Natural and man-made materials
A comb, a water bottle, a glass tumbler and a wooden chair at home: some come ready from nature, some are made in factories.
Wood, rock, minerals and water are natural materials (नैसर्गिक पदार्थ). Materials made in factories with the help of laboratory research are man-made materials (मानवनिर्मित पदार्थ), for example glass, plastic, artificial threads and thermocol.
Rule 1: Find the source of a material — Look at what a thing is made of to say whether it is natural or man-made. One article can contain both kinds.
- Easy : The wood in a wooden chair is natural.
- Medium : A comb is plastic, so it is of a man-made material.
- Exam-type : A wooden chair with plastic feet and nails contains both natural and man-made materials.
Rule 2: A classification chart — Write the names of household things, the material used and its kind, and a chart is ready.
- Easy : Broom: coconut-leaf sticks — natural.
- Medium : Water bottle: plastic — man-made.
- Exam-type : Knife: steel (an alloy) with a plastic handle — the man-made part is larger.
Man-made materials are produced from research on natural materials.
Not everything made in a factory is wholly artificial; natural raw material is used.
Memory clue : "Natural = nature, man-made = factory" — see where it is made.
Spot the difference
| Point | Natural | Man-made |
|---|---|---|
| Example | Wood, stone | Glass, plastic |
| Where made | In nature | In a factory |
Practice questions
- 1Name two natural materials.
- 2Name two man-made materials.
- 3Which material is used for a comb?
- 4How are man-made materials made?
- 5Which materials make a broom and a pen?
- 6Can one article have both natural and man-made materials?
- 7"Glass is natural because it is made from sand": why is this wrong?
- 8How would you classify five household things as natural or man-made?
Show answers (try them yourself first)
- 1Wood and stone.
- 2Glass and plastic.
- 3Plastic.
- 4In factories using results of laboratory research.
- 5Broom - coconut-leaf sticks; pen - plastic.
- 6Yes, e.g. a wooden chair with plastic feet.
- 7Sand is natural but glass is made in a factory by processing, so it is man-made.
- 8Check what each is made of and note it in a table.
Types and properties of plastic
A bucket, an electric switch, a cooker handle and a milk bag are all plastic, yet the bucket can be reshaped by heat and the switch cannot.
Plastic (प्लास्टिक) is a man-made material that can be moulded (plasticity). By their reaction to heat plastics are of two kinds: thermoplastic (तापमृदू) and thermosetting (तापदृढ).
Rule 1: Thermoplastic and thermosetting plastic — Thermoplastic softens on heating and can be reshaped (polythene, PVC). Thermosetting plastic, once moulded, keeps its shape even on heating (bakelite, melamine).
- Easy : Toys and combs are made of thermoplastic.
- Medium : Electric switches and cooker handles are thermosetting, so they do not bend with heat.
- Exam-type : An old PVC pipe can be heated and bent, but a bakelite switch does not melt; it only chars.
Rule 2: Properties of plastic — Plastic does not rust or rot easily, is hardly affected by rain or damp, can be of any colour, is light, and is a poor conductor of heat and electricity.
- Easy : A plastic bucket left in the rain is not spoilt.
- Medium : Electric wires have a plastic cover because plastic does not conduct electricity.
- Exam-type : Plastic tanks are used to store chemicals because most chemicals do not act on plastic.
There are over 2000 kinds of plastic, each with different uses.
Thinking that all plastic melts on heating. Thermosetting plastic does not.
Memory clue : "Thermo-soft = reshape, thermo-set = stays" — thermoplastic can be reshaped, thermosetting cannot.
Spot the difference
| Point | Thermoplastic | Thermosetting |
|---|---|---|
| On heating | Softens, can be reshaped | Keeps its shape |
| Example | Polythene, PVC | Bakelite, melamine |
| Use | Toys, combs, bags | Switches, cooker handles |
Practice questions
- 1What are the two kinds of plastic?
- 2Name one thermoplastic.
