Materials Around Us
Why This Matters
Look around the room you are in right now.
You will see many things. A chair. A book. A water bottle. A window. Your school bag. Each one of these is an object — a thing you can see and touch.
Now ask one simple question about any of them. What is it made of?
The chair may be made of wood. The bottle may be made of plastic. The window is made of glass. The thing that an object is made of is called its material.
Here is something interesting. Nobody picks a material by chance. A window is made of glass for a reason. A spoon is made of steel for a reason. Nobody makes a glass out of cloth — and there is a clear reason for that too.
In this chapter you will learn what materials are. You will learn the simple ways we can group, or sort, materials. And best of all, you will learn why the right material is chosen for each job. By the end, you will look at everyday things in a brand new way.
The Big Idea
Everything around us is made of some material — like wood, plastic, glass, metal, cloth, or clay. One object can be made of many materials, and one material can make many objects. Different materials behave in different ways: some shine, some are hard, some bend easily, some dissolve in water, some float, some let light pass through. We can group materials by these behaviours, which we call their properties. Once we know a material’s properties, we can choose the right material for the right job.
Let’s Break It Down
Objects vs materials
Let us be very clear about two words first.
An object is a thing. A chair, a ball, a comb, a pencil. You can hold it.
A material is the stuff an object is made of. Wood, plastic, iron, glass, paper, cloth, rubber, clay.
So the chair is the object. The wood is the material.
Here is the first big idea, and it surprises many students.
One object can be made of MANY materials.
Think of a chair. The back may be wood. The seat cushion may be cloth. The legs may be metal. That is one chair — but three different materials in it! A pen is the same. It has a plastic body, a metal tip, and ink inside.
The top half of Figure 6.1 shows this clearly.
Now the second big idea.
One material can make MANY objects.
Think of plastic. From plastic we make a water bottle, a bucket, a comb, a chair, a toy, and many more things. One material, many objects.
The bottom half of Figure 6.1 shows this.
These two ideas go together, so we have put both in one picture. Look at Figure 6.1 below.
So when you see any object, you can ask two things. What materials is it made of? And what other objects could be made from those same materials?
Properties we use to group materials
We know there are many materials. To study them better, we group them. Grouping just means putting similar things together.
We do this all the time. In a kitchen, all the spoons go in one place and all the plates in another. In a shop, all the biscuits are on one shelf and all the soaps on another. Putting similar things together is called classification (sorting into groups).
But to group materials, we need a rule. We group them by their properties. A property is just a way a material behaves or looks.
Let us learn six simple properties, one by one.
Appearance (shiny or dull — lustre)
The first thing you notice about a material is how it looks. Some materials are shiny. Some are dull (not shiny).
When light falls on a shiny material, it gleams. This shine is called lustre. A material that shines is called lustrous.
A new steel spoon shines. A piece of gold shines. A copper wire shines. These shiny materials are usually metals (a group of strong, shiny materials like iron, copper, gold, and aluminium).
Other materials do not shine. Paper, wood, rubber, and cloth are dull, or non-lustrous.
“All that glitters is not gold.”
Not everything shiny is a metal. Sometimes a plain material is coated with a shiny layer to make it look shiny. So shine is a good first clue, but not a sure test.
Hardness (hard or soft)
Some materials are difficult to press or scratch. We call these hard. A stone is hard. Iron is hard. You cannot squeeze them with your fingers.
Some materials are easy to press or scratch. We call these soft. An eraser is soft. A sponge is soft. Cotton is soft. They give way when you press them.
Here is one careful point. Hard and soft are compared to each other. Rubber is harder than a sponge, but rubber is softer than iron. So a material is “hard” or “soft” only when we compare it with something else.
Flexibility (bends or breaks)
Some materials bend easily without breaking. We call these flexible. A rubber band bends. A copper wire bends. A piece of cloth folds. You can change their shape and they do not snap.
Some materials do not bend at all. They are rigid, which means stiff. Glass does not bend — push it too far and it cracks. A wooden ruler is rigid too.
Flexibility helps us pick the right material. A water pipe is often made of flexible plastic so it can bend around corners. A window pane is made of rigid glass so it stays flat and firm.
Solubility in water (dissolves or not)
Take a glass of water. Add a spoon of sugar and stir. The sugar seems to disappear! It mixes fully into the water. We say sugar dissolves in water. A material that dissolves in water is soluble in water.
Now take another glass of water. Add some sand and stir. The sand does not disappear. It just sinks and sits at the bottom. We say sand does not dissolve. A material that does not dissolve is insoluble in water.
Salt is soluble. Chalk powder and sand are insoluble. Figure 6.2 below shows the difference side by side.
This property is very important for our body. Water can dissolve many things, which is how food and medicine travel inside us.
Float or sink in water
Drop different objects into a tub of water and watch.
Some things stay on top of the water. We say they float. A piece of wood floats. A plastic ball floats. A dry leaf floats.
Some things go straight down to the bottom. We say they sink. An iron nail sinks. A stone sinks. A coin sinks.
