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2 2.1 OBJECTS AROUND Sorting Materials into Groups US We have seen that our food and clothes Let us say, we wish to make a group have so much variety in them. Not just of objects that are made of plastics. food and clothes...

2 2.1 OBJECTS AROUND Sorting Materials into Groups US We have seen that our food and clothes Let us say, we wish to make a group have so much variety in them. Not just of objects that are made of plastics. food and clothes, there is such a vast Buckets, lunch boxes, toys, water variety of objects everywhere. We see containers, pipes and many such around us, a chair, a bullock cart, a objects, may find a place in this group. cycle, cooking utensils, books, clothes, There are so many ways to group objects! toys, water, stones and many other In the above examples we have grouped objects. All these objects have different objects on the basis of their shape or the shapes, colours and uses (Fig. 2.1). materials they are made from. Look around and identify objects All objects around us are made of one that are round in shape. Our list may or more materials. These materials may include a rubber ball, a football and a be glass, metal, plastics, wood, cotton, glass marble. If we include objects that paper, mud or soil. Can you think of are nearly round, our list could also more examples of materials? include objects like apples, oranges, and Activity 1 an earthen pitcher (gharha). Let us collect as many objects as possible, from around us. Each of us could get some everyday objects from home and we could also collect some objects from the classroom or from outside the school. What will we have in our collection? Chalk, pencil, notebook, rubber, duster, a hammer, nail, soap, spoke of a wheel, bat, matchbox, salt, potato. We can also list objects that we can think of, but, cannot bring to the classroom. For example, wall, trees, doors, tractor, road. Separate all objects from this collection that are made from paper or Fig. 2.1 Objects around us wood. This way we have divided all objects Rationalised 2023-24 into two groups. One group has the objects that are made from paper or wood Boojho wants to know, whether while the other group has the objects we found some materials that that are not made of these materials. were used for making more than Similarly, we could separate the things one type of an object. that are used for preparing food. Let us be a little more systematic. List all objects collected, in Table 2.1. Try to identify the materials that each one is made of. It would be fun to make this a Table 2.2 Different types of objects large table – collecting information that are made from the same about as many objects as possible. It material may seem difficult to find out the materials out of which some of these Material Objects made of these materials objects are made. In such cases, discuss with your friends, teacher and parents Chair, table, Wood plough, bullock cart to identify the materials. and its wheels,... Table 2.1 Objects and the materials Books, notebooks, Paper newspaper, toys, they are made of calendars,... Leather Objects Materials they are made of Plastics Steel, glass, plastics Cotton Plate (thali) (any other) Pen Plastics, metal What do we find from these tables? First, we grouped objects in many different ways. We then found that objects around us are made of different Activity 2 materials. At times, an object is made of Table 2.2 lists some common materials. a single material. An object could also You can also add more materials in be made of many materials. And then Column 1 that are known to you. Now, again, one material could be used for try and think of everyday objects you making many different objects. What know, that are made mainly of these decides which material should be used materials, and list them in Column 2. for making any given object? It seems 12 SCIENCE Rationalised 2023-24 that we need to know more about Appearance different materials. Materials usually look different from 2.2 PROPERTIES OF MATERIALS each other. Wood looks very different from iron. Iron appears different from Have you ever wondered why a tumbler copper or aluminium. At the same time, is not made with a piece of cloth? Keep in mind that we generally use a tumbler there may be some similarities between iron, copper and aluminium that are not to keep a liquid. Therefore, would it not there in wood. be silly, if we were to make a tumbler out of cloth (Fig 2.2)! What we need for Activity 3 a tumbler is glass, plastics, metal or Collect small pieces of different materials – other such material that will hold water. paper, cardboard, wood, copper wire, Similarly, it would not be wise to use aluminium sheet, chalk. Do any of these paper-like materials for cooking vessels. appear shiny? Separate the shiny We see then, that we choose a materials into a group. material to make an object depending Now, observe as the teacher cuts each material into two pieces and look at the freshly cut surface (Fig. 2.3). What do you notice? Does the freshly cut surface of some of these materials appear shiny? Include these objects also in the group of shiny materials. Do you notice such a shine or lustre in the other materials, cut them anyway as you can? Repeat this in the class with as many materials as possible and make a list of those with and without lustre. Instead of cutting, you can rub the surface of material with sand paper to see if it has lustre. Fig. 2.2 Using a cloth tumbler on its properties, and the purpose for which the object is to be used. So, what are all the