4.5 Transparent, Translucent and Opaque Materials

1) Depending on whether light can pass through them, materials can be
    classified into 3 groups:
    (a) Transparent materials
    (b) Translucent materials
    (c) Opaque materials
___________________________________________________________

2) Transparent materials allow the most light to pass through.
    (a) Transparent materials can be made of clear glass or clear
          plastic.
    (b) Objects behind a transparent material can be seen clearly.
    (c) Examples: glass, bottle, transparency sheet, light bulb, thermometer,
         beaker, ice, spectacles.
  

                      Windsreen                                                                   Aquarium
___________________________________________________________________

3) Translucent materials allow only some light to pass through.
    (a) Examples of translucent materials are tracing paper, frosted glass
          and certain types of plastic and thin cloth.
    (b) Objects behind a translucent material cannot be seen clearly and
          appeared blurred.
    (c) Othe examples: coloured glass bottle, window pane, plastic bag,
          plastic container.

                                       Frosted glass                                      Lampshade
__________________________________________________________________

4) Opaque materials do not allow any light to pass through.
    (a) A shadow forms behind an opaque material when a light shines
         on it.
    (b) Objects behind an opaque material cannot be seen at all.
    (c) Wood, rubber, metals, some plastics and cloth are opaque materials.
    (d) Examples: wall, hat, clothes, towel, box, paper, bag, book.

                              Umbrella                                                   Wooden door

4.4 Conductors and Insulators

Conductors and Insulators Of Electricity

1) Materials that conduct electricity are called conductors of electricity.

2) Metals such as copper, aluminium, iron, steel and zinc are good
    conductors of electricity.

A iron paper clip is made of iron. The bulb
lights up because electricity flows through
the circuit. Iron is a conductors of electricity.

The wires are made of copper, a good
 conductor of electricity.






3) Materials that do not conduct electricity are called insulators.

4) Plastic materials, wood, rubber, leather, glass and cloth are insulators.

                               
                                      The material covering the wires is an insulator.
                                      Electricity cannot flow through it.



Conductors and Insulators Of Heat

1) Metals are also good heat conductors.

2) A good conductor of heat is also a good conductor of electricity.

3) Materials that do not conduct heat are called heat insulators.

4) Plastic materials, wood, glass, laether, rubber and cloth are also good
    heat insulators.

                       Cooking utensils and electric appliances are made from
                       metals such as iron and steel because they are good
                       heat conductors.
  

                                Handles of woks and ladles are made from plastic
                                or wood because they are good heat insulators. Users
                                can then hold the utensils without being burned.

4.3 Properties Of Materials

1) Different materials have different properties or characteristics as follows:

• conduct electricity
• conduct heat
• float in water
• absorb water
• can be stretched
• allow light to pass through

2) Materials that conduct electicity
    (a) A material that allows electricity to pass through it conducts electricity.
    (b) Objects made of metals, such as copper, iron and steel, can conduct
         electricty. Wires are made of copper (a metal) which can conduct electricity.
    (c) Carbon is a non-metal that can conduct electricity. Other non-metals
          cannot conduct electricity.

3) Materials that conduct heat
    (a) Materials that allow heat to flow from one part of an object to another
         conduct heat.
    (b) Objects made of metals can conduct heat easily. Metals such as steel and
          aluminium are used as cooking utensils to conduct heat quickly.
    (c) Non-metals, such as wood, rubber, leather, glass and plastic, do not conduct
        heat and electricity.
    (d) Materials that conduct heat can also conduct electricity.

The bulbs light up because the wires conduct electricity.

 

The pan conducts heat to the food quickly.

 

 

 

4) Materials that float in water
    (a) Objects that are made of wood and plastic can float in water.
    (b) They do not sink when put in water.
    (c) Objects made of glass, metal, cloth and clay sink in water.

Objects that float or
sink in water.



5) Materials that absorb water
    (a) Materials such as wood and cloth absorb water.
    (b) Objects such as a tissue and a towel become wet when they come
         into contact with water. These objects can be used to wipe wet surfaces.
    (c) Objects made of glass, metal, clay, rubber and plastic cannot absorb water.
         Water droplets can be seen on their surfaces when they come into contact
         with water.
    (d) Materials that do not absorb water are used to make waterproof objects
          such as umbrelas, raincoats and tents. These objects stop us from getting
          wet.

6) Materials that can be stretched
    (a) Objects made of rubber can be pulled and stretched.
    (b) These objects retutn to its original shape and size when released. They are
          elastic.
    (c) Examples of objects that can be stretched are rubber bands and springs.

A rubber band can be stretched.










7) Materials that allow light to pass through
    (a) Glass and certain types of plastics allow light to pass through them. An
          object can be seen if placed behind such materials.
    (b) Wood, metal and rubber do not allow light to pass through them. Objects
          cannot be seen if placed behind them.

4.2 Classification Of Materials

1) Some objects are made of one type of material. For example, a towel is made from cloth.

2) Some objects are made of more than one material.

3) An object can be made from different materials. For example, a mug can be made of glass, clay, plastic or stainless steel.

4) A material can be used to make different objects. For example, plastic can be used to make waste-paper baskets, containers, pencil boxes and cup.


Test Youself

Fill in the blanks with the correct words.

rubber	materials	metals
variety	wood	glass

1) We uses a _____________ of materials to make many types of objects.

2) Objects can be made from rubber, plastic, metal, _____________ or _____________.

3) Objects can be grouped according to the ____________ they are mede of.

4) Nails, needles, screws and knives are objects that are made of ____________.

5) Erasers, car tyres and balloons are objects that are made of ___________.

4.1 Materials Around Us

1) There is a great variety of materials around us.

2) The following materials can be used to make different objects.
_____________________________________________________________________

Wood

 Objects: furniture, blackboard, boat, ruler, pencil, paper, book.
____________________________________________________________________

Metal
 

Objects: spoon, knife, scissors, nail, ring, necklace, pot, pan, coin, tin.
________________________________________________________________________

Glass

Objects: jug, glass, mirror, window pane, bottle.
________________________________________________________________________

Rubber

Objects: eraser, hose, gloves, boots, tyre, ball, balloon, rubber band.
_________________________________________________________________________

Cloth

Objects: curtain, towel, clothes, handkerchief.
________________________________________________________________________

Leather

 Objects: belt, hat, shoes, wallet, handbag.
________________________________________________________________________

 Plastic

 Objects: ruler, bottle, containers, waste-paper basket, toothbrush, comb.
________________________________________________________________________

 Clay

 Objects: vase, ceramic tile, brick, bowl, plate, flower pot.
_______________________________________________________________________

 

Video - Mimosa Plants

3.3 Natural Defense in Plants

1) Plants have specific characteristics to protect themselves from being eaten or damaged by their predators.

2) The predators of plants are humans and animals.

Folding leaflets

1) Mimosa plants fold their leaflets when touched. The thorns are exposed.

                                                                     Mimosa

Latex

1) Papaya trees, jackfruit trees, yam plants and rubber trees produce latex in their stems, leaves and fruits.

2) The latex can cause itchiness which keeps away animals which eat them.

                                                         Rubber tree                                        Yam plant


Thorns

1)The fruit, stems and leaves of certain plants are covered with sharp thorns.

2) The thorns can hurt animals which try to eat or destroy the plants.

3) Examples: bougainvillaea, rose, cactus, pineapple, aloe vera, mimosa.

                                                Cactus                                                          Rose
 
Poisonous substances

1) The sap and fruit of the pong-pong tree are poisonous to humans and animals.

2) Some types of mushrooms are poisonous.

                                                                      Mushroom


Fine hairs

1) The stems and leaves of bamboo, sugar cane and pumpkins are covered with the fine hairs.

2) The fine hairs cause itchiness to animals which come into contact with them.

                                   Pumpkins                                                                       Bamboo trees
 

3.2 Living In Extreme Climates

1) Animals live in various habitats on Earth. Some habitats are very hot while others are very cold.

2) In order to survive, animals living in very hot or cold regions need to protect themselves from extreme climates.

3) Animals develop specific characteristics and behaviours that enable them to live in very hot or cold habitats.

Adaptations of animals to very hot climate

1) Animals like the elephants, hippopotamuses, rhinoceroses and buffaloes lose body heat through their wrinkled skins. The wrinkled skins have a bigger surface area, so more heat can escape from the bodies and help to cool their bodies on hot days. These animals also keep their bodies cool by wallowing in mud holes.

                              Hippopotamus                                                         Buffalo


2) Camels are able to survive in extremely hot deserts. Camels have long eyelashes and ear hairs to prevent sand from entering their bodies. Camel store food and water in the form of fats in the humps on their back. This adaptation allows them to go for days without food and water.

                                                                           Camel
 3) During the day, most desert animals are not active. They hide under rocks and in holes to keep away from the heat.



Adaptations of animals to very cold climate

1) In cold regions, most animals have thick fur and layers of fat under their skins.

2) Polar bears have thick fur to prevent the body from losing heat to the cold surroundings.

                                                                         Polar bear
3) Polar bears, penguins, walruses, seals and whales have layers of fats under their skin to keep their bodies warm.

                                             Whale                                                                        Penguin


4) Seals and walruses have small ears to prevent heat loss from their bodies.

                                    Walrus                                                                                     Seal