Why we use these materials?
CLASSIFICATION OF MATERIALS
WHAT IS CLASSIFICATION?
Grouping of objects into sets according to one or more common properties.
HOW DO WE CLASSIFY?
Classified using their properties (similarities/differences)
-
colour
- flexibility
- hardness
- strength
- degree of transparency to light
- magnetic property
- thermal property
- electrical property
- density
- boiling point & melting point
- malleable (can change shape without breaking)
- ductile (capable of being hammered out thin)
WHY CLASSIFY?
-
Get the things organized to find them easily ← It allows you to see things in an orderly way.
- Easier to study
To show similarities and differences among different things ← You cannot study everything around you. So, by knowing the group, you’ll get to know the characteristics
- Can determine the uses of materials by knowing their properties
- We can make new materials to have the properties we want
When you choose a material to make an object, you need to know:
- the properties of the material
- the uses of the object
Classifying the material according to their properties helps us to choose suitable materials for making objects.
(An object can be classified into more than one class according to the way of classification)
Objects(materials ) are often recognized by their physical properties.
Physical property = a characteristic of matter that can be observed without causing any damage to the matter.
There is more than one way to classify the SAME set of objects
5 main classes of materials:
- Metals
- Glass
- Ceramics
- Plastics
- Fibres
SOME PHYSICAL PROPERTIES, USED FOR CLASSIFICATION:
- Def – Amount of mass in each unit volume of the material
- Each substance has its own density. (D = M/V)
- Can find the density of a piece of jewel & compare with the density of the
real gold → Can find if the jewel is made of real gold (or pure gold)
- Inspectors can check the density of the milk to find if it has been diluted.
- Def – Ability to support a heavy load without breaking or tearing
-
Steel & concrete are strong materials → used for building purposes.
- Metals:
- Most pure metals are weak (eg: Iron)
-
So, they are mixed with other metals or non metals to make more stronger (eg: Iron + Carbon → Steel).
- Steel is stronger than iron
-
Mercury is a pure metal that is stronger than steel → used for making crowns for the broken teeth (dental filling)
Experiment to test STRENGTH:
- Hang different weights & find out which weight breaks each material.
- Stronger materials need higher weight to break them
- (Weight of the material ITSELF doesn’t determine the strength of it)
- Def – Ability of a material to withstand scratches and wear
-
Scratching method is used to test the hardness → a harder material can
scratch a softer material.
-
Diamond (a form of carbon) is extremely hard → can only be cut by other diamonds
- Graphite (another form of carbon) is softer
-
Titanium (a metal) is one of the hardest metals → used for the construction of aircraft & artificial human bones
Mohs’ scale of hardness:
- Created by Friedrich Mohs (a Germonminerologist)
- A scale from 1 to 10 (based on ten minerals)
- The higher the number, the harder the mineral
Diomond = 10
Corundum = 9
Topaz = 8
Quartz = 7
Orthoclase = 6
Apatite = 5
Fluorite =4
Calcite = 3
Gypsum = 2
Talc = 1
Experiment to test HARDNESS
- Hard materials are difficult to scratch.
-
If A makes a scratch mark on B (but B doesn’t make mark on A) → A is harder than B
Def – Ability to bend without breaking and return to its original shape
Least flexible = the material that needs the largest weight to bend
Test to compare flexibility:
(Pg 80 – Sec 1 txt bk)
Def – Ability to return to its original shape after being stretched
Def – A measure of how readily electricity glows through the material
-
Electrical conductors – allow electricity to pass through easily (eg: all metals & carbon)
-
Electrical insulators – doesn’t allow electricity to pass through easily (eg: all non-metals except carbon)
Def – A measure of huw readily heat flows through he material.
-
Good conductors of heat – allow heat to pass through easily (eg: metals)
-
Poor conductors of heat – doesn’t allow heat to pass through easily
- Def – This is the temperature at which a substance change from solid to
liquid
-
Melting point of pure ice = 00C
-
Melting point of iron is very high = 15390C
-
Melting point of gold is very high = 10630C
-
Melting point is also used to test the purity of the substance
- Def – This is the temperature at which a substance change from liquid to
gas
-
Boiling point of pure water = 1000C
- Boiling point of metals are very high
-
Lead = 17400C
-
Nickel = 2840 0C
-
When pressure is high → boiling point decreases → fast/easily cooked in pressure cooker
Def – the ability to a substance to dissolve in water
Solubility depends on the temperature of the water (Solubility increases with temperature)
Def – Ability of a liquid to flow (describes how easily or how difficult the liquid flows)
Def – Ability of a substance to aloow light to pass through it
- Transparent – Materials that allow most light to pass through (clearly see through)
- Translucent – Material that allow some light to pass through (cannot clearly see through)
- Opaque - Materials that do not allow light to pass through (cannot see through)
- Magnetic
- Non magnetic
SOME OTHER WAYS TO CLASSIFY MATERIALS
Classification 1 – Once alive & never alive
Classification 2 – Natural & Man-made
- Natural – crude oil, carbon, iron, copper, wood, rubber
- Man made (synthetic) – these are made from different natural material that are processed to produce new man-made materials
Eg: petrol & plastic (made from crude oil), glass, steel
Classification 3 – Metals & Non-metals
- Non metals – plastics, fibres, glass, ceremic
- Metals – iron titanium, aluminium, gold, zinc, copper, lead
Some experiments:
