 in Chapter 7? Water vapour enters the air through the processes of evaporation and transpiration. Is it lost for ever? No, we get it back again, as we will see. How are clouds formed? Activity 3 Take a glass half filled with water. Wipe the glass from the outside with a clean piece of cloth. Add some ice into the water. Wait for one or two minutes. Observe the changes that take place on the outer surface of the glass (Fig.14.6). From where do water drops appear on the outer side of the glass? The cold surface of the glass containing iced water, cools the air around it, and the water vapour of the air condenses on the surface of the glass. We noticed this process of condensation in Activity 7 in Chapter 5. Fig. 14.6 Drops of water appear on outer surface of the glass containing water with ice The process of condensation plays an important role in bringing water back to the surface of earth. How does it happen? As we go higher from the surface of the earth, it gets cooler. When the air moves up, it gets cooler and cooler. At sufficient heights, the air becomes so cool that the water vapour present in it condenses to form tiny drops of water called droplets. It is these tiny droplets that remain floating in air and appear to us as clouds (Fig. 14.7). It so happens that many droplets of water come together to form larger sized Paheli has noticed dew on leaves of grass on winter mornings. Did you notice something similar on leaves or metal surfaces like iron grills and gates on a cold morning? Is this also due to condensation? Do you see this happening on hot summer mornings? Fig. 14.7 Clouds Ice Water droplets 2020-21Read More
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