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Published by IMAX, 2020-02-13 01:11:41



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SCIENCE 4 TEXTBOOK – 2 Name: ___________________________________ Section: ________________ Roll No.: _________ School: __________________________________

Preface ClassKlap partners with schools, supporting them with learning materials and processes that are all crafted to work together as an interconnected system to drive learning. Our books strive to ensure inclusiveness in terms of gender and diversity in representation, catering to the heterogeneous Indian classroom. ClassKlap presents the Traveller series, designed specifically to meet the requirements of the new curriculum released in November 2016 by the Council for the Indian School Certificate Examinations (CISCE). Guiding principles: The 2016 CISCE curriculum states the following as its guiding principles for Science:  Theme-based learning  Relating science learning to the daily-life experiences of students  Focus on skill/process development  Providing opportunities for knowledge construction  Infusion of environmental issues into the content Each of these principles resonates with the spirit in which the ClassKlap textbooks, workbooks and teacher companion books have been designed. The ClassKlap team of pedagogy experts has carried out an intensive mapping exercise to create a framework based on the CISCE curriculum document. Key features of ClassKlap Traveller series:  Theme-based content that holistically addresses all the learning outcomes specified by CISCE curriculum  Opportunities for experimentation, analysis and synthesis of ideas and concepts  Exposure to locally relevant environmental problem solving  Focus on science-specific vocabulary building  Promotion of participatory and contextualised learning through the engagement of all relevant stakeholders in the learning process All in all, the Traveller Science books aim to enhance the learning of science, development of scientific temper and curiosity towards scientific activities along with the inculcation of healthy habits for environmental protection. – The Authors

Textbook Features • Use of simple, age-appropriate language • Activity-based approach to learning • Use of infographics and pictures to explain concepts and terms • Focus on subject-related vocabulary building I Think I Will Learn About • Introduces the concept/ • Lists the key learning subtopic in a manner as to outcomes of the lesson arouse curiosity and interest among students ? In-text Questions Pin-Up-Note • Oral discussion questions to check for learning and to • H ighlights the key points or gauge the understanding definitions level of the child Connect the Dots A Be Amazed • F osters interdisciplinary • Fascinating facts and trivia thinking by connecting other related to the concept subjects to an aspect of the taught concept Inside the Lab A Note to Parent • H ands-on experience • E ngaging activities to be done provided for creating, at home along with parents to designing or implementing reinforce the concept something innovative and/or useful based on the concept learnt

Contents 7 Composition of Air ���������������������������������������������������������������������������������������....1 8 Solutes, Solvents and Solutions �������������������������������������������������������������������....6 Inside the Lab − B ���������������������������������������������������������������������������������������������� .�12 Activity B1: Balloon Rockets Activity B2: Water as a Universal Solvent 9 Properties of Light �����������������������������������������������������������������������������������������14 10 Measurement ������������������������������������������������������������������������������������������������22 11 Force and Its Effects �������������������������������������������������������������������������������������28 12 Friction and Its Effects������������������������������������������������������������������������������������34 Inside the Lab − C �������������������������������������������������������������������������������������������������40 Activity C1: The Sun Tells the Time Activity C2: Measuring Things Around Us

7Lesson Composition of Air I Will Learn About • the composition of air. • the importance of air to living things. • air pollution. • the measures to keep air clean. I Think Arjun woke up early in the morning to go to school. He found that the air was fresh and cool. When he came back from the school in the afternoon, he felt the air was not as fresh and cool as it was in the morning. Do you know why? Let us revise the properties of air we have studied before. • Clean air has no smell, shape and colour. • Air moves around freely and fills up all available spaces. • Air gives shape to things. • Air has weight. • When heated, air expands and moves upward. Have you ever wondered what air contains? Let us learn about the composition of air. 1

The composition of air Oxygen Carbon The air around us is a mixture of dioxide and different gases. It also contains water other gases vapour, some dust and germs. Nitrogen Nitrogen, oxygen and carbon dioxide The composition of air are the main gases present in the air. Air is mostly made up of nitrogen and The air around us oxygen. Carbon dioxide and some contains gases, water other gases are present in smaller vapour, dust and germs. amounts. ? Name any one gas present in air. The importance of air to living things We learnt about the uses Carbon of air in previous classes. dioxide We have learnt about the different components of air. Oxygen Now, let us see how these components are important to us. 1) A ll living things need Absorption and release of gases by plants and animals oxygen to breathe. In the process of breathing, they take in oxygen from the air and give out carbon dioxide. ?2) P lants take in carbon dioxide from the Name the gas that helps in air to make their food. They give out burning. oxygen during this process. D ue to these two processes, the levels of oxygen and carbon dioxide in the air are maintained. What happens to this balance when we cut down trees? 3) O xygen from the air helps in burning. We need to burn different fuels to cook food, light lamps and so on. 2

