• UNIT 16: MATERIALS

    Introduction

    Materials refer to things around us. These things can be solids, liquids or gases. 

    We use materials around us in our daily activities.

    Look at the following pictures.

    B

    Describe each picture above.

    Use the pictures to predict what you are going to learn.

    16.1:  Classification of materials

    Natural materials can be classified broadly into two:

    1. Metals    

    2.  Non Metals

    Activity 16.1: Grouping materials as metals and non-metals

    What to do:

    (i) Identify various materials used at home and at school:

    • Bell   

    •  Hoe    

    •  Thread  

    •  Glass

    • A nail   

    •  saucepan   

    •  Spoon     

    •  Book

    •  Brick   

    •  Plastic pens  

    •  Piece of iron sheet   

    (ii) Make a table like the one shown below in your notebooks.

    t

    (iii) Group the materials collected as metals or non metals.

    (iv) Give reasons for grouping the materials as you did.

    (v) (a)   Do the following to the materials: 

      •  Hit them with a stick.       

    •  Feel how heavy they are.  

     •  Observe their appearance.   

    •  Bend and straighten them.  

     •  Stretch them.

     (b)  Write down general characteristics  of metals and non metals  from your observation in (a) above.

    (vi) Compare how you grouped the materials and the observations that you have made.

    Non metals

    A non metal is a material that lacks metallic characteristics. The following are major properties of non metals:

    1. Most non metals are poor conductors of both heat and electricity.

    2. They are soft and break easily.

    3.  Most have a dull appearance.

    Write in your notebooks two other properties of non metals.

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    Common examples of non metals include bricks, paper, plastics, wood and glass.

    Metals

    A metal is a material that is typically hard and shiny. 

    Common metals

    In nature, metals are found on or in the earth crust. 

    Examples of common metals include aluminum, zinc, iron, tin, lead, copper, silver and gold.

    Physical properties of metals

    Activity 16.2: investigating physical properties of metals

    What you need:

    • Heat source  

    •  Nail  

    •  Wooden handle or piece of cloth What to do:

    (i) Light the heat source.

    (ii) Heat the nail gently.

    (iii)  What can you feel?

     Caution: Do no hold the nail until it is very hot or you will get burnt.

    (iv) Use a wooden handle or piece of cloth to hold the nail. Now heat the nail.

    X

    (v) What do you feel? Why?

    observation

    • When you hold the nail in your hand and heat it, it will get hot. You will feel the heat in your hands. • When you hold the nail with a wooden handle or a piece of cloth, you will not feel the heat. 

    The wooden handle or piece of cloth is not a good conductor of heat.

    Conclusion

    Metals conduct heat.

    The following are the general physical properties of metals:

    1. They are shiny.

    2. They are sonorous – Most make a bell-like sound when hit. 3. They are good conductors of electricity and heat.

    Name 5 other properties of metals.

    C

    16.2: uses of common metals

    Activity 16.3: identifying uses of common metals

    (i) Collect metallic materials such as cans, nails, coins, spoons, axe, electric wires, iron sheet pieces 

    and bring them to school.

    (ii) Group them according to the metal they are made from.

     1.  Iron is used to make roofing materials hoes, shovels, screws and nails.

    K

    2. Copper, silver and bronze are used to make coins and medals. Copper is used to make electric wires and water pipes.

    D

    3. Gold and silver are used to make jewellery and other decorative items.


     B

    4.  Tin is used to make cans and  tin lamps.

    Z

    5. Aluminum is used to make saucepans.

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    Fig. 16.3: Common objects made of metals.

    Practice Activity 16.1:

    Using your XO Browse Activity:

    1. Search and write in your notebook other uses of metals. 2. Find out what metal a 50 Rwandan Franc coin is made of. 3. Search and write in your notebook metals that are found in Rwanda or the neighbouring counties.

    16.3: Maintenance of metals

    Activity 16.4: identifying maintenance of metals

    (i) Go for a walk around your school.

    (ii) Observe the roofs.

    (iii)  Comment about roofs that are painted and those not painted. (iv) Discuss why metallic tools are maintained by oiling and storing in a dry place.

    1. Painting the metal 

    Painting metals prevents corrosion. Corrosion occurs when moisture and air react with a metal. 

    Painting keeps the metal surface free from air and moisture. 

    Z

    2. Galvanisation This is the process of applying a protective zinc coating to iron.

     The zinc coating protects the iron surface from rusting.


    V

    3.  Store in a dry place: All metallic tools and equipment need to be stored in a dry safe place.

     4. oiling: Moving or rotating metallic parts should be oiled to reduce friction. 

    16.4: Density

    Activity 16.5: Defining density

    (i) Using your XO laptop research for the definition of density.

    (ii) Write down the definition in your notebook. Density is defined as the mass of a substance per unit volume.

    Calculation of density Density of a substance is obtained when you divide the mass of that substance by its volume. It is expressed mathematically as;

    F

    Example: A metallic block has a mass of 500g and a volume of 50cm3. Calculate the density of the block.

