CBSE – 9th Standard Science

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Chapter 1 – Matter in our surroundings

Physical Nature of Matter

  • Everything in this universe is made up of material which scientists have named “matter”.
  • The air we breathe, the food we eat, stones, clouds, plants and animals, even a small drop of water or a particle of sand everything is matter.
  • Matters have both mass and volume.
  • Early Indian philosophers classified matter in the form of five basic elements – the

“Panch Tatva”, air, earth, fire, sky and water. According to them everything, living or nonliving, was made up of these five basic elements.

  • Matter around us exists in three different states Solid, Liquid and Gas.

Characteristics of Particles of Matter:

PARTICLES OF MATTER HAVE SPACE BETWEEN THEM

PARTICLES OF MATTER ARE CONTINUOUSLY MOVING

Particles of matter are continuously moving, that is, they possess what we call the kinetic energy. As the temperature rises, particles move faster. So, with increase in temperature the kinetic energy of the particles also increases.

PARTICLES OF MATTER ATTRACT EACH OTHER

Particles of matter have force acting between them. This force keeps the particles together. The strength of this force of attraction varies from one kind of matter to another.

States of Matter

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  • These states of matter arise due to the variation in the characteristics of the particles of matter.
  • On increasing the temperature of solids, the kinetic energy of the particles increases.
  • The temperature at which a solid melts to become a liquid at the atmospheric pressure is called its melting point.
  • The melting point of a solid is an indication of the strength of the force of attraction between its particles.
  • The process of melting, that is, change of solid state into liquid state is also known as fusion.
  • A change of state directly from solid to gas without changing into liquid state (or vice versa) is called

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  • Applying pressure and reducing temperature can liquefy gases.
  • Pressure and temperature determine the state of a substance, whether it will be solid, liquid or gas.

Evaporation

  • Boiling is a bulk phenomenon. Particles from the bulk (whole) of the liquid change into vapour state.
  • Phenomenon of change of a liquid into vapours at any temperature below its boiling point is called evaporation.
  • Evaporation is a surface phenomenon If the surface area is increased, the rate of evaporation increases.
  • With the increase of temperature, more number of particles get enough kinetic energy to go into the vapour state.
  • Humidity is the amount of water vapour present in air.
  • If the amount of water in air is already high, the rate of evaporation decreases.

Now scientists are talking of five states of matter: Solid, Liquid, Gas, Plasma and Bose-Einstein Condensate.

Plasma: The state consists of super energetic and super excited particles. These particles are in the form of ionised gases

Bose-Einstein Condensate:  The BEC is formed by cooling a gas of

extremely low density, about one-hundred-thousandth the density of normal air, to super low temperatures.