NCERT Class 9 Science Textbook for Blind and Visually Impaired Students made Screen Readable by Professor T K Bansal.

• Matter is made up of small particles.

• The matter around us exists in three states- solid, liquid and gas.

• The forces of attraction between the particles are maximum in solids, intermediate in liquids and minimum in gases.

• The spaces in between the constituent particles and kinetic energy of the particles are minimum in the case of solids, intermediate in liquids and maximum in gases.

• The arrangement of particles is most ordered in the case of solids, in the case of liquids layers of particles can slip and slide over each other while for gases, there is no order, particles just move about randomly.

• The states of matter are inter-convertible. The state of matter can be changed by changing temperature or pressure.

• Sublimation is the change of gaseous state directly to solid state without going through liquid state, and vice versa.

• Boiling is a bulk phenomenon. Particles from the bulk (whole) of the liquid change into vapour state.

• Evaporation is a surface phenomenon. Particles from the surface gain enough energy to overcome the forces of attraction present in the liquid and change into the vapour state.

• The rate of evaporation depends upon the surface area exposed to the atmosphere, the temperature, the humidity and the wind speed.

• Evaporation causes cooling.

• Latent heat of vaporisation is the heat energy required to change 1 kg of a liquid to gas at atmospheric pressure at its boiling point.

• Latent heat of fusion is the amount of heat energy required to change 1 kg of solid into liquid at its melting point.

• Some measurable quantities and their units to remember: