Properties of Materials - Class 6 Notes & Olympiad Questions

What is Matter or Material?

Matter refers to anything that occupies space and has mass. It can be classified into different types based on its composition, state, and properties.

Properties of Material

1. Appearance

Materials can indeed be differentiated based on their appearance. The property that describes the visual appearance of a material is called lustre.
Luster is a useful property for identifying and distinguishing different types of materials based on their visual characteristics.

Lustrous Materials

a) Lustrous materials are those that have a shiny or reflective appearance.
b) Examples of lustrous materials include diamond, aluminium, and gold. These substances reflect light well and appear bright and shiny.
c) It is important to note that almost all metals are lustrous, with varying degrees of shininess.
d) Some metals, like silver and chrome, have a highly reflective surface and appear very shiny. Others, like iron, may have a less reflective surface but still possess some lustre.

Non-lustrous Materials

a) On the other hand, non-lustrous materials do not have a shiny appearance. They may appear dull or non-reflective.
b) Non-metals, such as graphite and wood, generally do not exhibit lustre and have a non-shiny appearance.
c) These materials do not reflect light well and hence do not appear shiny.

2. Hardness

Hardness is a property of materials that describes their resistance to compression. Based on their hardness, materials can be classified as either soft or hard.

Soft Materials

a) Soft materials are those that can be easily compressed or scratched. They have a low resistance to deformation.
b) Examples of soft materials include cotton and rubber.
c) These materials can be easily squeezed or deformed, and they can be scratched or marked with relatively low force.

Hard Materials

a) On the other hand, hard materials are difficult to compress or scratch. They have a high resistance to deformation.
b) Examples of hard materials include wood, rock, and iron. These materials require a significant amount of force to be compressed or scratched.

3. Behaviour Under Force

It's worth noting that materials can also be further classified based on their behaviour under different types of forces. For example:

Brittle materials: These materials are prone to breaking or fracturing when subjected to stress. They do not exhibit significant plastic deformation. Examples of brittle materials include glass and ceramic.

Ductile materials: These materials can be easily drawn or stretched into thin wires without breaking. They exhibit plastic deformation under stress. Examples of ductile materials include copper and gold.

Malleable materials: These materials can be easily shaped or compressed into thin sheets without breaking. They also exhibit plastic deformation under stress. Examples of malleable materials include aluminium and lead.

4. Visibility

Materials can be classified based on their visibility or ability to transmit light. There are three main categories: transparent, translucent, and opaque.

Transparent

a) Transparent materials allow light to pass through them without significant scattering or absorption.
b) Light can travel through them in a straight path, resulting in clear visibility.
c) Examples of transparent materials include air, clear water, and glass.
d) When you look through these materials, you can see objects clearly on the other side.

Translucent

a) Translucent materials allow some light to pass through them, but they scatter or diffuse the light, resulting in a blurry or diffused appearance.
b) Light passes through these materials, but it is not transmitted in a straight path.
c) Examples of translucent materials include frosted glass and oiled paper.
d) When you try to look through these materials, the objects on the other side appear blurry or obscured.

Opaque

a) Opaque materials do not allow light to pass through them at all.
b) They absorb or reflect light, preventing it from transmitting through the material.
c) Examples of opaque materials include wood, metals, and brick.
d) When you try to look through these materials, you cannot see objects on the other side as the light is blocked completely.

The classification of materials based on visibility is important in various applications, such as designing windows, selecting materials for privacy, or understanding how light interacts with different substances.

5. Solubility

Solubility refers to the ability of a substance to dissolve in a particular solvent, such as water.
Based on solubility, substances can be classified as soluble or insoluble, and liquids can be classified as miscible or immiscible with water.

Soluble Substances

a) These are substances that can dissolve or disappear in water.
b) When a soluble substance is added to water and stirred, it forms a homogeneous mixture.
c) Examples of soluble substances include sugar and salt. When you add sugar or salt to the water and stir, they dissolve and become completely mixed with the water, resulting in a clear solution.

Insoluble Substances

a) These are substances that do not mix with water and do not disappear even after stirring for a long time.
b) When an insoluble substance is added to water and stirred, the particles do not break down or disperse in water.
c) Instead, they remain separate and can be seen as suspended particles or settle at the bottom.
d) Examples of insoluble substances include chalk powder and sand. If you add chalk powder or sand to water and stir, they will not dissolve and will remain visibly separate from the water.

Miscible Liquids

a) These are liquids that mix well with water, forming a homogeneous mixture.
b) When miscible liquids are combined with water, they mix completely, forming a single phase.
c) An example of a miscible liquid with water is ethanol (alcohol). If you add ethanol to water, they mix thoroughly, resulting in a homogeneous solution.

Immiscible Liquids

a) These are liquids that do not mix well with water, forming separate layers. When immiscible liquids are combined with water, they do not mix and separate into distinct layers.
b) An example of an immiscible liquid with water is oil. If you add oil to water and stir, they will not mix, and the oil will form a separate layer on top of the water.

6. Density

a) Density is a property of a substance that relates its mass to its volume. It is defined as the mass per unit volume of a material.
b) The density of a substance determines whether it will float or sink in a liquid, such as water.
c) When an object is placed in a liquid, such as water, the buoyant force exerted by the liquid counteracts the force of gravity on the object.
d) Whether the object floats or sinks depends on the relationship between its density and the density of the liquid.

Objects that Float

a) If the density of the object is lower than the density of the liquid (in this case, water), the object will float.
b) The buoyant force acting upward is greater than the gravitational force pulling the object downward.
c) Examples of objects that float in water include a leaf and cork.

Objects that Sink

a) If the density of the object is greater than the density of the liquid, the object will sink.
b) The gravitational force pulling the object downward is greater than the buoyant force acting upward.
c) Examples of objects that sink in water include a metal spoon and a coin.

7. Conductivity

Conductivity refers to the ability of a material to conduct or transmit heat or electricity. Materials can be classified as conductors or insulators based on their conductivity properties.

Conductors

a) Conductors are materials that allow the flow of electric current or the transfer of heat through them easily.
b) These materials have a high conductivity.
c) Copper and silver are examples of good conductors of both heat and electricity.
d) They have free electrons that are capable of moving and carrying the electric charge or heat energy efficiently.

Insulators

a) Insulators, also known as non-conductors, are materials that do not allow the flow of electric current or the transfer of heat through them easily.
b) These materials have a low conductivity.
c) Examples of insulators include wood, plastic, rubber, and cork.
d) They have tightly bound electrons that do not move easily, restricting the flow of electric charge or heat energy.