CBSE Class-3 Science Chapter-8 Air And Water

 

                          TOPIC- AIR AND WATER

AIR:

⦿Air is present everywhere and all living things need air to survive.

⦿We cannot see the air, but we can feel it.

⦿Air is needed for breathing , burning, sailing boats, flying 

     kites etc.

⦿The thick layer of air that surrounds the earth is called atmosphere.

⦿Air is made up of many gases like nitrogen ,oxygen , carbon dioxide 

     and water vapour.

WATER:

⦿ Like air ,water is also essential for all living things for survival.

⦿We get water when water falls from the sky as rain and fills up oceans, seas, rivers , ponds. Also we get from deep under the ground.

⦿ Water has no fixed shape,It takes the shape of the vessel in which it  is poured. 

⦿Water exists in three different states i.e solid, liquid and gas.

⦿Solid form of water is called ice, liquid form is called water and gas    form is called water vapour.

⦿On Heating or cooling ,water changes its state.

WATER CYCLE:

⦿The important points in water cycle are  evaporation, condensation and precipitation.

 

⦿The rays of the sun fall on oceans, seas, rivers , ponds and lakes.

⦿ This heats up the water ,which changes into water vapour and it rises up .

⦿ The change of water into water vapour on  heating is called evaporation.

⦿High up the sky ,water vapour come in contact with cool air .

⦿ Then it forms tiny water droplets.

⦿ The change of water vapour into water droplets on cooling is called condensation.

⦿These water droplets combine together to form clouds.

⦿On further cooling ,the tiny water droplets join to form bigger droplets inside the clouds.

⦿ The cloud become very heavy and the water  droplets Fall down as rain.

⦿ This is known as precipitation.    

⦿ In very cold places ,water droplets freeze into ice and come down as snow.   

⦿ The rain again fills the rivers , ponds ,seas , lakes.

⦿ The continuous change of  water from one state to another in nature is called “water cycle”.