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UPSR Sains 2012 Ep 17

Keadaan Bahan Muat Turun

    • Different objects are made of different materials. Examples:
      • Clay – brick, porcelain vase, ceramic sink
      • Rubber – ball, tyre, rubber gloves
      • Silk – necktie, dress, scarf
      • Glass – bottle, mirror, window pane
    • Different materials have different properties. Examples:
      • Cotton and paper can absorb water
      • Rubber can be stretched
      • Wood and most plastics float on water
      • Clay, metal, paper and rubber sink in water
      • Metal can conduct electricity and heat
      • Plastics, rubber and wood does not conduct electricity and heat
    • An object that allows all light to pass through it is said to be transparent.
    • An object that allows some light to pass through it is said to be translucent
    • An opaque object does not allow any light to pass through it.
    • The material chosen to make to object depends on the properties of material. Example:

      Object Required properties of material Suitable material
      Clothes Absorbs sweat, soft Cotton cloth
      Medical glove Can be stretched, waterproof Rubber
      Sampan Floats on water Wood

    • All material can be divided into two big group:
      • Natural materials: clay, cotton, glass, leather, metal, paper, wool, wood
      • Man-made materials: plastics, synthetic cloth
    • Some natural materials are renewable but some are not. So, we need to conserve materials by reusing, reducing and recycling.
    • Reusing means to use unused or waste materials again, either for the same or different purpose.
    • Reducing means use less amounts of materials than usual.
    • Recycling means reprocessing unused or waste materials into useful new products.
    • Objects made of iron or steel can rust.
    • Two factors that cause rusting are air and water.
    • If any one of these two factors is absent, then rusting cannot take place.
    • Rusting can be prevented by keeping objects made of iron or steel away from air and water. Example: applying grease or oil to the surface of an iron or steel object prevents air and water (moisture) from reaching the surface.