    D

    The standard unit used in measuring density is grams per cubic centimetre (g/cm3). The other unit is kilograms per cubic metre (kg/m3).

    Activity 16.6: Measuring density of materials

    (a) Measuring the mass of the materials

    It is measured using a beam balance or weighing scale. Materials needed:

    •  Wood  

      •  Water in a container 

    •  Weighing balance

    •  Nails   

    •  Stone      

    •  Metallic hammer or knob

    What to do:

    (i) Use a weighing balance to measure the mass of water and nails as shown below.

    C

    (ii)Use the same weighing balance to measure the mass of wood, nails, stones and 

    metallic hammer or knob.

    (iii) Record their mass in a table like the one shown below.

    B

    (b) Measuring the volume of irregular materials Volume of regular objects like cubes and rectangles is calculated using formulae. Volume of irregular objects is obtained using the displacement method.

    Materials needed:

    •  Water in a container      

    •  Wood     

    •  Thread      

    •  Metallic hammer or knob   

    •  Stone  

    •  Nails 

    •  Measuring cylinder or container with volume markings.   

    What to do:

    (i) Collect water in a measuring cylinder or marked container. 

    (ii) Note the initial level of water in the cylinder. Record it as initial volume of water.

    (iii) Tie a piece of thread around a stone.

    (iv) Lower the stone gently into the measuring cylinder or container. What happens?

    V

    (v) Note the final level of water. Record it as final volume of water.

    (vi) Find the volume of the stone as follows: 

    Volume of material  =  Final volume of water – Initial volume of water

    (vii) Put the other objects one at a time into the measuring cylinder with water.

    (viii) Measure the initial and final volumes of other objects and record them in a table as shown below.

    G

     Question Calculate the volume of the stone used in this experiment.

    (c) Calculating density

    (i) Record the mass and density of the measurements in (a) and (b) in a table as shown below.

    X

    (ii)  Compare the mass with the volume of the different materials.

    (iii)  Calculate the ratio between measured mass and volume of each of the objects.

     Use the formula:  C

    Relative density

    This is the ratio of the density of a substance to the density of a given reference material. Normally, the reference material is the density of pure water.

    The formula for calculating relative density is: 

    B

    Example The density of kerosene is 0.8g/cm3. If the density of water is 1g cm3, calculate the relative density of 

    kerosene.

    K

    Relative density is measured using a hydrometer. The following pictures show a hydrometer and how it is used.

    B
     z

    Fig.16.5:    A hydrometer and how it is used.

    Activity 16.7:  Measuring densities of liquids using a hydrometer

    What to do:

    1.  Using a hydrometer, measure the density of liquids such as clean water,unclean water,cooking oil,    paraffin,juice, milk, salty water among others.

    2.  Record your finding in a table as shown below.

    j

    3.  Compare different values of densities of measured objects with the density of water.

    Application of relative density

    Some  objects have a  lower density compared to water. While some objects have a higher density    compared to water. This relative density (high or low)  of objects determine their behaviour on water.

    Activity 16.8: Experiment on behaviour of different objects in water and relative density

    Materials needed:
    • Water                                • Saucepan
    • Basin or sink                     • A bottle (with lid) full of water
    • Paraffin                             • An empty bottle with lid (full of air)
    • Stone                                • Feather
    • Cooking oil                        • Metallic hammer
    • Metallic spoons                 • Plastic objects

    What to do:
    (i) Put water in a basin or sink (up to ¾).
    (ii) Gently put the objects listed above in water one at a time.

    g


    Observe how the objects behave. Compare their behaviour in water.
    (iii) Which objects sink in water? Record them in your notebook.
    (iv) Which objects float on water? Record them in your notebook.
    (v) What conclusion can you make concerning relative density of objects and their ability to float or sink?
    Conclusion
    Objects that have a lower density than water float on water. Objects that have a higher density than water sink in water

    Relative density is applied in our everyday lives as follows:
    1. It is applied during designing of structures like ships and planes.
    • A ship has to be hollow that it can float. Making the ship hollow reduces its density.
    • Materials used for building the parts of aeroplanes should have a low density.

    A good example of such material is aluminum.
    2. Relative density is used to determine the purity of some substances.

    For example a lactometer is used to measure density of milk to find out if it is pure or water has been added.
    3. The knowledge of relative density is applied to determine the mineral content in a rock.

    4. Density is also considered during the design of swimming and diving equipment.

    Revision Activity 16

    1. Materials can be classified into two broad groups. Name them.
    2. Name three properties of non metals.
    3. What type of metals are the following things made of?
    (a) Spoon

    (b) Rwandan 100 franc coin
    (c) Electric wires

    (d) Iron sheets
    (e) Diamond necklace
    4. Outline 3 physical properties of metals that you can test in class.
    5. Describe briefly how you can measure the volume of an irregular metallic ring.
    6. (a) Give the general formula for calculating density.
        (b) Calculate the density of a stone that has a mass of 1 000 kg and volume of 50 m3.
    7. The density of a piece of wood is 12 g/cm3, the volume is 10 m3. Calculate the mass of the wood.
    8. A metallic knob was put in a measuring cylinder containing water. The water rose from 63 cm3 to 85 cm3. Calculate the volume of the stone.
    9. (a) What is the instrument shown below used for?

    s

         (b) What is the standard unit used in the instrument shown above?
    10. (a) A feather floats on water but a pin sinks in water. Explain this behaviour of objects with reference   

          to their densities.