Be Amazed A As we go higher, the level of oxygen in the air decreases. So, the people who climb mountains carry oxygen cylinders with them. A mountaineer with an oxygen cylinder Air pollution The addition of any harmful substances to air is called air pollution. Substances which make air dirty (or pollute air) are called pollutants. Let us learn where these pollutants come from. 1) D ifferent fuels used at home and in vehicles and factories give out smoke when they burn. The smoke from vehicles and factories may contain many poisonous chemicals. 2) B urning garbage, plastics, crackers, incense sticks (agarbatti), cigarettes and so on releases harmful smoke into the air. 3) T he chemical sprays used at farms, fields and houses to kill harmful insects are another source of pollutants. 4) A ctivities like construction of roads and buildings, and running vehicles blow up dust in the air. 5) U nhealthy activities such as spitting, throwing garbage around, urinating and defecating in the open add disease-causing germs to the air. 6) C  arbon dioxide is useful at very low levels. But when its amount increases above normal levels, it becomes a pollutant. Addition of various pollutants to air Composition of Air 3

Addition of various pollutants to air The measures to keep air clean How can we keep the air clean? 1) W  e should not cut trees. We should plant more trees. They help to maintain the oxygen levels in the air. 2) We should avoid using cooking stoves and lamps that give out smoke. 3) We should not burn garbage in our neighbourhood. 4) V  ehicles that are not maintained give out harmful gases in the form of smoke. We should get our vehicles serviced regularly to reduce air pollution. 5) T o reduce the smoke released by the vehicles on the road, we should use shared taxis or public transport vehicles like buses, trains and so on. This will help to reduce the number of vehicles on the road. We should walk or use a bicycle for shorter distances. 6) We should use fuels such as CNG or LPG, or other sources of energy such as electric or solar energy. 7) W e should avoid using chemical sprays to kill harmful insects. We can use the extracts of some plants like neem to kill insects. 8) W e should not spit, urinate, defecate or throw garbage in public places. 9) F actories should filter the smoke to remove the pollutants before releasing it into the air. They should be located away from the places where people live. ? State any one way to reduce air pollution. 4

Connect the Dots English Fun An abbreviation is a short form of any word or a phrase. We can write the names of different gases using short forms (symbols) as given below. Component of air Short form (symbol) Carbon dioxide CO2 Nitrogen N2 Oxygen O2 You will learn about these symbols in higher classes. Social Studies Fun Smoke from factories is harmful to us. So, factories are built in industrial areas far from our homes. Find out whether there is any such area near your city. Smoke from factories A Note to Parent Help your child make a dos and don’ts list to keep the air clean. Also, help them identify the activities in the neighbourhood that lead to air pollution. Composition of Air 5

8Lesson Solutes, Solvents and Solutions I Will Learn About • solutes, solvents and solutions. • soluble and insoluble substances. • methods to separate insoluble substances from water. • methods to separate soluble substances from water. I Think Nafisa wants to know why sugar and salt disappear when added to a glass of water and stirred well with a spoon. Can you help her? In Class 3, we learnt that water is a solvent, and it can dissolve most solutes in it to form different types of solutions. Let us learn about solutes, solvents and solutions in detail. Solutes, solvents and solutions In our day-to-day life, we make mixtures of many substances. For example, we mix curry with rice, lime juice with water, sugar with milk and so on. What happens after we mix two or three substances? Some of them form a mixture, where we can see all the things we mixed. For example, if we mix lentils and rice grains, we can see both of them in the mixture. But, in some other mixtures, one or more of the things may not be visible. For example, if we mix sugar and salt with water, we can see only water. The sugar and the salt dissolve in the water and disappear. 6

A mixture in which one or more substances are dissolved in another substance is called a solution. The substance that gets dissolved is called the += solute. The substance in which the solute dissolves is called the solvent. ? What do we call the substance that Solvent Solute Solution gets dissolved in another substance? Water is the most common solvent we use in our A solution is formed day-to-day life. Water can dissolve different types of when one or more solutes in the solid, liquid or even gaseous forms. solutes get dissolved in a solvent. Let us see some more examples of solutes, solvents and solutions in our day-to-day life. We add some sugar to milk and stir it before drinking. Sugar dissolves in the milk. Here, the sugar is a solute and the milk is a solvent. You must have had lemon, mango or amla sherbets on hot summer days. They are the solutions of salt, sugar and the juice of the fruit in water. The aerated soft drinks we drink have carbon dioxide dissolved in water. All the water bodies have oxygen dissolved in water. You must have seen tea getting prepared in your ? Name any one solute. house. We add milk, tea powder and sugar in water and boil it to make tea. Do all these things dissolve in water? After making the tea, we filter it. The tea powder does not dissolve in water. It only adds colour and taste. Soluble and insoluble substances Substances that dissolve in a solvent are called soluble substances, and those that do not dissolve are called insoluble substances. Try this! You will need: seven glasses, water, cooking oil, common salt, sugar, baking soda, jeera, talcum powder and glucose. You need to: Take the samples of these substances in separate glasses, and mix them with water as well as oil one by one. Find out which of them are soluble in water and which ones in oil. Note them down. Solutes, Solvents and Solutions 7