properties of materials that would be important for their usage? Some properties are discussed here. Fig. 2.3 Cutting pieces of materials to see if they have lustre SORTING MATERIALS INTO GROUPS 13 Rationalised 2023-24  Materials that have such lustre are beakers. Fill each one of them about two- usually metals. Iron, copper, aluminium thirds with water. Add a small amount and gold are examples of metals. Some (spoonful) of sugar to the first glass, metals often lose their shine and salt to the second and similarly, add appear dull, because of the action of air small amounts of the other substances and moisture on them. We therefore, into the other glasses. Stir the contents notice the lustre, only on their freshly of each of them with a spoon. Wait for a cut sur face. When you visit an few minutes. Observe what happens to ironsmith or a workshop, look out for the substances added to water (Fig. 2.4). freshly cut surfaces of metal rods to see Note your observations as shown if they have lustre. in Table 2.3. Hardness When you press different materials with your hands, some of them may be hard to compress while others can be easily compressed. Take a metal key and try to scratch with it, the surface of a piece of wood, aluminium, a piece of stone, a nail, candle, chalk, any other material Fig. 2.4 What disappears, what doesn’t? or object. You can easily scratch some Table 2.3 Mixing different solid materials, while some cannot be materials in water scratched so easily. Materials which can be compressed or scratched easily are Substance Disappears in water/ called soft while some other materials does not disappear which are difficult to compress are called Disappears completely in Salt hard. For example, cotton or sponge is water soft while iron is hard. Sugar In appearance, materials can have Sand different properties, like lustre, hardness, be rough or smooth. Can you Chalk powder think of other properties that describe the appearance of a material? Sawdust Soluble or Insoluble? You will notice that some substances have completely disappeared or Activity 4 dissolved in water. We say that these Collect samples of some solid substances substances are soluble in water. Other such as sugar, salt, chalk powder, sand substances do not mix with water and and sawdust. Take five glasses or do not disappear even after we stir for a 14 SCIENCE Rationalised 2023-24 long time. These substances are We notice that some liquids get insoluble in water. completely mixed with water. Some Water plays an important role in the others do not mix with water and form functioning of our body because it can a separate layer when kept aside for dissolve a large number of substances. some time. Do liquids also dissolve in water? Activity 5 Collect samples of vinegar, lemon juice, Boojho suggests that we mustard oil or coconut oil, kerosene or also check if the liquids that we any other liquid. Take a glass tumbler. used in Activity 5, mix well with Fill it up to half with water. Add a few some liquid other than water. spoonfuls of one liquid to this and stir Paheli is curious to know it well. Let it stand for five minutes. whether gases also dissolve Observe whether the liquid mixes with in water. water (Fig. 2.5). Repeat the same with other liquids, as many different liquids as are available to you. Write your Some gases are soluble in water observations in Table 2.4. whereas others are not. Water, usually, Table 2.4 Solubility of some has small quantities of some gases common liquids in water dissolved in it. For example, oxygen gas dissolved in water is very important for Mixes well/ Liquid Does not mix the survival of animals and plants that live in water. Vinegar Mixes well Objects may float or sink in Lemon juice water Mustard oil While doing Activity 4, you might have Coconut oil noticed that the insoluble solids separated out from water. You may have Kerosene also noticed this with some liquids in Activity 5. Some of these materials that did not mix with water, floated to the surface of water. Others may have sunk to the bottom of the tumbler, right? We notice many examples of objects that (a) (b) float in water or sink (Fig. 2.6). Dried Fig. 2.5 (a) Some liquids mix well with leaves fallen on the surface of a pond, a water while (b) some others do not stone that you throw into this pond, few SORTING MATERIALS INTO GROUPS 15 Rationalised 2023-24  hide behind a glass window? Obviously not, as your friends can see through that and spot you. Can you see through all the materials? Those substances or materials, through which things can be seen, are called transparent (Fig. 2.7). Glass, water, air and some plastics are Fig. 2.6 Some objects float in water while others examples of transparent materials. sink in it Shopkeepers usually prefer to keep drops of honey that you let fall into a biscuits, sweets and other eatables in glass of water. What happens to all transparent containers of glass or of these? Boojho would like you to give him five examples each, of objects that float and those that sink in water. What about testing these same materials to see if they float or sink in other liquids like oil? Transparency Fig. 2.8 Transparent bottles in a shop You might have played the game of hide plastic, so that buyers can easily see and seek. Think of some places where these items (Fig. 2.8). you would like to hide so that you are On the other hand, there are some not seen by others. Why did you choose materials through which you are not those places? Would you have tried to able to see. These materials are called opaque. You cannot tell what is kept in a closed