          (b) Describe briefly 2 applications of density that use the behaviour explained in (a) above?
    11. (a) What is galvanising.
          (b) A farmer has roofed his cowshed with new iron sheets. Advise him on how he can maintain the roof.

    Word list
    1. Read the following words in pairs.
    • Conductors                      • Malleable                       • Electricity
    • Galvanization                   • Aluminium                     • Density
    • Mass                                • Measuring cylinder        • Volume
    • Hydrometer                      • Weighing balance         • Relative density
    2. Spell 3 words while your friend writes them in his or her notebook. Let your friend also spell 3 other words as you write them in your notebook.
    3. Discuss with your friend the meaning of any 3 words in the word list.
    Refer to notes in your textbook

                                               Glossary and Index

    Absorption of food      Uptake of digested food into the body

    Afforestation                  Planting of trees where they did not exist

    Agroforestry                   Practice of growing crops together with trees

    Ant-erosive plants         Also known as cover crops. Plants that grow and cover the soil surface e.g
    pumpkins, sweet potatoes e.t.c.

    Abstinence                       Not having sex before marriage

    Boluses                            Small portions of food rolled into balls by the tongue in the mouth

    Compound fertilisers        Fertilisers that contain two or more major nutrients

    Cash crops                           Crops grown for sale

    Chlorination                         Purifying water using chemicals (Chlorine) to kill germs

    Condensation                       Change of gas/vapour into liquid

    Data                                       Facts and figures that are processed by the computer

    Deficiency diseases             Diseases caused by lack of certain food nutrients in the body

    Deforestation                        Cutting down trees

    Density                                    Mass of a substance per unit volume

    Digestion                                Process in which food is broken down into smaller particles

    Duodenum                             Upper part of the ileum in the digestive system

    Egestion                                 Removal of the undigested food through the anus

    Evaporation                             Change of liquids to gases

    Food crop                                Crops that are grown for human food

    Galvanisation                           Process of coating iron metal with zinc to protect it from rust

    Genitals                                    Reproductive organs

    Hard disk/Hard drive                  Primary storage device found in computers

    Herbal medicine                         Medicine got from plants

    Incubation/Brooding                    Keeping eggs under conditions that allow them to hatch into chicks

    Incubator                                    Special machine that allows the eggs to hatch

    Inbox                                           Computer folder in which newly delivered e-mail messages appear

    Infatuation                                   A strong but often short-lived liking for another person

    Ingestion                                       Uptake of food into the mouth

    Kickback                                        Pieces of wood thrown back when using a saw

    Leaching                                     Process in which nutrients in soil are dissolved and drained deep in the  

                                                         soil  by water

    Masonry tools                             Tools used in the construction of farm structures and buildings

    Menstruation                               Shedding blood through the vagina in adult females after every 28 days

    Opaque                                        Materials that do not allow light to pass through them

    Ornamental trees                          Trees that beautify a place

    Parasite                                        An organism which lives in or on another living organism (host) deriving nutrients from it

    Peers                                            Boys or girls of the similar age group

    Photosynthesis                             Process in which green plants make their own food

    Precipitation                             When water droplets condense to form clouds in the sky and then fall down to the earth as rain, snow, etc. Rain and snow are examples of precipitation.

    Premarital                                  Before marriage

    Puberty                                       Period where a boy or girl reaches sexual maturity

    Reflection                                     Bouncing back of light when it falls on a smooth shiny surface

    Refraction                        Bending of light rays when they travels from one transparent medium to another

    Relative density               Ratio of the density of a substance to the density of a given reference material

    Resizing                              Making an image bigger or smaller

    Rhombus                              A figure that has four equal slanted sides

    ROM                                      Read only memory: Permanent storage memory in computers

    RAM                                      Random Access memory: Temporary storage memory in computers

    Sanitation                             Cleanliness of the body and the surroundings

    Seed bed                                An area of land/soil prepared for planting seeds

    Sprites                                    Objects that perform actions in scratch dialogues or cartoons

    Straight fertilisers                    Fertilisers that contain only one major nutrient

    Tool                                            Hand held device used to carry out a particular function

    Transpiration                                 Loss of water in plants through the stomata

    Translucent                                   Materials that allow some light to pass through them

    Transparent                                   Materials that allow all the light to pass through them

    Trapezium                                       A four sided figure that has two parallel sides

    Voice breaking                                Voice becoming deeper in boys undergoing puberty

    Waterborne diseases                        Diseases transmitted through contaminated water

    Water pollution                                  Introduction of harmful substances in water

    Wet dreams                                        Discharge of semen by adolescent/ young males during sleep

    UNIT 15:ELECTRICITYUnit17:SET MODEL QUESTIONS