Notes For All Chapters – General Science Class 8
1. Introduction
- Man-made materials are materials that do not exist naturally and are created by humans using natural substances.
- These materials have special properties like durability, flexibility, and resistance to water and heat.
- Examples: Plastic, Glass, Thermocol, and Synthetic Fibers.
2. Types of Materials
(A) Natural Materials
- These are materials found in nature.
- Examples: Wood, Cotton, Silk, Jute, Rubber, and Metals.
(B) Man-Made Materials
- These are created by humans using natural substances.
- Examples: Plastic, Glass, Thermocol, Synthetic Fibers, and Teflon.
3. Plastic
(A) What is Plastic?
- Plastic is a synthetic material made from petroleum and natural gas.
- It is made using a process called polymerization, where small molecules (monomers) join to form long chains (polymers).
(B) Types of Plastics
| Type | Description | Examples |
|---|---|---|
| Thermoplastics | Can be melted and reshaped multiple times. | PVC, Polythene, Nylon |
| Thermosetting Plastics | Once molded, they cannot be reshaped. | Bakelite, Melamine, Teflon |
(C) Uses of Plastic
- PVC: Used in pipes, electric wires, raincoats, and toys.
- Polythene: Used for plastic bags, bottles, and packaging.
- Bakelite: Used in electric switches, handles of cooking utensils.
- Teflon: Used for non-stick cookware and waterproof clothing.
(D) Harmful Effects of Plastic
- Plastic is non-biodegradable, meaning it does not decompose easily.
- It pollutes soil, rivers, and oceans, harming animals and the environment.
- Burning plastic releases toxic gases, causing air pollution.
(E) How to Reduce Plastic Pollution?
- Use cloth or jute bags instead of plastic bags.
- Recycle and reuse plastic items.
- Avoid single-use plastics like plastic straws, cups, and plates.
4. Glass
(A) What is Glass?
- Glass is a transparent, hard material made by heating sand (silica), soda, and lime at high temperatures.
- It does not react with most chemicals and is waterproof.
(B) Types of Glass and Their Uses
| Type of Glass | Uses |
|---|---|
| Lead Glass | Used in electric bulbs and radiation shielding. |
| Optic Glass | Used in lenses, microscopes, and cameras. |
| Tempered Glass | Used in car windows and mobile screens. |
| Borosilicate Glass | Used in laboratory glassware and kitchen utensils. |
(C) Uses of Glass
- Windows and mirrors.
- Bottles and containers.
- Lenses for spectacles, cameras, and microscopes.
- Laboratory equipment like test tubes and beakers.
5. Thermocol (Polystyrene Foam)
(A) What is Thermocol?
- Thermocol is a lightweight plastic material made from polystyrene.
- It is used for packaging, insulation, and decoration.
(B) Disadvantages of Thermocol
- Non-biodegradable and harmful to the environment.
- Releases toxic gases when burned.
- Should be replaced with biodegradable packaging materials.
6. Synthetic Fibers
(A) What are Synthetic Fibers?
- Man-made fibers produced using chemicals and petroleum products.
- Examples: Nylon, Polyester, Acrylic, and Rayon.
(B) Types and Uses of Synthetic Fibers
| Synthetic Fiber | Uses |
|---|---|
| Nylon | Used in ropes, seat belts, parachutes, and stockings. |
| Polyester | Used in clothes, curtains, and bottles. |
| Acrylic | Used in woolen clothes and blankets. |
| Rayon | Used in sarees, bed sheets, and furniture covers. |
7. Environmental Impact of Man-Made Materials
| Material | Effect on Environment | Solutions |
|---|---|---|
| Plastic | Pollutes land and water. Harmful to animals. | Use cloth bags, recycle plastic. |
| Glass | Takes a long time to decompose. | Recycle glass bottles and items. |
| Thermocol | Non-biodegradable, produces toxic gases. | Avoid its use in packaging. |
| Synthetic Fibers | Do not decompose, pollute water. | Use natural fibers like cotton. |
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