Substance added Dissolves/does not dissolve in Dissolves/does not dissolve in sugar water cooking oil baking soda common salt jeera sand glucose talcum powder Sugar, baking soda, common salt and glucose dissolve in water. Jeera, sand and talcum powder do not dissolve. None of these substances dissolve in cooking oil. In the above activity, we have mixed many ? Name any one substance substances in water. Can we separate them insoluble in water. from the water again? How can we do it? Methods to separate insoluble substances from water Let us learn about some methods to separate insoluble substances from water. Sedimentation and decantation: In this method, the Sedimentation Water insoluble substances are allowed to settle down by Sand and keeping the liquid undisturbed for some time. For mud example, sometimes, we get muddy water in the rainy season. This muddy water is kept undisturbed in a Sand and container so that all the insoluble impurities (sand and mud mud) settle down at the bottom. Clear water Decantation can be carried out after sedimentation. In this process, the upper layer of water is poured into another container without disturbing the substances settled at the bottom. For example, the particles of mud from the muddy water that settle down in the process of sedimentation are separated using decantation. Decantation 8

Filtration: In this method, a mixture having insoluble impurities is filtered through a filter paper like we filter tea or coffee at home. The impurities remain Mixture on the filter paper and thus, get separated from the liquid. For example, we can separate insoluble particles of mud or sand from water using a filter paper. Funnel Sedimentation, Filter paper decantation and Water filtration are methods used to separate Filtration insoluble substances from water. Methods to separate soluble substances from water Can we separate the sugar dissolved in water using sedimentation, decantation or filtration? No. Dissolved substances do not settle at the bottom and pass through filters along with the water. So, we use another method called vaporisation to separate such soluble substances from water. Solvent Vaporisation is the process of turning a liquid vapour into its vapour form. It is used to separate solutes dissolved in water. Vaporisation can be done in two ways: evaporation and boiling. At normal temperature, during evaporation, Solution water turns into vapour leaving behind the Heat dissolved substances. During boiling, we need to provide additional Boiling heat to turn the water into vapour. For example, if we take a solution of common salt in water and boil it, the water from the solution turns into vapour leaving behind small crystals of common salt. Evaporation and boiling ? What is vaporisation? can be used to separate soluble substances from water. Solutes, Solvents and Solutions 9

Be Amazed A The common salt we use at home is obtained from Separation of salt from seawater by using the process of evaporation. Seawater seawater consists of large amounts of salt. It is collected in salt pans on the seashore. The water from the salt pans evaporates due to the Sun’s heat leaving behind heaps of common salt. Connect the Dots Maths Fun Represent the following data using tally marks. Substances soluble in water = 8 Substances soluble in oil = 6 Insoluble substances = 2 S.No. Data Tally marks 1) Substances soluble in water = 8 2) Substances soluble in oil = 6 3) Insoluble substances = 2 10

English Fun Give meanings. 1) solute: _______________________________________________________________________ 2) insoluble: ____________________________________________________________________ 3) sedimentation: ______________________________________________________________ A Note to Parent Help your child to check the water solubility of different substances used at home and list their observations in the table given below. Water-soluble substances Water-insoluble substances Solutes, Solvents and Solutions 11

B Inside the Lab Make sure you do these activities only with the help of a teacher or an adult. Activity B1: Balloon Rockets You have learnt about some properties of air. Now, let us do an activity to demonstrate one of the properties of air. You will need: a balloon, a kite string or any other thick string, a plastic straw, sticking tape and a pair of scissors. You need to: 1) Take a piece of kite string. 2) T ie one end of the string to a chair, a doorknob or any other strong support. 3) P ut the other end of the string through a straw. Stretch the string and tie it to some other strong support. 4) B low up a balloon (do not tie it with a thread or knot). Pinch the end of the balloon so that no air escapes. 5) T hen, stick the balloon to the straw using some pieces of sticky tape as shown below in the picture. Hold the opening of the balloon to your side while doing this, and let no air escape from the balloon. Your balloon rocket is ready for launch. Now let the balloon go, and watch how it goes along the string. The balloon rocket moves forward as the air rushing out of the balloon gives it a push. 12

Activity B2: Water as a Universal Solvent We know that water is called a universal solvent as it dissolves more substances than any other liquid. Let us find out which of the given household items it will dissolve. You will need: four glasses of clean water, spoons, baking soda, pepper, flour and washing powder. You need to: 1) L ine up four glasses of water. Put one teaspoon of each substance into a separate glass each. 2) T ry to dissolve each of the substances by stirring using a spoon. 3) R  ecord your observations in the table given below. (Note: Do not try to put too much of any substance in the water.) Observation table: Name of the substance Dissolves/does not dissolve baking soda pepper flour washing powder Inside the Lab – B 13

9Lesson Properties of Light I Will Learn About • the sources of light – natural and artificial. • luminous and non-luminous objects. • the properties of light. • transparent, translucent and opaque objects. • shadow formation. I Think Ronak was playing with a ball inside his house. The ball slipped out of the window and fell somewhere outside the house. When he stepped outside the house, his parents told him to take a torch as it was already dark outside. He wondered why we cannot see things around in darkness. Do you know why? We can see things around us when light falls on them. We learnt in previous classes that the Sun gives us light during the daytime. At night, we get light from the Moon, lamps, bulbs and so on. They are sources of light. Let us learn about the different sources of light in detail. The sources of light – natural and artificial There are two types of light sources: 1) natural sources 2) artificial sources (made by human beings) 14

