Class 6 Science Chapter 6 Notes Materials Around Us
Grouping of Materials
Different objects are made up of different materials. The method of arranging the objects into groups is called classification. The classification is done to group the objects according to the materials they are made up of.
- The same object can be made up of different materials, e.g. plate can be made up of steel, glass, plastics, etc., similarly, toys can be made up of plastics, rubber, metal, etc.
- Different types of objects can be made up of the same material, e.g. leather, which can be used to make belts, wallets, purses, bags, etc. Similarly, we can classify materials based on the similarities and differences in their properties.
Different Properties of Materials
We choose materials for making an object based on the properties of materials and the purpose for which the object is to be used. For example, we make a tumbler from materials such as glass, plastic or steel because all these materials have the property of storing water or other liquids. But, we cannot make a tumbler from a piece of cloth because it cannot hold water. Similarly, it would not be a wise idea to use paper for cooking utensils. Now, here is how some of these properties help us pick the right material for each purpose.
Appearance
Some materials have a shiny appearance, while some materials might appear dull. For example, gold, silver, and iron appear shiny, while wood, plastic, paper, and rubber have a dull appearance. Materials that appear shiny are said to have luster (or in Hindi chamak) and thus, are called lustrous materials. Such materials with luster are usually metals. However, these metals often lose their shine and become dull when they are exposed to air and moisture. Their shine reappears when they are freshly cut or their surface is scratched.
Non-lustrous materials are those that do not have a shiny surface and have a dull appearance like paper, wood, rubber, chalk, plastic, and jute. It should be noted that not all the materials that shine need to be metals in the same way as all the glitters are not gold. The surface of some materials is made shiny by polishing or creating them with thin layers of plastic, wax, or any other materials that make them look shiny.
Hardness and Softness
Materials that are difficult to compress or scratch are called hard materials. For example, wood, steel, iron, stone, diamond, brick, glass, etc. Materials that can be compressed or scratched easily are called soft materials. For example, sponge, wool, cotton, rubber, butter, chalk, feather, jelly, clay, etc. The properties of hardness and softness are relative. For example, rubber is harder than sponge but softer than wood. Diamond is known as the hardest natural material.
Transparency
Based on the property of a material which tells whether we can see through it clearly or not, materials are classified into three types as follows.
(i) Transparent Materials:
Materials through which we can see are called transparent materials.
For example, glass, air, water, alcohol, cellophane paper, etc.
(ii) Translucent Materials:
Materials through which we cannot see are called translucent materials (or semi-transparent materials).
For example, butter paper, frosted glass, oiled paper, clouds, etc.
(iii) Opaque Materials:
Materials through which we cannot see at all are called opaque materials.
For example, cardboard, rocks, bricks, wood, stone, metals, notebooks, etc.
Clean water is also a transparent material. This can be understood as when we put any object (say a coin) in a glass filled with clean water, we can see the coin clearly at the bottom of the glass.
Solubility in Water
Solubility is defined as the ability of a solid, liquid, or gaseous substance to dissolve in a solvent (usually liquid). Materials are classified into two types based on solubility.
- Soluble materials in water: The materials that disappear when mixed in water, i.e. they dissolve in water, are called soluble materials.
- Insoluble materials in water: The materials that do not disappear when mixed in water, even if we stir them for a long time are called insoluble materials.
Solubility of Solid in Water
- Some solids completely dissolve or disappear in water and are soluble in water. For example, sugar, salt, milk, lemon juice, alcohol, copper sulphate, baking soda, washing soda, etc.
- Whereas, some solids do not completely dissolve or disappear in water and are insoluble in water. For example, sand, chalk powder, plastic, paper, wax, oil, petrol, glass, kerosene, wood, etc.
Solubility of Liquid in Water
Some liquids are soluble (miscible) in water as they dissolve in water and do not form a separate layer when mixed with water. For example, milk, lemon juice, glycerine, vinegar, alcohol, etc., whereas, some liquids are not soluble (immiscible) in water as they do not dissolve in water and form a separate layer when mixed with water. For example, petrol, coconut oil, groundnut oil, olive oil, kerosene, etc.
Solubility of Gases in Water
Some gases are soluble in water, while some gases are not. For example, oxygen gas dissolves in water and is very important for the survival of animals and plants that live in water. Carbon dioxide gas also dissolves in water and helps in photosynthesis in underwater plants. Some gases like nitrogen and hydrogen are not soluble in water. Water is an important part of our body, it helps in dissolving a large number of materials. The substance in which a material is dissolved is called a solvent and water is known as the universal solvent. The only drawback with water is that it cannot dissolve all the materials.
Mass
Mass is a property that measures how heavier or lighter an object is. It is the amount Of substance that makes up an object. Sometimes, the word weight is used instead of the mass of an object. Weighing balance is used to measure the weight of objects. The units to measure mass are kilogram (kg) and gram (g).
When we weigh objects, we observe that some objects are heavier while some are lighter. So, the heavier object is said to have more mass, and the object Weighing a lighter paper cup is said to have less mass.
Space and Volume
Space is the amount of area an object occupies, which can vary depending on its shape and size. The amount of space occupied by a liquid is called its volume. The volume can be measured by using two units litre (L) and millilitre (mL). Water bottles in the market are of different sizes and quantities, with labels like 1L, 500 mL, 250 mL, etc. This label indicates the volume of water, a water bottle can hold.
The SI unit (International System of Units) of mass is the kilogram, it is abbreviated as kg.
The SI unit of volume is the cubic meter, abbreviated as, m3.
It is important to remember that 1 m3 = 1000 L.
Matter
Mass and volume are the two properties that are possessed by all the materials. Anything that occupies space and has a mass is called matter. Mass measures the quantity of matter present in an object and Volume measures the space occupied by matter present in an object. Thus, by measuring the mass and volume of an object, we can tell that an object contains matter, and mass and volume are the two contributing factors for understanding matter. Objects are made up of materials, which are also types of matter. All the materials around us are examples of matter, like, water, bricks, glass, air, etc.
→ Object: A thing that can be seen and touched.
→ Material: Any substance which is used to create an object.
→ Hard Materials: Materials that are difficult to compress or scratch.
→ Soft Materials: Materials that can be compressed or scratched easily.
→ Transparency: The property of a material that allows the light to pass through it.
→ Transparent Materials: Materials through which an object can be seen clearly.
→ Translucent Materials: Materials through which we can see the object but not clearly.
→ Opaque Materials: Materials through which we cannot see at all.
→ Soluble Materials: Materials that disappear when mixed in water, i.e. they dissolve in water.
→ Insoluble Materials: Materials that do not disappear when mixed with water, even if we stir them for a long time.
→ Mass: It is the property that measures how heavier or lighter an object is.
→ Space: The amount of area an object occupies, which can vary depending on its shape and size.
→ Volume: The amount of space occupied by a liquid.
→ Matter: Anything that occupies space and has a mass.