4. Sorting Materials into Groups
Introduction: Look around you! You will see chairs, tables, books, clothes, and toys. All these objects are made of different materials. Some are made of wood, some of plastic, and some of metal. We group objects to study their properties conveniently.
Properties of Materials
Why is a tumbler not made with a piece of cloth? Because it needs to hold water! We choose a material to make an object based on its properties and the purpose of the object.
1. Appearance: Materials look different from each other.
- Lustre: Some materials shine (Gold, Silver, Freshly cut iron). These are usually metals.
- Dull: Materials that do not shine (Wood, Cardboard).
ACTIVITY 3: Lustre
Observation: Cut pieces of materials like copper wire, aluminum sheet. You will see they shine at the freshly cut surface. This shine is called Lustre.
2. Hardness:
- Soft: Materials that can be compressed or scratched easily (Cotton, Sponge).
- Hard: Materials that are difficult to compress (Iron, Wood).
Soluble or Insoluble?
Activity 4: Keep some solid substances like salt, sugar, sand, chalk powder, and sawdust. Add them to water and stir.
- Soluble: Substances that completely disappear or dissolve in water. (Salt, Sugar).
- Insoluble: Substances that do not mix with water and settle down. (Sand, Chalk powder, Sawdust).
Note: Water plays an important role in the functioning of our body because it can dissolve a large number of substances.
SOLVED IN-TEXT QUESTION: Boojho
Q: Boojho suggests that we also check if the liquids that we used in Activity 5 mix well with some liquid other than water.
Ans: Yes, some liquids like vinegar and lemon juice mix well with water (Miscible), while oil does not mix and forms a separate layer (Immiscible).
Float or Sink?
Some materials are lighter than water and float on it (Dried leaves, Plastic ball, Wood). Others are heavier and sink to the bottom (Iron key, Stone, Coin).
Transparency
- Transparent: Materials through which things can be seen clearly. Examples: Glass, Water, Air.
- Opaque: Materials through which you cannot see. Examples: Wood, Metal, Cardboard.
- Translucent: Materials through which objects can be seen, but not clearly. Examples: Oiled paper, Frosted glass.
ACTIVITY 6: Translucent
Recall: Remember the oily patch on paper in Chapter 2? That was translucent too! Shine a torch through your palm; your palm allows some light to pass, so it is also translucent.
Chapter Summary
- Objects around us are made up of a large variety of materials.
- A given material could be used to make a large number of objects. It is also possible that an object could be made of a single material or of many different types of materials.
- Different types of materials have different properties.
- Some materials are shiny in appearance while others are not. Some are rough, some smooth. Some hard, some soft.
- Some materials are soluble in water whereas some others are insoluble.
- Some materials such as glass, are transparent and some others such as wood and metals are opaque. Some materials are translucent.
- Materials are grouped together on the basis of similarities and differences in their properties.
- Things are grouped together for convenience and to study their properties.
Exercise Q1
Q: Name five objects which can be made from wood.
Exercise Q2
Q: Select those objects from the following which shine: Glass bowl, plastic toy, steel spoon, cotton shirt.
Exercise Q3: Match the objects
- Book -> Paper
- Tumbler -> Glass/Plastic
- Chair -> Wood
- Toy -> Plastic
- Shoes -> Leather
Exercise Q4: True or False
- Stone is transparent, while glass is opaque. (False)
- A notebook has lustre while eraser does not. (False)
- Chalk dissolves in water. (False)
- A piece of wood floats on water. (True)
- Sugar does not dissolve in water. (False)
- Oil mixes with water. (False)
- Sand settles down in water. (True)
- Vinegar dissolves in water. (True)
Exercise Q5: Find the odd one out
- Chair, Bed, Table, Baby, Cupboard -> Baby (Living thing)
- Rose, Jasmine, Boat, Marigold, Lotus -> Boat (Not a flower)
- Aluminum, Iron, Copper, Silver, Sand -> Sand (Not a metal)
- Sugar, Salt, Sand, Copper sulphate -> Sand (Insoluble)
Key Facts and Definitions
Lustre: The shine or brightness of a material (usually metals like Gold, Silver, Iron, Copper).
Some metals lose their shine and appear dull because of the action of air and moisture on them.
- Soluble Substances: Dissolve completely in water (Sugar, Salt).
- Insoluble Substances: Do not dissolve in water (Sand, Oil).
- Miscible Liquids: Liquids that mix well with water (Vinegar, Lemon juice).
- Immiscible Liquids: Liquids that do not mix with water and form a separate layer (Oil, Kerosene).
| Type | Description | Examples |
|---|---|---|
| Transparent | Can see clearly | Glass, Water |
| Translucent | Can see partially | Oiled paper |
| Opaque | Cannot see at all | Wood, Metal |
- Hard Material: Cannot be compressed easily (Iron, Stone).
- Soft Material: Can be compressed or scratched easily (Cotton, Sponge).
- Rough Texture: Uneven surface (Bark of a tree, Sandpaper).
- Smooth Texture: Even surface (Glass sheet, Flower petal).