Sorting Materials Into Groups

4Sorting Materials into Groups4.1 OBJECTS AROUNDUSWe have seen that our food and clotheshave so much variety in them. Not justfood and clothes, there is such a vastvariety of objects everywhere. We seearound us, a chair, a bullock cart, acycle, cooking utensils, books, clothes,toys, water, stones and many otherobjects. All these objects have differentshapes, colours and uses (Fig. 4.1).Look around and identify objectsthat are round in shape. Our list mayinclude a rubber ball, a football and aglass marble. If we include objects thatare nearly round, our list could alsoinclude objects like apples, oranges, andan earthen pitcher (gharha). Supposewe were looking for objects that areedible. We might include all the itemsthat we have listed in Tables 1.1, 1.2and 1.3 in Chapter 1. We might alsofind that some of those round shapedobjects we just listed out, are also inthis group.Let us say, we wish to make a groupof objects that are made of plastics.Buckets, lunch boxes, toys, watercontainers, pipes and many suchobjects, may find a place in this group.There are so many ways to group objects!In the above examples we have groupedobjects on the basis of their shape or thematerials they are made from.All objects around us are made of oneor more materials. These materials maybe glass, metal, plastics, wood, cotton,paper, mud or soil. Can you think ofmore examples of materials?Activity 1Fig. 4.1 Objects around usLet us collect as many objects aspossible, from around us. Each of uscould get some everyday objects fromhome and we could also collect someobjects from the classroom or fromoutside the school. What will we havein our collection? Chalk, pencil,notebook, rubber, duster, a hammer,nail, soap, spoke of a wheel, bat,26SCIENCE2020-21

matchbox, salt, potato. We can also listobjects that we can think of, but, cannotbring to the classroom. For example,wall, trees, doors, tractor, road.Separate all objects from thiscollection that are made from paper orwood. This way we have divided all objectsinto two groups. One group has theobjects that are made from paper or woodwhile the other group has the objectsthat are not made of these materials.Similarly, we could separate the thingsthat are used for preparing food.Let us be a little more systematic. Listall objects collected, in Table 4.1. Try toidentify the materials that each one ismade of. It would be fun to make this alarge table – collecting informationabout as many objects as possible. Itmay seem difficult to find out thematerials out of which some of theseobjects are made. In such cases, discusswith your friends, teacher and parentsto identify the materials.Boojho wants to know, whetherwe found some materials thatwere used for making more thanone type of an object.Column 1 that are known to you. Now,try and think of everyday objects youknow, that are made mainly of thesematerials, and list them in Column 2.Table 4.2 Different types of objectsthat are made from the samematerialMaterialChair, table,plough, bullock cartand its wheels, .PaperBooks, notebooks,newspaper, toys,calendars,.PlasticsCottonMaterials they aremade of, glass, plasticsPlate (thali) (Satneyelother)PenWoodLeatherTable 4.1 Objects and the materialsthey are made ofObjectsObjects made ofthese materialsPlastics, metalActivity 2Table 4.2 lists some common materials.You can also add more materials inWhat do we find from these tables?First, we grouped objects in manydifferent ways. We then found thatobjects around us are made of differentmaterials. At times, an object is made ofa single material. An object could alsobe made of many materials. And thenagain, one material could be used formaking many different objects. Whatdecides which material should be usedSORTING MATERIALS INTO GROUPS272020-21

for making any given object? It seemsthat we need to know more aboutdifferent materials.4.2 PROPERTIES OF MATERIALSHave you ever wondered why a tumbleris not made with a piece of cloth? Recallour experiments with pieces of cloth inChapter 3 and also keep in mind thatwe generally use a tumbler to keep aliquid. Therefore, would it not be silly,if we were to make a tumbler out of cloth(Fig 4.2)! What we need for a tumbler isglass, plastics, metal or other suchmaterial that will hold water. Similarly,it would not be wise to use paper-likematerials for cooking vessels.Fig. 4.2 Using a cloth tumblerWe see then, that we choose amaterial to make an object dependingon its properties, and the purpose forwhich the object is to be used.So, what are all the properties ofmaterials that would be important fortheir usage? Some properties arediscussed here.AppearanceMaterials usually look different fromeach other. Wood looks very differentfrom iron. Iron appears different fromcopper or aluminium. At the same time,there may be some similarities betweeniron, copper and aluminium that are notthere in wood.Activity 3Collect small pieces of different materials –paper, cardboard, wood, copper wire,aluminium sheet, chalk. Do any of theseappear shiny? Separate the shinymaterials into a group.Now, observe as the teacher cuts eachmaterial into two pieces and look at thefreshly cut surface (Fig. 4.3). What doyou notice? Does the freshly cut surfaceof some of these materials appear shiny?Include these objects also in the groupof shiny materials.Do you notice such a shine or lustrein the other materials, cut them anywayas you can? Repeat this in the class withas many materials as possible and makea list of those with and without lustre.Instead of cutting, you can rub thesurface of material with sand paper tosee if it has lustre.Fig. 4.3 Cutting pieces of materials to see if theyhave lustre28SCIENCE2020-21