wooden box, a cardboard carton or a metal container. Wood, cardboard and metals, are examples of opaque materials. Do we find that we can group all materials and objects, without any confusion, as either opaque or transparent? Activity 6 Take a sheet of paper and look through Fig. 2.7 Looking through opaque, transparent or it towards a lighted bulb. Make a note translucent material of your observation. Now, put 2-3 drops 16 SCIENCE Rationalised 2023-24 of some oil and spread it on the sheet of whether palm of your hand is opaque, paper. Look again towards the lighted transparent or translucent? bulb through that portion of the paper We learnt that materials differ in their on which the oil has been spread. Do appearance and the way they mix in you find that the bulb is more clearly water or other liquids. They may float visible than before? But, can you see or sink in water or may be transparent, clearly through the oiled paper? Is opaque or translucent. Materials can be everything on the other side of it visible? grouped on the basis of similarities or Perhaps not. The materials through differences in their properties. which objects can be seen, but not Why do we need to group materials? clearly, are known as translucent. In everyday life, we often group materials Remember the oily patch on paper when for our convenience. At home, we we tested food items for presence of fats? usually store things in such a manner That was translucent too. Can you that similar objects are placed together. think of some more examples of Such an arrangement helps us to locate translucent materials? them easily. Similarly, a grocer usually We can therefore group materials as keeps all type of biscuits at one corner opaque, transparent and translucent. of his shop, all soaps at another while Paheli suggests grains and pulses are stored at some covering the glass other place. of a torch with your There is another reason why we find palm at a dark such grouping useful. Dividing place. Switch on materials in groups makes it convenient the torch and to study their properties and also observe the other observe any patterns in these properties. Fig. 2.9 Does torch light pass through side of the palm. We will study more about this in your palm? She wants to know higher classes. Hard Opaque Insoluble Rough Lustre Soluble Material T ranslucent Metals T ransparent SORTING MATERIALS INTO GROUPS 17 Rationalised 2023-24  Objects around us are made up of a large variety of materials. A given material could be used to make a large number of objects. It is also possible that an object could be made of a single material or of many different types of materials. Different types of materials have different properties. Some materials are shiny in appearance while others are not. Some are rough, some smooth. Similarly, some materials are hard, whereas some others are soft. Some materials are soluble in water whereas some others are insoluble. Some materials such as glass, are transparent and some others such as wood and metals are opaque. Some materials are translucent. Materials are grouped together on the basis of similarities and differences in their properties. Things are grouped together for convenience and to study their properties. 1. Name five objects which can be made from wood. 2. Select those objects from the following which shine: Glass bowl, plastic toy, steel spoon, cotton shirt 3. Match the objects given below with the materials from which they could be made. Remember, an object could be made from more than one material and a given material could be used for making many objects. Objects Materials Book Glass Tumbler Wood Chair Paper T oy Leather Shoes Plastics 4. State whether the statements given below are True or False. (i) Stone is transparent, while glass is opaque. (ii) A notebook has lustre while eraser does not. (iii) Chalk dissolves in water. (iv) A piece of wood floats on water. 18 SCIENCE Rationalised 2023-24  (v) Sugar does not dissolve in water. (vi) Oil mixes with water. (vii) Sand settles down in water. (viii) Vinegar dissolves in water. 5. Given below are the names of some objects and materials: Water, basket ball, orange, sugar, globe, apple and earthen pitcher Group them as: (a) Round shaped and other shapes (b) Eatables and non eatables 6. List all items known to you that float on water. Check and see if they will float on an oil or kerosene. 7. Find the odd one out from the following: a) Chair, Bed, Table, Baby, Cupboard b) Rose, Jasmine, Boat, Marigold, Lotus c) Aluminium, Iron, Copper, Silver, Sand d) Sugar, Salt, Sand, Copper sulphate SUGGESTED ACTIVITY 1. You may have played a memory game with your friends. Several objects are placed on a table, you are asked to observe them for a few minutes, go into another room and write down the names of all objects that you can remember. Play this game, with a difference! Ask all the participants in the game to remember objects with some particular property while playing this memory game — remember and write down the names of objects that were made of wood or objects that are edible and so on. Have fun! 2. From a large collection of materials, make groups of objects having different properties like transparency, solubility in water and other properties. In later chapters you will also learn about properties of materials related to electricity and magnetism. After making different groups from the collected materials, try and find out if there are any patterns in these groups. For instance, do all materials which have lustre conduct electricity? SORTING MATERIALS INTO GROUPS 19 Rationalised 2023-24