Category : 6th Class
1. To learn about materials that are used for making objects
2. To understand grouping and sorting of materials
3. To learn about classification and its importance
4. To understand different properties of materials such as appearance .roughness .hardness, solubility, transparency, flotation, magnetic and conduction property
We have a number of objects around us like trees, toys, paper, table, chair etc.
Some of these objects are living and some are non-living. Non-living objects can be man-made or natural. Objects around us may have different size, shapes, colours and uses. All objects around us are made up of one or more type of materials such as paper, glass, plastic, cloth, wood, metal, mud, soil, cotton, etc.
An object can be made from different materials. For example, chair can be made from wood or plastic.
Different objects can be made from the same material. For example window panes and fish bowl are made from same material, glass.
Several objects are made up of combination of several materials. For example mango shake is made up of mango, milk, sugar etc.
Different materials have different properties. Many objects differing in usage can be made from the same material. There are so many ways to group objects.
Placing similar things together is called grouping-For example in supermarket grouping is done by keeping similar items on same shelf, which make it easier for us to find the item we need.
The process of sorting and grouping objects/things according to some basis is called Classification. It makes study of large number of objects of different type easier, simple, systematic and convenient.
PROPERTIES OF MATERIALS
Different types of materials have different properties. Some of the important properties of materials are given as following.
In appearance materials usually look very different from each other. The appearance of wood is different from iron. Similarly appearance of iron is different from copper or aluminum.
Some materials when freshly cut appear shiny where as others have no shine Metals shine in their pure state. This shining property of metal is called metallicIustre.
Some materials having lustre are iron, copper, aluminum, gold, silver, etc.
Materials can be classified on the basis of their luster as lustrous materials, for example gold, silver etc and non-lustrous materials for example wood, plastic, stone etc.
Shining property of gold, copper and silver is used for making jewelry. Some metals often loose their shine when exposed to air and moisture for some time.
Hardness: On the basis of hardness materials can be classified as soft or hard.
Soft materials are those which can be easily compressed or scratched e.g. cotton, sponge
Hard materials are those which are difficult to compress e.g. iron, stone, wood, diamond, etc.
We can identify soft or hard materials by pressing different materials with our hand. Hard materials cannot be compressed easily while soft materials can be easily compressed.
Talc that is used for making talcum powder is a very soft substance.
Wood and diamond are examples of hard substance.
Do You Know
Diamond is the hardest natural substance.
Materials can be rough or soft. If a material has bumps or ridges on its surface which can be felt by touching them, such materials are said to be rough For example rocks, bark of a tree, brick etc are rough materials. Smooth materials do not have bumps. For example window pane, cup, plates, mirror etc.
An important property of water is its ability to dissolve many substance in it.
Many of the solid liquid and gases dissolve in water.
Solubility of solids in water: Some of the solid substances dissolve when placed in a container containing water and stirred where as some remainundis solved.
The solid substances that dissolve in water are called soluble substances e.g. salt, sugar etc.
The solid substances that remain undisclosed are called insoluble substances. e.g. sand, saw dust etc.
Water can dissolve a large number of substances and plays an important role in functioning of our body.
Solubility of liquids in water : When liquids are mixed with water, Some get completely mixed and are known as miscible e.g. vinegar, lemon juice Some do not mix and form a separate layer and are known as immiscible substances e.g. mustard oil, coconut oil, kerosene etc.
Solubility of gases in water: Some gases are soluble in water e.g. hydrogen chloride gas, carbon dioxide gas, ammonia gas etc. Some gases are in soluble in water e.g. nitrogen, hydrogen etc. Water, usually, has small quantities of some gases dissolved in it e.g. oxygen dissolved in water is very important for the survival of animals and plants that live in water.
Lemonade and other carbonated drinks are examples of gas dissolving in water as these drinks contain carbon dioxide gas dissolved in water.
Do You Know
Animals living in water breathe the oxygen dissolved in water. Water plants use the carbon dioxide dissolved in water for photo synthesis.
Some materials when dropped in water float on its surface e.g. dried leaves, dry wood, feather etc.
Some materials when dropped in water sink in water e.g. stone, iron nail etc.
The concept of flotation following or sink can be understand by taking following example.
When a stone is placed in water, the water level rises. In this case, water is said to be displaced (moved somewhere else) by the stone. If the weight of this displaced water is greater than the weight of the stone, the stone will float otherwise it will sink.
Do You Know
Archimedes, a Greek physicist of the third century BC, discovered the principle of flotation known as Archimedes principle. According to the principle, when a body is wholly or partially immersed in a fluid there is an up thrust which is equal to the weight of fluid displaced.
The shape of an object also affects the amount of liquid it would displace.
Certain heavy objects are also able to float because of their shape. For example the shape of a ship allows it to float on water, despite the fact that it is very heavy.
On the basis of transparency the objects can be divided as follows:
Transparent objects are those objects through which things can be seen (i.e. they allow the light to pass through them) e.g. glass, water, air, some plastics etc.
Shopkeeper mostly keep sweets .biscuits etc. in transparent container so that customer can select item of his choice.
Air is transparent that is why we are able to see things around us, even though air is all around us .Clean water is also transparent.
Opaque objects are those objects through which you are not able to see (i.e. they do not allow the light to pass through them) e.g. metals, cardboard, wood etc.
Translucent materials are those materials through which objects can be seen but not clearly e.g. oiled paper.
SOME OTHER PROPERTIES OF MATERIALS
Materials that are attracted to a magnet are called magnetic materials. For example iron and steel are magnetic material. Nickel and cobalt are also attracted to wards magnet. Aluminum, gold, wood, plastic etc. are not attracted to wards magnet these are called non-magnetic materials.
Magnetic property of iron is used in doors of admirals and refrigerators and various electronic devices.
Conduction of Heat
Utensil kept in kitchen are usually made up of metals and their handles are made up of plastic or wood. This is because metals get heated where as materials such as wood and plastic do not.
Materials that allow heat to flow through them are called good conductors of heat, for example metals whereas those that do not allow heat to flow through them are bad conductors of heat. For example paper, wood, plastic and glass are bad conductor of heat.
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