Natural sources: The Sun and the other stars are natural sources of light. The Sun is the main source of light for us. As other stars are far away from us, we get very little light from them compared to the Sun. We get moonlight during The stars The Sun Firefly night time. But, the Moon does not have light of its own. It appears bright due to the sunlight that falls on it. Some small animals can also give out light. For example, fireflies and glow worms. Artificial sources: The artificial sources of light are made by humans. They include electric bulbs, kerosene lamps, oil lamps, candles and so on. Electric bulb Kerosene lamp Oil lamp Candle ? Name the main source of natural light Sources of light are on Earth. of two types: natural and artificial. Properties of Light 15

Be Amazed A Atolla is a jellyfish that lives in the deep sea. When attacked by its enemies, it gives out flashes of light. Atolla jellyfish We have learnt about different sources of light. We know that not all objects around us can be used as a source of light. What kind of objects are used as light sources? Let us see. Luminous and non-luminous objects Objects that can give out light Luminous objects on their own are known as luminous objects. For example, the Sun, electric bulbs, oil lamps, candles and so on. Objects that do not give out light The Sun Electric bulb on their own are known as non- luminous objects. For example, the Moon, tables, books, pencils, bags and so on. Non-luminous objects Table Book Pencil ? Which object is luminous: Luminous objects give a stone or a bulb? out light on their own, and non-luminous objects do not give out light on their own. 16

The properties of light Light has the following properties: 1) T  he light from a source travels in all directions. For example, when we switch on a bulb, the light spreads to all corners of the room. 2) L ight travels very fast. This is why the moment we switch on a bulb, light reaches all corners of the room. 3) L ight travels in a straight line. Let us do an activity Light travels in all directions to see this. Try this! You have to do this activity in a dark room. You will need: a cardboard box and a lighted torch You need to: T ake a cardboard box. Make a hole on one side. Now, place a lighted torch inside the box, facing the side of the box that has the hole. Make sure that the light of the torch comes out only through the hole. Observe the light coming out through the hole. What do you see? Now, place a cardboard piece in its way. Does the light reach the other side of the cardboard? What do we understand from this experiment? Light travels in a straight line. 4) W hen we place any object in the path of light, the light hits it and bounces back. This is called the reflection of light. When this reflected light from any object reaches our eyes, we see that object. This is the reason why we need light to see objects. 5) When light that travels through air enters water or any other liquids, the direction of the light changes. This change in the direction of light when moving from one medium to another is called the refraction of light. Reflection of light Properties of Light 17

Try this! You need a spoon and a glass half filled with water. Place a spoon in a glass of water. Observe the part of the spoon Spoon appears near the water surface. It appears bent near the water surface. bent inside water Now, take out the spoon, and check. You can see that there is no actual bend in the spoon at all. It appears bent because of the refraction of light. 6) T he light we see is white in colour. But it can be split into seven different colours – violet, indigo, blue, green, yellow, orange and red (VIBGYOR). R ainbows are formed in this way by the splitting of white light into seven colours. We can split white light Rainbow Splitting of light using a glass prism. We have learnt that light travels in a straight line. What happens to light when different objects come in its path? Let us find out. Transparent, translucent and opaque objects Try this! You will need: 1) a glass bottle, a coloured, glass bottle and a black, plastic bottle. 2) a torch You need to: Light the torch and place its mouth inside each bottle, and check how much light comes out through the bottle. What do you find? The glass bottle allows the light to pass through it. Such objects are called transparent objects. Another example is water. We can see through transparent objects. We use transparent objects to make spectacles, window panes, aquariums and so on. The coloured bottle allows only a part of light to pass through it. Such objects are called translucent objects. Have you seen sunglasses? They are translucent. We use them during sunny days to prevent bright light reaching our eyes. The black, plastic bottle does not allow light to pass through it at all. Such objects are called opaque objects. 18

Other examples are wood, book, blackboard and so on. We cannot see through opaque objects. This is why people use opaque objects like wood and bricks to make the walls of houses. Glass is transparent Coloured plastic bottles are Walls are opaque translucent ? Name a transparent object. Shadow formation When an object blocks the path of light, a dark area is formed behind that object. This dark area is called a shadow. Transparent objects allow light to pass through them. They do not block the light. So, they do not form shadows. Translucent objects allow only some light to pass through them. They can Shadow formation form shadows, but they are not very dark. Opaque objects block the path of light completely and form dark shadows. A shadow is a dark Shadows are always formed opposite to the source of light. area formed when an object blocks the path of light. Connect the Dots English Fun Using a dictionary, find out the different meanings of the word ‘light’. Properties of Light 19