- 3Name one thermosetting plastic.
- 4Why are electric switches made of thermosetting plastic?
- 5State two properties of plastic.
- 6Why are plastic tanks used for storing chemicals?
- 7Of two combs, one bends on heating and the other does not. Which is of which kind?
- 8Why is "all plastic can be melted and reshaped" wrong?
Show answers (try them yourself first)
- 1Thermoplastic and thermosetting.
- 2Polythene (or PVC).
- 3Bakelite (or melamine).
- 4It does not soften with heat and does not conduct electricity.
- 5Light and does not rust (or a poor conductor of electricity).
- 6Chemicals do not act on plastic.
- 7The bending one is thermoplastic; the other is thermosetting.
- 8The shape of thermosetting plastic does not change even on heating.
Plastic and the environment
Carry bags, milk bags and water bottles come home every day. Where do they go after use?
Materials that rot away naturally are degradable (विघटनशील); those that do not are non-degradable (अविघटनशील). Plastic is non-degradable and so a pollutant.
Rule 1: Time to degrade — Vegetables rot in 1-2 weeks, cotton cloth in about a year, wood in 10-15 years, but plastic needs thousands of years.
- Easy : A thrown banana peel soon rots but a plastic bag stays.
- Medium : Plastic dumped in waste stays in the ground for many generations.
- Exam-type : Burning plastic adds poisonous gases to air, so burning is no solution.
Rule 2: The 4R principle — Reduce (use less), Reuse (use again), Recycle (use again after processing), Recover (reclaim). Cloth, paper and jute bags instead of plastic save the environment.
- Easy : Carrying a cloth bag to the market avoids a plastic bag: Reduce.
- Medium : Using an empty water bottle as a flower pot: Reuse.
- Exam-type : Processing old plastic into new articles: Recycle.
Use less plastic and choose degradable materials where possible.
Thinking that plastic mixes into the soil and vanishes. It lasts for thousands of years.
Memory clue : "4R: Reduce, Reuse, Recycle, Recover" — these four steps save the environment.
Spot the difference
| Point | Degradable | Non-degradable |
|---|---|---|
| Example | Vegetables, cotton, wood | Plastic, glass |
| Effect | Rots into soil | Pollutes for years |
Practice questions
- 1Is plastic degradable or non-degradable?
- 2Name the four R's.
- 3Name two bags that can replace plastic.
- 4What is a degradable material?
- 5Why is burning plastic harmful?
- 6Give one example of Reuse.
- 7Arrange vegetables, wood and plastic in order of increasing time to degrade.
- 8Suggest two ways to reduce plastic waste in your school.
Show answers (try them yourself first)
- 1Non-degradable.
- 2Reduce, Reuse, Recycle, Recover.
- 3Cloth and paper (or jute) bags.
- 4A material that rots away in nature.
- 5Poisonous gases enter the air.
- 6Using an empty bottle as a flower pot.
- 7Vegetables, wood, plastic.
- 8Use cloth bags and reuse old bottles.
Thermocol
A new glass article reaches home packed in a light, white, sponge-like material.
Thermocol (थर्मोकोल) is a form of polystyrene (पॉलिस्टायरीन). It softens with heat and sets again on cooling, so it can be given any shape. It absorbs shocks, so it is used to pack delicate things.
Rule 1: Uses of thermocol — Thermocol is used to pack glass and electrical goods, for decorations, and for plates and cups at large gatherings.
- Easy : A TV box is padded with thermocol pieces.
- Medium : A thermocol layer absorbs the knock so the article does not break.
- Exam-type : Being light, thermocol adds no weight in transport, but it harms the environment.
Rule 2: Harmful effects of thermocol — Thermocol is non-degradable. Burning it releases poisonous gases. Hot food in thermocol plates may take in styrene, which can harm health.
- Easy : Avoid serving hot tea in thermocol cups.
- Medium : Workers in thermocol factories may get eye, breathing and skin problems.
