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www.GOALias.blogspot.comFig. 8.2 Can with hot water being cooledCan you guess why the shape of thecan gets distorted?If you cannot get a tin can, take asoft plastic bottle. Fill it with hot water.Empty the bottle and immediately capit tightly. Place the bottle under runningwater.Recall now some of your experiences.When you fly a kite, does the windcoming from your back help?If you are in a boat, is it easier torow it if there is wind coming frombehind you?Do you find it difficult to ride a bicycleagainst the direction of the wind.You know that we have to fill air intothe bicycle tube to keep it tight. Also,you know that a bicycle tube overfilledwith air may burst. What is the air doinginside the tube?Discuss with your friends how theair in the bicycle tube keeps it in shape.All these experiences show that theair exerts pressure. It is due to thispressure that the leaves of trees,banners, or flags flutter when the windis blowing. You can list some moreexperiences which show that the air haspressure.Let us now try to explain why thecan (or the bottle) gets distorted. Aswater is poured over the can, somesteam in the can condenses into water,reducing the amount of air inside. Thepressure of air inside the can decreasesthan the pressure exerted by the airfrom outside the can. As a result thecan gets compressed.This activity again confirms that airexerts pressure.8.2 HIGHSPEEDWINDSAREACCOMPANIEDBY REDUCEDAIRPRESSUREActivity 8.2Fig. 8.3 Blowing into the bottleCrumple a small piece of paper intoa ball of size smaller than the mouth ofan empty bottle. Hold the empty bottleon its side and place the paper ball justinside its mouth. Now try to blow onthe ball to force it into the bottle. Trythe activity with bottles of different sizes.Challenge your friends if they can force, SWINDSINDS, , STORMSAND CYCLONES8181