Maths Fun A room has 10 luminous objects, 15 transparent objects, 12 translucent objects and 20 opaque objects. Represent this using tally marks. Object Tally marks 10 luminous objects 15 transparent objects 12 translucent objects 20 opaque objects A Note to Parent With the help of the following activity, help your child understand the concept of light and shadow. You will need: • d ifferent objects like plate, book, glass, mirror, comb, clothes, plastic box, paper and so on. • a torch You need to: 1) darken the room completely. No light should come in. 2) switch on the torch. 3) n ow, take the objects one-by-one, and hold them in front of the torchlight. Let the shadow form on the wall in front. 4) a sk your child to identify which objects block light and which allow it to pass through them. 20

You can also try some shadow puppets with your child at home. Bear Goat Rabbit Dog Bird Elephant Camel Duck Wolf Properties of Light 21

10Lesson Measurement I Will Learn About • the need for measurement in daily life. • instruments and units used for measurement and how to use them. I Think One day, Soumya could not go to school as she had fever. Her mother took her to a doctor. The doctor put a pen-like thing in her mouth for some time. Do you know what it was? Why did he put that thing in her mouth? The instrument that the doctor kept in Soumya’s mouth is a thermometer. It is used to measure our body heat (temperature). What are the other things we measure in our day-to-day life? Why do we need to measure things? Let us find out. The need for measurement in daily life Measurement is the action of measuring Every day, we need to keep a track of time to do different or finding out the activities. For example, time to go to school, lunchtime, time quantity or amount to play in the evening, dinner time, bedtime and so on. For of something. this, we need to measure time. 22

If we want to know how long or short a pencil is, we have to measure its length. In the same way, if we want to check how tall we are, we need to measure our height. To buy anything from the market, we need to find the count or weight of things. To understand how far or near a place is, we need to measure the distance. We measure things to find their length, breadth, height, weight, amount and so on. How do we measure things? If we have to find out how many pencils we have, we count them. But, can we count the water inside a bottle? No. So, to measure different things, we need different units and instruments. Let us learn about some of them. Instruments and units used for measurement and how to use them Ruler and measuring tape: These are the instruments that are used to measure length and height. The units we use to measure length and height are millimetre (mm), centimetre (cm), metre (m) and kilometre (km). 10 mm is equal to 1 cm; 100 cm is equal to 1 m, and 1000 m is equal to 1 km (or 10 mm = 1 cm; 100 cm = 1 m; 1000 m = 1 km). We use a ruler to measure the length of objects such as pencils, boxes, tables, books and so on. Has your mother ever taken you to Ruler a tailor to get your clothes stitched? What does a tailor use to measure the size of your arms, waist or legs? They use a measuring tape. If we look closely at a ruler or measuring tape, we can see markings on it. These markings represent the units of measurement. On a ruler, we can see millimetre and centimetre markings. Let us see how to use a ruler to measure the length of a pencil. 1) Keep the ruler along the pencil. 2) Align one end of the pencil to the zero mark of the ruler. 3) Check the marking on the ruler at the other end of the pencil. Measuring tape Measurement 23

4) The reading at the other end of the pencil is the length Millimetre (mm), of the pencil. centimetre (cm), metre (m) and kilometre We can measure the length of any object with a (km) are the units measuring tape in a similar manner. to measure length and height. A ruler or ? Name one instrument that is used to measure measuring tape is used the length of an object. to measure length and height. Weighing machine and weighing balance: We measure the weight of an object using a weighing machine or weighing balance. The units to measure weight are milligram (mg), gram (g) and kilogram (kg). 1000 mg is equal to 1 g, and 1000 g is equal to 1 kg (or 1000 mg = 1 g; 1000 g = 1 kg). Let us learn how to use a weighing machine to measure weight. 1) Place the weighing machine on a flat, level surface in order Weighing to obtain readings as correct as possible. machine 2) Check that the needle of the weighing scale is at zero. ?Then, stand straight on the weighing What do we use to measure body weight? machine. The reading on the weighing scale is your weight. A weighing balance has two pans and a needle. To measure the weight of an object using a weighing balance, we use standard weights. Depending on the weight of the objects we keep on the pans, the needle turns to the right, left or remain vertical. The needle points towards the side which has more weight. When both the sides have equal weight, the needle remains vertical. Let us now learn how to use a weighing balance. Standard weights 1) Inthe first pan, keep the object that needs to be weighed. 2) Inthe second pan, keep standard weights of Milligram (mg), gram (g) and different amounts. kilogram (kg) are the units to measure weight. A weighing 3) The weights in the second pan are changed machine or a weighing till the needle becomes vertical. The weight balance is used to measure that makes the needle vertical is the weight weight. of the object. 24