- Exam-type : Burning thermocol waste is no remedy; using less and recycling are the remedies.
Do not keep hot food in thermocol containers.
Thinking thermocol rots naturally. It is non-degradable.
Memory clue : "Light, shock-proof, non-degradable" — remember both the use and the harm.
Spot the difference
| Point | Advantage | Disadvantage |
|---|---|---|
| Weight | Light | — |
| Shock | Absorbs it | — |
| Environment | — | Does not rot, poisonous gases on burning |
Practice questions
- 1From which material is thermocol made?
- 2State one use of thermocol.
- 3Is thermocol degradable?
- 4Why is thermocol good for packing?
- 5Why can thermocol be given any shape?
- 6What happens when thermocol is burnt?
- 7Why should hot tea not be served in thermocol cups?
- 8Write two ways to cut thermocol waste.
Show answers (try them yourself first)
- 1Polystyrene.
- 2Packing delicate things.
- 3No, it is non-degradable.
- 4It absorbs shocks and is light.
- 5It softens with heat and sets on cooling.
- 6Poisonous gases go into the air.
- 7Styrene may mix with the tea and harm health.
- 8Use less and recycle it.
Glass
Window panes, spectacle lenses, bulbs and bangles are all glass, yet each glass is a little different.
Glass (काच) is a hard but brittle, non-crystalline solid made from a mixture of silica and silicates. Silica is sand (SiO₂).
Rule 1: How glass is made — Sand, soda, lime and a little magnesium oxide are heated in a furnace. Sand alone melts near 1700 °C; adding pieces of waste glass lowers the heat needed. After melting, the mix is heated to about 1500 °C and cooled quickly to give clear glass.
- Easy : Reusing old glass pieces saves fuel.
- Medium : Quick cooling prevents crystals from forming, so the glass stays transparent.
- Exam-type : Soda-lime glass is colourless; ferrous oxide gives bluish-green and copper oxide gives red glass.
Rule 2: Properties of glass — Glass softens on heating and can be moulded. It is a poor conductor of heat and electricity and is transparent. Sudden heating or cooling can crack it.
- Easy : A glass of hot tea dipped in cold water may crack.
- Medium : Glass is used as an insulator in electrical fittings.
- Exam-type : If glass contains oxides of chromium, vanadium or iron it absorbs much of the light.
Rule 3: Types and uses of glass — Silica glass goes into laboratory ware, borosilicate glass into medicine bottles, lead glass into bulbs and tubes, optical glass into spectacles and lenses; alkali silicate glass dissolves in water.
- Easy : A laboratory test tube is of silica glass.
- Medium : Medicine bottles are of borosilicate glass because medicines do not act on it.
- Exam-type : Alkali silicate glass, from sand and soda, dissolves in water, so it is called "water glass".
Glass is non-degradable. Broken pieces entering drains or water do harm.
Do not think glass is a liquid; it is a non-crystalline solid.
Memory clue : "Sand + soda + lime → furnace → quick cool" — the order of glass making.
Spot the difference
| Type | Main use |
|---|---|
| Silica glass | Laboratory ware |
| Borosilicate glass | Medicine bottles |
| Lead glass | Bulbs, tubes |
| Optical glass | Spectacles, lenses |
Practice questions
- 1A mixture of which materials gives glass?
- 2Name two properties of glass.
- 3Which glass is called "water glass"?
- 4What is mixed with sand in making glass?
- 5Why is glass cooled quickly?
- 6Which glass is used for medicine bottles?
- 7What problem arises if broken glass goes into drains?
- 8State two benefits of adding old glass pieces to the mixture.
Show answers (try them yourself first)
- 1Silica (sand) and silicates.
- 2Transparent and brittle.
- 3Alkali silicate glass.
- 4Soda, lime and a little magnesium oxide.
- 5So that crystals do not form and the glass stays transparent.
- 6Borosilicate glass.
- 7Glass does not rot, so drains may get blocked.
- 8Less heat is needed, fuel is saved and waste falls.