Materials Around Us — NCERT Solutions, AI Tutor & Practice

Understand: Everything around us that we can see and touch is an object.

Analyze:

• An object is a thing that has a shape and can be used for a purpose, e.g. a chair, a spoon, a book.
• A material is the substance from which an object is made, e.g. wood, steel, plastic.

Example: A chair is an object, and it may be made of the material wood. The same material (wood) can make different objects like a table, a door, or a pencil.

Conclude: Objects are the things we use; materials are what those things are made of.

Understand: Some objects are made using several different materials together.

Analyze — Example of a pencil:

• The outer body is made of wood.
• The writing part (lead) is made of graphite.
• The eraser at the top is made of rubber.
• The metal ring holding the eraser is made of metal.

Conclude: Yes, a single object can be made from many materials, because different parts of the object need different properties.

Understand: To study materials easily, we group them based on their properties.

Analyze — Properties used for grouping:

1. Appearance — shiny (lustrous) or dull.
2. Hardness — hard or soft.
3. Solubility — soluble or insoluble in water.
4. Transparency — transparent, translucent, or opaque.
5. Ability to float or sink in water.

Conclude: Any two properties can be used, for example hardness and appearance, to sort materials into groups.

Understand: Lustre is the shine on the surface of a material.

Analyze:

• Materials with shine are called lustrous.
• Materials without shine are called non-lustrous (dull).

Lustrous materials: gold, silver, copper, iron (freshly cut).

Non-lustrous materials: wood, chalk, cloth, paper.

Conclude: Most metals are lustrous, which is why they are used to make jewellery and decorative items.

Understand the terms:

• Transparent — we can see clearly through it.
• Translucent — we can see partly (blurred) through it.
• Opaque — we cannot see through it at all.

Analyze and classify:

| Category | Materials | |----------|-----------| | Transparent | glass, plain water | | Translucent | butter paper, oiled paper | | Opaque | wooden door, cardboard |

Conclude: The amount of light passing through a material decides whether it is transparent, translucent, or opaque.

Understand:

• A material that mixes fully and disappears in water is soluble.
• A material that does not mix and stays separate is insoluble.

Analyze — Example:

• Soluble: sugar dissolves completely in water and cannot be seen.
• Insoluble: sand settles down at the bottom and does not dissolve.

Conclude: Solubility is the property of a material to dissolve in water. Salt and sugar are soluble; sand and chalk powder are insoluble.

Understand: Not all liquids dissolve in water — some mix and some do not.

Analyze:

• Vinegar mixes completely with water and forms a single uniform liquid. So vinegar is soluble (miscible) in water.
• Coconut oil does not mix with water; it floats and forms a separate layer on top. So coconut oil is insoluble (immiscible) in water.

Conclude: Some liquids are soluble in water while others are not, just like solids.

Understand: Whether a material floats or sinks depends on its material and how heavy it is for its size.

Analyze:

• Materials that stay on the surface of water float.
• Materials that go down to the bottom sink.

Float on water: a dry piece of wood, a plastic ball, a thermocol piece.

Sink in water: an iron nail, a coin, a stone.

Conclude: Floating and sinking is a property used to group materials. The same material (like a flat piece of metal shaped as a boat) can sometimes float, but generally metals sink and light materials float.

Understand: Every object needs a material that suits its use.

Analyze:

• A water bottle must be made from a material that does not let water pass and does not dissolve — so plastic or glass is used, not paper.
• A window pane must let light in, so transparent glass is used.
• A cooking pan must not melt, so metal is used.

Conclude: Knowing properties like transparency, solubility, hardness, and whether a material lets water through helps us choose the right material so the object works well and lasts long.

Understand:

• Hard materials cannot be easily compressed or scratched.
• Soft materials can be easily pressed or squeezed.

Analyze and classify:

| Hard materials | Soft materials | |----------------|----------------| | iron, stone | cotton, sponge, rubber band |

Note: Chalk is fairly soft — it can be scratched and broken easily, so it is placed among the softer materials.

Conclude: Hardness is a useful property for grouping. Hard materials are used where strength is needed (tools, buildings), while soft materials are used for comfort (clothes, cushions).

Understand: We can separate a mixture using the different properties of its materials.

Analyze:

• Sawdust is light and floats on water.
• Iron nails are heavy and sink to the bottom; they are also magnetic.

Steps to separate:

1. Add the mixture to water — the sawdust floats on top and can be skimmed off.
2. The iron nails sink to the bottom.
3. Alternatively, a magnet can be used to pull out the iron nails, since iron is attracted to a magnet.

Conclude: By using the properties floating/sinking and magnetic attraction, the two materials can be easily separated.

Analyze each statement:

(a) False. Most metals are lustrous (shiny), not non-lustrous.

(b) False. Chalk is insoluble in water — it does not dissolve and settles down.

(c) True. Objects are indeed made from one or more materials.

(d) True. Air is transparent because we can see clearly through it.

Conclude: Testing statements against the definitions of properties helps us decide what is correct.