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.
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.
(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.
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.
(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.
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.
2. Copper, silver and bronze are used to make coins and medals. Copper is used to make electric wires and water pipes.
3. Gold and silver are used to make jewellery and other decorative items.
4. Tin is used to make cans and tin lamps.
5. Aluminum is used to make saucepans.
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.
2. Galvanisation This is the process of applying a protective zinc coating to iron.
The zinc coating protects the iron surface from rusting.
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;
Example: A metallic block has a mass of 500g and a volume of 50cm3. Calculate the density of the block.
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.
(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) 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) 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.
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.
(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:
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:
Example The density of kerosene is 0.8g/cm3. If the density of water is 1g cm3, calculate the relative density of
kerosene.
Relative density is measured using a hydrometer. The following pictures show a hydrometer and how it is used.
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.
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 objectsWhat 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.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 waterRelative 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?(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 referenceto 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 textbookGlossary 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