Materials that have such lustre areusually metals. Iron, copper, aluminiumand gold are examples of metals. Somemetals often lose their shine andappear dull, because of the action of airand moisture on them. We therefore,notice the lustre, only on their freshlycut sur face. When you visit anironsmith or a workshop, look out forfreshly cut surfaces of metal rods to seeif they have lustre.beakers. Fill each one of them about twothirds with water. Add a small amount(spoonful) of sugar to the first glass,salt to the second and similarly, addsmall amounts of the other substancesinto the other glasses. Stir the contentsof each of them with a spoon. Wait for afew minutes. Observe what happens tothe substances added to water (Fig. 4.4).Note your observations as shownin Table 4.3.HardnessWhen you press different materials withyour hands, some of them may be hardto compress while others can be easilycompressed. Take a metal key and tryto scratch with it, the surface of a pieceof wood, aluminium, a piece of stone, anail, candle, chalk, any other materialor object. You can easily scratch somematerials, while some cannot bescratched so easily. Materials which canbe compressed or scratched easily arecalled soft while some other materialswhich are difficult to compress are calledhard. For example, cotton or sponge issoft while iron is hard.In appearance, materials can havedifferent properties, like lustre,hardness, be rough or smooth. Can youthink of other properties that describethe appearance of a material?Soluble or Insoluble?Activity 4Collect samples of some solid substancessuch as sugar, salt, chalk powder, sandand sawdust. Take five glasses orFig. 4.4 What disappears, what doesn’t?Table 4.3 Mixing different solidmaterials in waterSubstanceSaltDisappears in water/does not disappearDisappears completely inwaterSugarSandChalkpowderSawdustYou will notice that some substanceshave completely disappeared ordissolved in water. We say that thesesubstances are soluble in water. Othersubstances do not mix with water anddo not disappear even after we stir for aSORTING MATERIALS INTO GROUPS292020-21

long time. These substances areinsoluble in water.Water plays an important role in thefunctioning of our body because it candissolve a large number of substances.Do liquids also dissolve in water?We notice that some liquids getcompletely mixed with water. Someothers do not mix with water and forma separate layer when kept aside forsome time.Activity 5Collect samples of vinegar, lemon juice,mustard oil or coconut oil, kerosene orany other liquid. Take a glass tumbler.Fill it up to half with water. Add a fewspoonfuls of one liquid to this and stirit well. Let it stand for five minutes.Observe whether the liquid mixes withwater (Fig. 4.5). Repeat the same withother liquids, as many different liquidsas are available to you. Write yourobservations in Table 4.4.Table 4.4 Solubility of somecommon liquids in waterMixes well/Does not mixLiquidVinegarMixes wellLemon juiceMustard oilCoconut oilKerosene(a)(b)Fig. 4.5 (a) Some liquids mix well withwater while (b) some others do notBoojho suggests that wealso check if the liquids that weused in Activity 5, mix well withsome liquid other than water.Paheli is curious to knowwhether gases also dissolvein water.Some gases are soluble in waterwhereas others are not. Water, usually,has small quantities of some gasesdissolved in it. For example, oxygen gasdissolved in water is very important forthe survival of animals and plants thatlive in water.Objects may float or sink inwaterWhile doing Activity 4, you might havenoticed that the insoluble solidsseparated out from water. You may havealso noticed this with some liquids inActivity 5. Some of these materials thatdid not mix with water, floated to thesurface of water. Others may have sunkto the bottom of the tumbler, right? Wenotice many examples of objects thatfloat in water or sink (Fig. 4.6). Driedleaves fallen on the surface of a pond, astone that you throw into this pond, few30SCIENCE2020-21

Figure 4.6 Some objects float in water whileothers sink in itdrops of honey that you let fall into aglass of water. What happens to allof these?Boojho would like you to give himfive examples each, of objects that floatand those that sink in water. Whatabout testing these same materials tosee if they float or sink in other liquidslike oil?hide behind a glass window? Obviouslynot, as your friends can see through thatand spot you. Can you see through allthe materials? Those substances ormaterials, through which things can beseen, are called transparent (Fig. 4.7).Glass, water, air and some plastics areexamples of transparent materials.Shopkeepers usually prefer to keepbiscuits, sweets and other eatables intransparent containers of glass orTransparencyYou might have played the game of hideand seek. Think of some places whereyou would like to hide so that you arenot seen by others. Why did you choosethose places? Would you have tried toFig. 4.8 Transparent bottles in a shopplastic, so that buyers can easily seethese items (Fig. 4.8).On the other hand, there are somematerials through which you are notable to see. These materials are calledopaque. You cannot tell what is keptin a closed wooden box, a cardboardcarton or a metal container. Wood,cardboard and metals, are examples ofopaque materials.Do we find that we can group allmaterials and objects, without anyconfusion, as either opaque ortransparent?Activity 6Fig. 4.7 Looking through opaque, transparent ortranslucent materialTake a sheet of paper and look throughit towards a lighted bulb. Make a noteof your observation. Now, put 2-3 dropsSORTING MATERIALS INTO GROUPS312020-21