5 materials

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UNIT FIV

MATERIALS


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CLASSIFICATION OF MATERIALS

1) There are many types of materials around us.


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ABILITY TO CONDUCT ELECTRICITY

1) All metals can conduct electricity.

2) It will allow current to flow through it andlight up the bulb.

3) Others materials such as wood, plastic,rubber and glass can not conduct electricity.


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ABILITY TO CONDUCT HEAT

1) Metals are good heat conductors.

2) A good heat conductors will become hot veryquickly on heating.

3) Wood, plastic, rubber and glass are poorconductors of heat.

4) Materials which do not conduct heat well areknown as insulators.


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ABILITY TO FLOAT ON WATER

1) Light materials will float on water.

2) Objects made from wood, plastic and rubberwill float on water.

3) Materials that float are used for makingboats and floats.


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ABILITY TO ABSORB WATER1) Wood has the ability to absorbs water

because it has holes which allow water toenter.2) Objects made from wood such as tissue

paper and paper can absorb water or are

absorbent materials.3) Objects made from cotton such as towels are

also absorbent.4) These materials become wet when in contact

with water, so they are suitable for dryingwet surfaces.

5) Thus cotton cloth is suitable for making

clothes since it can absorb sweat.


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6) Materials which cannot absorb water areknown as non-absorbent materials.

7) Non-absorbent materials used for makingobjects which prevent us from getting wetsuch as raincoats, tents and umbrellas.


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ELASTIC OR NON-ELASTIC1) The ability of a material to return to its

original shape and size after being bent,twisted, stretched or squeezed is known aselasticity.

2) Rubber bands and springs are materials which

are elastic.


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ALLOW OR DON NOT ALLOW LIGHTTO PASS THROUGH

1) Some materials allow light to pass throughthem but some do not.

2) Materials such as glass and plastic allow light

to pass through them, we can see the objectsplaced behind such a material by lookingthrough it.

4) Materials such as wood, metal and rubber do

not allow light to pass through them, wecannot see on object placed behind such amaterial.


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CONDUCTORS AND INSULATORS

1) Materials that allow electricity to flowthrough them are called conductors.

2) Materials that do not allow electricity toflow through them are called insulators.

3) All metals are conductors.4) Non-metals such as wood, plastic, glass andrubber are insulators.

5) A good conductor of electricity is also a good

conductor of heat.6) Conductors are used to make electrical

appliances such as electric irons, kettles andother electronic components.


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7) Insulators are used for covering conductorssuch as cables and electrical appliances such

as the radio and television and as handles forfrying pans.

8) Some daily objects which are conductors andinsulators are:

CONDUCTOR INSULATORNail

Copper wire

Paper clipAluminum foil

Coins

Eraser

Plastic ruler

PaperWooden block

Glass


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B) Translucent Materials1) Materials that scatter light and allow some

light to pass through them.

2) These materials do not allow us to see veryclearly objects behind them. Objects that wesee are blurred.

3) Materials such as tracing paper, tinted glassand ice are examples of translucent materials.

C) Opaque Materials1) Materials that do not allow any light to pass

through them.2) These materials do not allow us to seeobjects behind them.

3) Examples of opaque objects are wooden

objects, books, stones and carbon paper.


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USES OF MATERIALS

A) WOOD1) Comes from tree trucks.

2) Is lighter than most metals but is strong.3) Is a flexible material since it can be easily

shaped to make various objects.


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