But what decides this? It is not just how heavy a thing is — it is how heavy it is for its size. Scientists call this density. A big iron ship floats because it is hollow and spread out, so it is light for its size. A small solid iron nail sinks because it is heavy for its size. So a thing floats when it is light for its size, and sinks when it is heavy for its size.
So whether a material floats or sinks is another property we can use to group it. Figure 6.3 below shows both happening in one tub.
Transparency (transparent, translucent, opaque)
This property is about light. It asks one question: can you see through the material?
There are three answers.
If you can see clearly through it, it is transparent. Clear glass is transparent. Clean water is transparent. You can read a book through a clear glass sheet.
If you can see a little, but not clearly — just a blurry, hazy shape — it is translucent. Butter paper is translucent. Frosted glass (the hazy bathroom glass) is translucent. Light gets through, but the picture is fuzzy.
If you cannot see through it at all, it is opaque. A wooden door is opaque. A wall is opaque. A metal sheet is opaque. No picture gets through.
Figure 6.4 below puts the same smiley face behind all three materials, so you can see the difference at a glance.
Let us put these three side by side so the difference is crystal clear.
| Type | Can you see through it? | Examples |
|---|---|---|
| Transparent | Yes, clearly | Clear glass, clean water, air |
| Translucent | A little, but hazy and blurry | Butter paper, frosted glass |
| Opaque | No, not at all | Wood, cardboard, metal, a wall |
Why we group materials
So why do we bother sorting materials at all? There is a very useful reason.
When we know a material’s properties, we can choose the right material for the right job.
Think about it. A window must be transparent, so we pick glass — not wood. A frying pan must take heat and stay hard, so we pick metal — not plastic. A school bag must be soft and light, so we pick cloth — not iron.
Here is the “nothing is a given” question from the start of the chapter. Why is a tumbler (a drinking glass) never made of cloth? Because the job of a tumbler is to hold water. Cloth has tiny gaps in it, so water leaks straight through. Glass, steel and plastic have no gaps, so they hold water. The material must match the job. Figure 6.5 below matches some jobs to the best materials, and shows the wrong choice too.
Let us walk through how to make this choice for one object, step by step.
You need to make a window for a house. The window must let people see outside, must keep out rain, and must be hard enough to stay in the wall. Which material should you choose — cloth, wood, or glass?
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First, list what the job needs. The window must (a) let you see through it, (b) not let rain pass, and (c) be hard and firm.
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Now check cloth. Cloth is soft, and water leaks through it. So cloth fails point (b) and point (c). Cloth is out.
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Now check wood. Wood is hard and keeps out rain, so it passes (b) and (c). But wood is opaque — you cannot see through it. So wood fails point (a). Wood is out.
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Now check glass. Glass is transparent, so you can see through it. Glass does not let rain pass. And glass is hard. So glass passes all three needs.
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So the right material for a window is glass. We chose it by matching the material’s properties to what the job needs.
Before we move on, let us quickly refresh one idea from earlier in this chapter that we just used.
Now a quick “why” check to make sure the main idea has clicked.
Why is a raincoat made of plastic and not of cotton cloth?
Because the job of a raincoat is to keep rain out. Plastic does not let water pass through it, so you stay dry. Cotton cloth soaks up water and lets it through, so you would get wet. The material is chosen to match the job.
A blackboard is made so you cannot see through it. Is it transparent, translucent, or opaque?
It is opaque. Opaque means no light passes through and you cannot see through it at all. A blackboard needs to be opaque so the writing shows up clearly against it.
Common Mistakes
These are the slip-ups students make most often with this chapter. Let us clear them up.
When sugar dissolves in water, it has 'disappeared' and is gone for good.
Your eyes can no longer see the sugar in the clear water, so it feels like it has vanished into nothing.
The sugar has not gone anywhere. It has only broken into tiny bits that spread out and hide among the water. The sugar is still there — that is why the water tastes sweet, and if the water dries up, the sugar comes back.
Heavy things always sink and light things always float.
Many heavy things you have seen, like a big stone, do sink, while light things like a leaf float, so the rule seems to fit.
Floating and sinking depend on how heavy a thing is for its size, not on its total weight alone. A huge iron ship floats because it is hollow and spread out, so it is light for its size. A tiny iron nail sinks because it is solid and heavy for its size.
Everything that shines is a metal.
Most shiny things you handle, like a steel spoon or a coin, really are metals, so shine and metal feel like the same thing.
Shine is only a clue, not proof. A plain plastic or paper item can be coated with a thin shiny layer to make it glitter. As the saying goes, all that glitters is not gold.
Translucent and transparent mean the same thing.
Both words start the same way and both let some light through, so they sound like one idea.
They are different. Through a transparent material you see clearly, like clear glass. Through a translucent material you see only a hazy, blurry shape, like butter paper. The amount you can see is what tells them apart.
Quick Check
Time for a few quick questions. Pick the best answer.
Which of these is a material, not an object?
You add salt to water and stir. The salt mixes in and you cannot see it. What do we call salt here?
Butter paper lets you see a blurry, hazy shape but not a clear picture. Butter paper is:
Why is a frying pan made of metal and not plastic?
