Science Class 9 - Chapter 1 | Matter in Our Surroundings

 Class 9 – Science Notes and Question answer - Chapter1

Matter-

Anything which occupies space and has mass is called matter .

e.g  Air , water , sugar , silver etc.

classification of  matter

( a)  On the basis of its physical properties-

matter is classified as solids , liquids and gases .

( b ) On the basis of chemical properties -

Matter is classified as elements , compounds and mixtures .

 

Particle – Smallest part of matter is called particle. Particle is atom or molecule.

Characteristics of Particles of Matter -

( i ) The particles of matter are very , very small

( ii ) The particles of matter have spaces between them

( iii ) The particles of matter are constantly vibrating or moving

( iv ) The particles of matter attract each other

 

Existence of particles and their motion in matter -

Existence of particles in matter and their motion comes from the experiments on diffusion and Brownian motion .

( a) Diffusion -  The existence of diffusion gives us two conclusions about the nature of matter :

( i ) Matter is made up of tiny particles

( ii ) The particles of matter are constantly moving .

Experiment -   

* When the potassium permanganate crystal is put in water , its particles separate from one another . These purple coloured particles of potassium permanganate spread throughout water making the whole water look purple .

* On dissolving , the particles of potassium permanganate get into the spaces  between water molecules.

 

( b ) Brownian motion – The zig - zag movement of the small particles suspended in a liquid ( or gas ) is called Brownian motion .

* Concept of Brownian motion is given by Robert Brown.

* Brownian motion increases on increasing with temperature.

The existence of Brownian motion gives us two conclusions about the nature of matter :

( i ) Matter is made up of tiny particles

( ii ) The particles of matter are constantly moving .

Example -

( a ) Brownian motion in liquid-

* The random motion ( or zig - zag way ) of visible particles ( pollen grains ) caused by the much smaller invisible particles of water is an example of Brownian motion in liquid.

* Water is made up of tiny particles which are moving very fast . The pollen grains move on the surface of water because they are constantly being hit by the fast moving particles of water .

 ( b )  Brownian motion in Gas -

*  When a beam of sunlight enters a room , we can see tiny dust particles suspended in air which move  rapidly in a very haphazard way .

* The tiny dust particles move here and there because they are constantly hit by the fast moving particles of air .