Thermometer: We measure temperature using a thermometer. It tells how cold or hot an object is. The units of measurement for temperature are Degrees Fahrenheit (°F) and Degrees Celsius (°C). A thermometer has a mercury-filled column. As per the temperature, the level of the mercury falls or rises. Let us learn how to use a thermometer to measure the temperature of our body. 1) Shake the thermometer well. Check the mercury Thermometer level. When it falls to 35°C or below, put it under the tongue or the armpit, and wait for one minute. 2) Take out the thermometer and read the temperature. Rotate the thermometer to be able to see the mercury level clearly. The mercury level shows the reading of temperature. If the lining ends at 37, the temperature is 37°C. Nowadays, digital thermometers are more commonly used. Upon placing under the tongue or armpit for a minute, they show the reading on a digital display. Clock: We know that people tell time with the help of a watch or clock. Do you know how to read the time using a clock or a watch? A clock measures time in units of seconds, minutes and hours. Digital thermometer Look at the clock given below. It has three hands. They move around the clock and show the time. The short hand is called the hour hand. The long hand is called the minute hand. The thin, fast-moving hand is the second hand. Can you see the numbers and the markings of the clock in the given picture? The time the second hand takes to move from one small marking to the next marking is one second. We can see 60 such markings on the clock. So, the second hand makes one complete circle in 60 seconds. 60 seconds make one minute. So, whenever the second hand completes one circle, the minute hand moves one mark ahead. The minute hand completes one complete circle in 60 minutes. This makes one hour. The numbers written on the dial show hours. By the time the minute hand completes one circle, the hour hand moves to the next number. Clock Measurement 25

dHow do we tell time looking at a clock? 1) First, we look at the hour hand. In the clock given above, it is at 10, which equals to 10 hours (10 o’clock). 2) Then, we check the position of the minute hand. It is at the 10th marking, which equals to 10 minutes. 3) Lastly, we look at the second hand. It is at the 32nd marking, which equals to 32 seconds. 4) So, the time is 10 hours 10 minutes and 32 seconds. We say it as 10 minutes and 32 seconds past 10 o’clock. Be Amaze A In olden times, people in our country used the length of arms and the width of fingers as the units of length. Instead of standard weights, they used the weight of some seeds as the unit of measurement. Connect the Dots English Fun Make nouns from the following words. 1) measure: ________________________________________________________________ 2) weighing: ________________________________________________________________ 3) read: ____________________________________________________________________ 4) long: ____________________________________________________________________ 26

Maths Fun 1000 grams make 1 kilogram. Convert 4 kilograms into grams. 4 kilograms = 4 x 1000 grams = __________________ grams A Note to Parent Take your child along with you to the grocery store. Let them observe the weights and weighing balances or weighing machines used by the shopkeeper. Measurement 27

11Lesson Force and Its Effects I Will Learn About • push and pull and their effects. • different types of forces in day-to-day life. I Think Living things can move from one place to another on their own. Non-living things around us cannot move on their own from one place to another. How do we make them move? To make any object move, we either push or pull it. Let us learn about push and pull in detail. Push and pull and their effects Look at the given picture. To move a cart, we need to either push or pull it. When we push an object, we hold it and try to move it forward. A girl pushing a cart The object moves away from us. Following are some examples: • We push a door away from us to open or close it. • We push a striker while playing carrom. • We push a ball with a racket while playing tennis. • We push a cart in a mall. 28

While pulling, we move the object towards ourselves. Following are some examples of pulling. • W e pull a door towards ourselves to open or close it. • W  e pull our socks up while getting ready for school. • W  hile playing tug of war, we pull a rope towards ourselves. • In a bullock cart, the bull pulls the cart towards itself. Pulling is the opposite of pushing. A pull or push that makes an object move is called force. We apply force to make things move. Is there any other way force is helpful to us? Let us Force is a push find out. or pull acting on What do you do to stop while riding a bicycle? We use brakes. an object. Through the brakes, we are applying force to stop the wheels from rolling. So, force helps us to stop a moving object. Pulling rope while playing tug of war Children riding bicycles We also use force to make an object move faster or slower. When we apply more force (push or pull), objects move faster. When we apply less force (push or pull), objects move slower. When you open a door, if you push or pull it very lightly, the door will not open. But if you do it with greater strength, the door opens. If you push or pull the door too hard, it slams into the wall. Force is also needed to change the direction of a moving object. A batsman needs force to change the direction of a ball by hitting it with his bat. ? What is force? Force and Its Effects 29

Try this! 1) Take a plastic bottle without a cap. Crush it. Its shape will change. 2) Pull the two edges of a sheet of paper in the opposite direction. It will tear. 3) Take a fully blown balloon, and press it. It will burst. What do we understand from this activity? We can tear, break or change the shape of objects by applying a force. So let us see again what we have learnt about force. 1) Force can make an object move. 2) Force can make a moving object stop. 3) F orce can change the speed (increase or decrease) of a moving object. 4) F orce can change the direction of a moving object. 5) Force can change the shape of an object. Different types of forces in day-to-day life We have learnt that we apply force to move, stop or change the shapes of things. Some forces act all the time in nature. Let us learn about them. Gravitational force: Sometimes, objects may move or stop without anyone applying any push or pull, for example, rain. Do we pull the raindrops towards the ground? No, they are pulled towards the ground by some other force. In the same way, the ball that we throw upwards comes back down without anyone pulling it. The force that pulls down objects Ball falling on the ground towards the Earth is called gravity or gravitational force. ? Which force pulls objects towards the centre of the Earth? 30

