General Science Notes Chapter 3 Class 7 Maharashtra Board

Notes For All Chapters – General Science Class 7

1. Introduction

• Air, water, and soil are important natural resources necessary for life on Earth.
• Air is a mixture of gases that supports life.
• Water is essential for drinking, farming, and industries.
• Soil provides nutrients for plant growth.

2. Composition of Air

Air is a mixture of gases like:

• Nitrogen (78%) – Helps in plant growth.
• Oxygen (21%) – Needed for breathing.
• Carbon dioxide (0.03%) – Used by plants for photosynthesis.
• Other gases (1%) – Includes argon, helium, and water vapor.

Properties of Air

• Air has weight – A blown-up balloon is heavier than an empty one.
• Air occupies space – An empty bottle still has air inside it.
• Air exerts pressure – Used in syringes, straws, and tire filling.
• Air can expand and contract – Hot air expands, and cold air contracts.

3. Importance of Air

• Supports Life – Oxygen is essential for humans and animals, while plants need carbon dioxide.
• Helps in Sound Transmission – Sound travels through air in the form of vibrations.
• Controls Weather – Air movements cause wind, rain, and storms.

4. Air Pressure

Definition: The force exerted by air on everything around us.

Measured by: A barometer.

Uses of Air Pressure:

• Drinking with a straw.
• Using a syringe.
• Flying airplanes.

5. Water – The Universal Solvent

Water is called the universal solvent because it dissolves many substances.

Properties of Water:

• Has no shape – Takes the shape of the container.
• Can change state – Solid (ice), Liquid (water), and Gas (steam).
• Expands when frozen – Ice is lighter than water and floats.

Uses of Water

• Drinking and cooking.
• Agriculture (irrigation).
• Industries and electricity production.

6. Density of Water

• Seawater is denser than rainwater due to dissolved salts.
• Objects float better in seawater than in freshwater.

7. Soil – Formation and Importance

How is Soil Formed?

• Soil is formed by the breakdown of rocks due to wind, rain, and temperature changes over thousands of years.

Types of Soil

1. Sandy Soil – Large particles, holds less water.
2. Clayey Soil – Small particles, holds more water.
3. Loamy Soil – A mix of sand and clay, best for farming.

Importance of Soil

• Provides nutrients to plants.
• Helps in water absorption.
• Used in building houses and making pottery.

8. Soil Testing

• Farmers test soil to check the nutrient levels before farming.
• Helps in choosing the right fertilizers for better crops.