Practice Problems
Try each one yourself first. Then tap to check the full answer.
Easy
Name the object and the material in each: (a) a glass tumbler, (b) a wooden table, (c) a cotton shirt.
(a) Object: tumbler. Material: glass.
(b) Object: table. Material: wood.
(c) Object: shirt. Material: cotton (a kind of cloth).
In each one, the first word tells you the material and the second tells you the object.
Sort these into 'dissolves in water' and 'does not dissolve in water': sugar, sand, salt, chalk powder.
Dissolves in water (soluble): sugar, salt.
Does not dissolve in water (insoluble): sand, chalk powder.
If you stir them in water, the sugar and salt mix in and seem to vanish. The sand and chalk powder stay separate and settle down.
Medium
Which will float and which will sink in a bucket of water: a dry wooden spoon, an iron key, a plastic ball, a stone? Group them.
Float: dry wooden spoon, plastic ball.
Sink: iron key, stone.
Wood and plastic float on water, so they stay on top. Iron and stone sink, so they go to the bottom.
A child wants to make a lampshade so that the light from the bulb is soft and not too bright in the eyes. Should the lampshade be transparent, translucent, or opaque? Why?
It should be translucent.
A transparent shade would let all the light through, so the bulb would still be too bright. An opaque shade would block all the light, so the room would be dark. A translucent shade lets some light through but spreads it out and softens it — exactly what we want. So translucent is the right choice.
Challenge
A spoon used to eat hot food is usually made of steel, but its handle is sometimes wrapped in plastic. Explain why two different materials are used for one object.
This object — one spoon — is made of two materials because its two parts have two different jobs.
The bowl part of the spoon touches hot food. It must be hard and must not melt or burn. Steel is hard and handles heat well, so the bowl is made of steel.
The handle is the part you hold in your hand. Steel gets hot quickly and could burn your fingers. Plastic does not get hot so fast, so it is safer to hold. That is why the handle is wrapped in plastic.
So we picked each material to match the job of each part. This shows the big idea again: one object can be made of many materials, each chosen for its properties.
Summary
- An object is a thing you can see and touch. A material is the stuff an object is made of, like wood, plastic, glass, metal, cloth or clay.
- One object can be made of many materials (a chair has wood, cloth and metal). One material can make many objects (plastic makes bottles, buckets and combs).
- Putting similar things into groups is called classification. We group materials by their properties — the ways they look and behave.
- Some materials are shiny (lustrous, usually metals); some are dull. Some are hard; some are soft. Hard and soft are always compared with something else.
- Some materials are flexible — they bend without breaking (rubber band, wire, cloth). Some are rigid, or stiff (glass, a wooden ruler).
- A material that dissolves in water is soluble (sugar, salt). One that does not is insoluble (sand, chalk). Dissolving is not the same as disappearing forever.
- Some materials float on water (wood, plastic) and some sink (iron, stone). Floating does not depend only on weight.
- A material can be transparent (see clearly, like glass), translucent (see hazily, like butter paper), or opaque (cannot see, like wood).
- We group materials so we can choose the right material for each job — glass for a window, metal for a pan, plastic for a raincoat.
What’s Next
You now know that everything around you is made of some material, and you can sort materials by their properties. One property we touched on was whether a thing gets hot — like a metal pan on a fire.
That leads to a new question: how hot is hot? How do we measure heat in numbers? In the next chapter, Chapter 7 — Temperature and its Measurement, you will learn what temperature is and how a thermometer measures it. See you there!
Frequently Asked Questions
What is the difference between transparent translucent and opaque materials?
Transparent materials let all light pass through so you can see clearly through them — clean glass and clear water are examples. Translucent materials let some light through but scatter it so things look blurry — frosted glass and butter paper are translucent. Opaque materials block all light so you cannot see through them at all — wood, metal and brick are opaque.
What does soluble and insoluble in water mean class 6?
When you stir a material into water and it completely mixes in and disappears, it is soluble — salt and sugar are soluble in water. When a material does not mix and stays as separate bits at the bottom or floating on top, it is insoluble — sand and chalk powder are insoluble in water. Solubility is an important property for cooking, medicine and cleaning.
What is the difference between an object and a material?
An object is a specific thing you can see and touch, like a spoon, a bottle or a table. A material is the substance it is made from, like steel, plastic or wood. Many different objects can be made from the same material (steel spoon, steel tray, steel door) and the same object can be made from different materials (a chair can be wooden or plastic).
What properties do we use to group materials class 6?
We group materials by their properties — lustre (does it shine?), hardness (can you scratch it?), flexibility (does it bend without breaking?), solubility in water (does it dissolve?), whether it floats or sinks in water, and transparency (can you see through it?). These properties help us choose the right material for the right job.
Why does a stone sink but a piece of wood float in water?
Whether something floats or sinks depends on how heavy it is for its size — scientists call this density. Stone is very heavy for its size (high density) so it sinks. Most types of wood are lighter for their size (lower density than water) so they float. An object floats when it is less dense than water and sinks when it is more dense.