Be Amaze d A Each planet in the solar system has its own force of gravity. Some have a very strong gravitational force, and others have a weak one. Frictional force: Friction is the force that acts against the movement of objects. Let us see how this happens. Try this! Take two blocks of wood: one with smooth Contact area Box edges and the other with rough edges. Force Surface Now, slide both of them on the floor one after the other applying the same amount Friction of force. What do you see? The block with smooth edges moves faster and for a longer distance. The other one does not move that far. This is because of the frictional force that acts against the moving block. Objects with a rough surface develop more friction. The smoother the surface, the lesser the friction. The force that acts Frictional force acting whenever any two against the moving block objects rub together or are in contact is called ? Name a force that always acts against frictional force. the movement of objects. Magnetic force: Have you ever played with a magnet? Have you noticed that it gets stuck on your refrigerator? It can also attract objects like key rings, iron nails and iron paper clips towards itself. Can you tell why? A magnet attracting paper clips Force and Its Effects 31

This is because a magnet has the power to pull certain A man lifting a box using metals such as iron and nickel towards itself. So, things made the muscles of his arms of these metals get attracted to it. This attraction force of a magnet is called magnetic force. Muscular force: It is the force applied by the muscles of our body to do various kinds of work. We use muscular force to run, walk, stand, sit, push, pull, carry things and so on. Connect the Dots English Fun An acrostic poem is a kind of poem in which the first, last or any other letter of each line together form a word. Look at the example of an acrostic poem for the word ‘school’. SUPER COOL HAPPY ON TIME OUTDOOR PLAY LEARNING Write an acrostic poem, where the first letters of the lines form the word FORCE. F ____________________________________________________________________________ O ____________________________________________________________________________ R ____________________________________________________________________________ C ____________________________________________________________________________ E ____________________________________________________________________________ 32

Social Studies Fun Sir Isaac Newton, who lived from 1643–1727, discovered gravity when he saw a falling apple while thinking about the forces of nature. A Note to Parent Try out the different activities given in the lesson with your child at home. Help them understand the concept of force using these activities. Force and Its Effects 33

12Lesson Friction and Its Effects I Will Learn About • friction in daily life. • uses of friction. • harmful effects of friction. • ways to reduce friction. I Think Roy was oiling his hair. He spilt some oil on the floor. His mother asked him to immediately wipe it off as someone may slip on it. Roy wondered why floors become slippery when oil is spilt on them. Do you know why? In the previous lesson, we learnt that friction is a type of force that acts against the movement of objects. Let us learn more about friction and its importance in our lives. Friction in daily life A ball rolling on the floor Let us do an activity to understand the use of friction in our daily life. Take a ball and roll it on the floor. The force you applied made the ball move. What happens next? The ball stops after a while. Which force acts upon the ball to stop it? This is the force of friction. 34

The friction between the surfaces of Push the ball and the floor acts against the movement of the ball and stops it. Friction develops when an object is in touch with a surface. So, we call it a contact force. Let us discuss a few more situations from our day-to-day life in which we experience the force of friction. While sliding down a slide, have you ever Friction felt your movement being slowed down? Friction acting against Sometimes you get stuck halfway! This is the motion of an object because of the force of friction between you and the slide. Friction is a contact We experience friction when we push or drag things over a force. It acts against surface. Friction is developed even when we write or draw the motion of objects on any surface, walk or run, ride a bicycle and so on. in contact with a surface and slows ? Name a contact force that acts down or stops their against movement. movement. What causes friction? Playing on a slide Riding bicycles Carrying luggage Writing on a blackboard Friction is caused by the bumps on the two surfaces which are in contact. Rough surfaces have a lot of tiny grooves and bumps. So they develop more friction. You like to play with your toy car. It runs very smoothly when you roll it on a floor. Try to roll it on a carpet. You will find it difficult. It is because the carpet’s surface is not smooth, and it creates more friction. Friction and Its Effects 35

Try this! Rub your palms against each other for some time. Now, touch your cheeks with your palms. What do you feel? They have become warm. This is due to friction. Friction between surfaces produces heat. Friction helps us in many ways in our day-to-day life. Let us discuss some of them. Uses of friction Friction helps us hold objects tight. When we hold an object with our hand, there is friction acting between our fingers and the object. Due to the friction, the object does not slip out of our hand. It helps us to walk on the floor without slipping. Friction between the soles of shoes and the surface of the ground helps us to run. Friction helps us to hold objects Friction helps us to walk and run We can easily light a matchstick Friction helps to light Friction helps vehicles because of friction. When we rub a matchstick to run on road the matchstick against the sides of a matchbox, due to the friction, heat is produced. This heat helps the matchstick to light. Friction between the tyres of vehicles and the surfaces of roads helps the vehicles to run on roads smoothly. Friction between the surface of our notebook and the tip of our pencil or pen helps us to write on the notebook. Friction between the edges of a saw, Friction helps us to write Friction helps us to cut a knife or a pair of scissors and the objects objects to be cut helps us to cut the objects properly. 36

