Take water in pot and heat till it boils. Pour this boiled water into a plastic bottle. After sometime,drain water from the plastic bottle and tightly cap the bottle. Now,the cold water pours on bottle. What do you see? Why does the bottle collapse ?After draining the hot water from bottle,water vapours are trapped inside the bottle. When cold water is poured on the bottle then water vapours cool into liquid so the amount of water vapour inside the bottle reduces,thus the resultant pressure also reduces and bottle collapses due to external air-pressure. Thus we can say that air has pressure.Pressure exerted on us surrounding atmosphere is called atmospheric pressure. At sea level, the average value of atmospheric pressure is 101325 pascal.Air flows from high pressure area to low pressure area. So, we can say that air blows due to the difference in air pressure. When air blows with speed, the air-pressure is reduced on the roof but air-pressure increase inside the rooms.Due to this tin-sheds or khaprels' are blown away from weak homes.1. What do you see?2. Why bottle gets compressed?