CBSE Class 9 Science Notes: Matter in Our Surroundings

Matter and Its Existence

Let’s dive into the fascinating world of matter! Everything around us, from the air we breathe to the chair we sit on, is made of matter. Matter is defined as anything that has mass and occupies space.

Definitions:

• Mass: A measure of the amount of ‘stuff’ an object contains.
• Volume: The amount of space an object occupies.

Examples from Daily Life:

• Air: Fills balloons, tires, and is essential for breathing.
• Water: Found in rivers, oceans, and is vital for life.
• Books: Possess mass and volume.
• Your body: Composed of various types of matter.

Particles of Matter: The Building Blocks

Matter isn’t continuous; it’s made up of tiny particles! These particles can be atoms or molecules.

Core Principles:

• Particles of matter are very small.
• Particles of matter have space between them.
• Particles of matter are constantly moving.
• Particles of matter attract each other.

Characteristics of Particles:

• Movement: Particles are in constant motion (kinetic energy). Higher the temperature, higher the motion.
• Space: There is space (interparticle space) between the particles.
• Attraction: Particles attract each other (force of attraction, which varies in solids, liquids, and gases).

States of Matter: Solid, Liquid, and Gas

Matter exists in three main states: solid, liquid, and gas. These states differ in the arrangement and behavior of their particles.

Definitions:

• Solid: Definite shape and volume.
• Liquid: Definite volume but no definite shape (takes the shape of the container).
• Gas: Neither definite shape nor volume (fills the entire container).

Properties of Different States of Matter

Each state of matter exhibits unique properties based on the arrangement and behavior of its particles.

Comparison Table:

Changes of State: Transforming Matter

Matter can change its state by changing temperature or pressure.

Definitions:

• Melting: Solid changing to liquid (e.g., ice to water).
• Freezing: Liquid changing to solid (e.g., water to ice).
• Condensation: Gas changing to liquid (e.g., steam to water).
• Sublimation: Solid changing directly to gas (e.g., dry ice to carbon dioxide gas).

Key Concepts:

• Melting Point: The temperature at which a solid melts at atmospheric pressure.
• Boiling Point: The temperature at which a liquid boils at atmospheric pressure.

Evaporation and Factors Affecting It

Evaporation is the process where a liquid changes into a gas below its boiling point.

Factors Affecting Evaporation:

• Surface Area: Larger surface area increases evaporation (e.g., spreading clothes to dry faster).
• Temperature: Higher temperature increases evaporation (e.g., drying clothes on a sunny day).
• Humidity: Lower humidity increases evaporation (e.g., drying clothes on a dry day).
• Wind Speed: Higher wind speed increases evaporation (e.g., drying clothes in the wind).

Cooling Caused by Evaporation

Evaporation causes cooling.

Core Principle: When a liquid evaporates, the particles with higher kinetic energy escape, leaving behind the lower energy particles, thus decreasing the average kinetic energy which reduces the temperature (cooling effect).

Examples:

• Sweat: Evaporation of sweat cools our body.
• Putting acetone on the skin: Gives a cooling sensation.