Clasification of materials
There are many ways to classify materials, one of them is to classify them as raw materials and processed materials.
Raw materials are those materials that exist in nature and which we use as they are: wood and stone, for example.
Processed materials. We transform them to make a different material with better properties.
For example, we extract iron ore from mines, but we transform it into steel before use it.
So iron ore is a raw material.
Steel is a strong material. It is good for making things.
So steel is a processed material.
Elasticity: is the ability of a material to change its shape when a force is applied to it and to recover its original shape when the force disappears.
Ductility: is the ability of a material to be stretched into a new shape when a pulling force is applied to it and then to keep the new shape when that force is removed.
MECHANICAL PROPERTIES
Elasticity: is the ability of a material to change its shape when a force is applied to it and to recover its original shape when the force disappears.
Example: rubber.
Malleability: is the ability of a material to be squeezed or hammered into a new shape when a compression force is applied to it and to keep the new shape when the force stops. Metals are malleable. This property is useful for making sheets.
Ductility: is the ability of a material to be stretched into a new shape when a pulling force is applied to it and then to keep the new shape when that force is removed.
This property is useful for making wires.
Hardness: is the capacity to scratch other materials. Hard materials scratch softer materials. For example, diamonds are harder than glass, so you can scratch glass with a diamond.
Toughness: can be defined as the resistance to breaking of a material.
It is difficult to break objects that have been made of tough materials, even if they suffer repeated impacts.
Electrical conductivity: Is the ability of a material to let electrons
flow (electric current) through a material. Sometimes we want the electricity to flow easily, so we use conducting materials (example. copper), sometimes we do not want the electricity to flow, so we use insulating materials (example: plastics)
Thermal conductivity is the ability to let heat flow through a material.
Extrudability. Extrusion is the action of pushing a material through a hole with the desired shape.
The damage caused depends on the toxicity of the substance and on the dose. We must consider not only the toxicity in humans but also the possible toxicity in the soil, water or air.
Activity 3:
PHYSICAL PROPERTIES
Density: is the combination of weight and volume. It can be expressed with the following equation:
(watch out for units, usually we use Kg/l or g/cm3)
ELECTRICAL PROPERTIES
Electrical conductivity: Is the ability of a material to let electrons flow (electric current) through a material. Sometimes we want the electricity to flow easily, so we use conducting materials (example. copper), sometimes we do not want the electricity to flow, so we use insulating materials (example: plastics)
THERMAL PROPERTIES
Thermal conductivity is the ability to let heat flow through a material.
Heat flows easily through metals, but not through wood, ceramic or plastic. We can speak about thermal conductor and thermal insulator materials.
TECHNOLOGICAL PROPERTIES
Mouldability is the ability of a material to fill a mould.
We heat metals until they are liquid and then we pour them in the mould. When the metal cools down, it becomes solid and we can take the piece from the mould.
Extrudability. Extrusion is the action of pushing a material through a hole with the desired shape.
A good example is toothpaste. When you squeeze the tube you extrude the paste through the hole.
Aluminium bars and tubes are easily manufactured by extrusion.
ECOLOGICAL PROPERTIES
Toxicity is the capacity of a substance to damage an organism by ingestion,
inhalation or skin contact.
The damage caused depends on the toxicity of the substance and on the dose. We must consider not only the toxicity in humans but also the possible toxicity in the soil, water or air.
It is important to use non-toxic materials when the object will be in contact with people, or with food or water consumed by people.
Some substances are not toxic but damage the environment. For example, carbon dioxide produces the greenhouse effect,
but is not toxic if you breathe it.
Recyclability is the capacity of a material to be recycled.
It is not really a property of the material itself. It depends on the way the material is used in the object, the recycling technology available and the way in which the user disposes of the object.
ACTIVITIES
Activity 1:
Go to http://www.bbc.co.uk/schools/ks2bitesize/science/materials.shtml and click on the "Characteristics of materials'' activity. Follow the instructions to do the activity.
Then click on "Revision Bite'' and click again on "Material properties. Copy into your notebook the definitions of transparent, opaque, waterproof, strong, flexible, hard, magnetic and conductor.
Go back to the first page and click on "Quiz''. Complete the quiz. Good luck!
Activity 2:
Complete the table below by marking the properties that best describe the material.
| Strong | Weak | Light | Heavy | |
| Paper | ||||
| Cardboard | ||||
| Cork | ||||
| Wood | ||||
| Plastic | ||||
| Metal | ||||
| Knitting wool |
Activity 3:
Some materials (wood, for example) have different mechanical properties depending upon the direction of the force. This is because they have fibbers inside that are aligned in a particular direction.
Cut two identical pieces of wood (dimensions: 5 mm x 10 mm x 50 mm).
Piece "A" with the fibres across the piece and piece "B" with the fibres along the length of the piece.
Test them to see which one breaks more easily.
Explain if you think that the fibres are stronger than the material that bonds them or if you think that the bonding material is stronger than the fibres.