? State two uses of friction. Harmful effects of friction Friction is not always useful to us. It may also cause wear and tear of the surfaces of the objects in contact. Try this! Take an eraser and rub it against any rough surface. What happens to the eraser? The side that was rubbed gets damaged. Some parts may even break. In the same way, parts of machines and vehicles in contact with each other develop wear and tear due to friction. So, they need to be maintained and if required, replaced due to the damage caused by friction. Friction may produce heat in running vehicles. We need to put coolants in vehicles to reduce this heat. When we use the same socks or shoes for many days, the holes that appear in our socks and shoes are because of friction. Friction can cause difficulty in sliding heavy loads across the floor. As friction acts against motion, Friction produces heat in running vehicles vehicles may need more fuel to move when friction is high. Ways to reduce friction We know that friction occurs when two surfaces are in contact. If the surface is smooth, the friction is less. So, friction can be reduced by making the surfaces in contact smoother. We apply powder on carrom boards before Applying powder on a carrom board playing. Can you guess the reason behind this? reduces friction The powder forms a layer between the surfaces and makes them smooth. This helps in the easy movement of the carrom coins. Friction and Its Effects 37

Have you noticed that oil on our hands or any surfaces makes them more slippery? Oil forms a layer over the surface and reduces its roughness. So, the friction becomes low. This is why we oil our bicycle if it does not run smoothly. Substances that reduce friction are called lubricants. Be Amaze Oiling a bicycle A d Friction is developed even when we move in the air and water. Vehicles have specific shapes to reduce the effect of friction. This is why birds, aeroplanes, fish and so on have streamlined shape: to reduce friction caused due to air and water. Connect the Dots English Fun Punctuate the following sentence and rewrite it. the teacher said friction stops the movement of objects ____________________________________________________ ____________________________________________________ ____________________________________________________ ____________________________________________________ 38

Maths Fun Like we measure length in metres and weight in kilograms, friction is measured in a unit called ‘Newton’. A Note to Parent Discuss different examples of friction and its effects in day-to-day life with your child. Friction and Its Effects 39

C Inside the Lab Make sure you do these activities only with the help of a teacher or an adult. Activity C1: The Sun Tells the Time! Have you ever wondered how people in olden times were able to tell time even before clocks were invented? They used the position of the Sun in the sky to tell time. For this, they used sundials. Sundials are the oldest known instruments used for telling time. A sundial works by casting a shadow in different positions and at different times of a day. The surface of a Sundial sundial has markings for each hour of daylight. As the Sun moves across the sky, a sundial casts a shadow on these markings. The position of the shadow shows what time it is. The flat surface of a sundial is called the Gnomon dial plate. A sundial has a part called a gnomon to cast a shadow on the markings Dial on the dial. Shadow of gnomon Let us make our own sundial. You will need: a paper plate, crayons, a sharpened pencil, Parts of a sundial a plastic straw, push pins and a ruler. You need to: 1) Start this project just before 12:00 p.m. on a sunny day. 2) Take a paper plate and put it upside down. 3) T ake your pencil and poke a hole through the centre of the plate. 4) Write the number 12 at the top of the plate with a crayon. 5) D raw a straight line from the number 12 to the centre of the plate. 40

6) O nce it is 12:00 p.m., take the plate and a straw outside. Place the plate on the ground and poke the straw through the centre. 7) F ind a place where the Sun shines all day so that you can leave the sundial in the same position. 8) N ow, turn the plate so that the shadow of the straw runs along the line to the number 12. 9) F asten the plate on the ground with some push pins, and check the sundial an hour later. 10) S et your alarm for the next hours – 1:00 p.m., 2:00 p.m. and so on. When the alarm sounds, observe where the straw’s shadow is on the paper plate. 11) A  lign the ruler with the edge of the straw’s shadow, and make a pencil mark along the edge of the ruler. Make sure you don’t move the paper plate. 12) Write the next hour on the paper plate. 13) R  epeat the observation and note the hour on the plate after each hour. If you started in the afternoon, come back the next day in the morning hours to complete the hour marks. You will notice that as the day went by, the rays from the Sun reached your sundial at different angles, making the straw cast a shadow at different places. By marking the shadows at equal intervals of time, and assigning a number to each segment, you have made your first sundial! Activity C2: Measuring Things Around Us You have studied about the weighing balance that is used to weigh various objects. You might have seen such a balance at grocery shops. Now, let us make a small model of a weighing balance to demonstrate the concept of weighing objects. You will need: a plastic hanger (preferably with notches), thick thread, two empty plastic cups and a pencil or pen. You need to: 1) T ake a plastic cup and make markings at equal distances around its brim to punch holes. Punch three holes at equal distances. Repeat the activity with another plastic cup. Inside the Lab – C 41

2) C ut six pieces of thread of equal length; each around 30 cm long. Tie these pieces of thread in the holes made in the cups. Tie the three pieces together at the top of each cup. These make the weighing pans of your weighing balance. 3) T  ie these cups on either side of a hanger. Now your weighing balance is ready! 4) H old the tip of the hanger in your hand, or hang it from a curtain rod. Both the pans will be at the same level. Now, put some beans in one of the pans and observe what happens. The pan with the beans in it will go down. Now, start putting beans in another pan and continue adding till both the pans come to the same level. What does this mean? The weight of beans in both the pans is nearly the same. 42



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