CBSE Class 9 Science note ch 1 Matter in Our Surr..

CBSE Class 9 Science note ch 1 Matter in Our Surroundings

CBSE Class 9 Science |notes|My Academic Era

CBSE Class 9 Science note ch 1 Matter in Our Surroundings


Anything that takes up space is called matter.                                    Example:  air, water, plants, sun, and cloud etc.

# Modern scientists are classified on the basis of physical property and chemical nature. 

Physical Nature Of Matter

1). Matter is made up of particles.                                                         2). How small are these particle of matter?                                          •  the particle of matter are very small there is small beyond our imagination. 

Characteristics Of Particle Of Matter

1). Particle of matter have space between them.                                 2). Particle of matter are continuously moving.                                  3). Particle of matter attract each other. 

States of matter


  • Solid have definite shape.
  • They have distinct boundary and fixed volumes.
  • Solid have negligible compressibility
  • When subjected to external force, the solid has a tendency to retain its shape
  • Solids can break under force, but their shape is difficult to change, so they are rigid.


  • Liquid have no fixed shape.
  • Liquid have fixed volume.
  • Liquids flow and change shape, so is not rigid, but can be called a fluid.
  • Liquid have Negligible  Compressibilty.


  • Gases are highly/much compressible than solid and liquid.
  • Particles spin randomly at high speeds.  Particles hit the wall of container and each other.
  • They expand to fill their containers.
  • They occupy far more space than the liquids or solids from which they form.

IMPORTANT POINT :-  The attraction force between particles is maximum/ High in solids, intermediate/ Medium in liquids and minimum/Low in gases .

Can Matter Change Its State? 

• The states of matter are interlinked. The state of a substance can be changed by changing the temperature or pressure.



Yes, When heated or cooled, the substance can change from one state to another.

The kinetic energy of the particle increases by increasing the temperature of the solid. Vibration starts with greater speed due to increase in kinetic energy of particle. The energy supplied by heat dissipates the force of attraction between the particles. The particles leave their field positions and begin to move more freely. When the solid melts, this state is liberated and is converted to a liquid temperature, at which a solid melts to become a liquid at atmospheric pressure called its melting point.


By implementing pressure, we can bring close and close to the particles of substance. So the pressure can be converted into liquids by applying concrete and can be converted into more pressure fluid gases to move forward.

Apply pressure and reduce temperature can be gas liquid.


Evaporation is a type of Vapourition which is on the surface of the liquid because it turns into gas phase. It is surface phenomena.

1)Factor Affecting Evaporation

  • An increase of surface area :                                                                        evaporation is a surface phenomena if the surface area is increased the rate of evaporation increases.
  • An increase of temperature:                                                                              With the increase in temperature, more number of particles get kinetic energy to go into vapor state.
  • A decrease in humidity:                                                                                      Humidity is the amount of water vapor present in the air. The air around us cannot hold more than a certain amount of water vapor at a certain temperature. If the amount of water in the air is already there then the rate of evaporation decreases.
  • An increase in wind speed:                                                                                It is common observation that the cloth dries rapidly on a winding day. With the increase in air. The water vapor particle moves away with the air, decreasing the amount of surrounding vapor.

2) HOW DOES Evaporation CAUSE  COOLING? 

During the evaporation process, fluid particles obtain energy from their surroundings to overcome the force of attraction between them. This causes loss of heat energy to the surroundings which is why evaporation causes cooling.

3) why should we wear cotton clothes in summer? 

We wear cotton clothes during summer because cotton absorbs sweat from the body, exposing the atmosphere for easy evaporation. As we sweat more during summer and cotton clothes absorb sweat and help cool the body. Cotton allows better air circulation which helps absorb and remove body moisture due to perspiration through evaporation.

3) Why do we see water droplets on the outer surface of a glass containing Ice cold water? 

Water vapor in the air, when exposed to a cold glass of water, loses energy and converts into a liquid state, which we see as water droplets.                                                                      IMPORTANT POINT:- This is called condensation.


CBSE Class 9 Science note ch 1 Matter in Our Surr..

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