Activity Based Science Learning >Dancing Bottle

Introduction  - You might have heard about a sprinkler and also seen water being sprinkled with its help in all directions in the gardens. Usually, a sprinkler is used for irrigation purposes in agriculture or in gardens. Using it a large area of the land can be irrigated at a time. Depending on the requirement different kinds of sprinkler   are available in the market. Here, we will make a sprinkler using a plastic bottle and discuss its science. While sprinkling water the bottle also dances which adds to the joy of this experiment. 

Required material -   Two plastic bottles of square cross-section, thread.  

Procedure : 

1.         Place a bottle of square cross-section in front of you. It has four large surfaces. Make a hole on the right lower side of any of these surfaces. To make the hole you may use the spoke of a bicycle, heat it on a candle flame and then insert it into the plastic. The job of making the hole should preferably be done in the presence of some elder persons. Make similar holes in this manner on the right lower sides of all the four surfaces.

2.         Unscrew the cap of the bottle and tie a thread near its mouth in say a manner that on hanging the bottle by holding the thread it hangs vertically.

3.         With the help of the thread hold the bottle at a height of about 1metre above a plastic tub.

4.         Ask your friend to fill water in the bottle using a mug.

5.         Water starts flowing out of the bottle and the bottle also starts rotating. 

Discussion : Water  streaming our of the holes is understandable but why was the bottle start dancing, after all? Actually, the water while flowing out of the bottle exerts a pressure on it in the backward direction. This is in accordance with Newton’s third law. Water contained in the bottle pushes the water out near the hole which makes water come out of the hole. As reaction of this, the outflowing water pushes the water in the bottle backward. As the hole has been male at the corner, the force being exerted on this part of the bottle will try to rotate it. The forces acting on the four faces will rotate the bottle in the same direction and so the bottle starts dancing. The water flowing out of the dancing bottle spreads in all the directions and presents the scene of a sprinkler. 

Do and think A little more – What will happen if  on a bottle of square cross-section, holes one made on the right lower sides of two of its surfaces while holes are made on the left lower side of its remaining two surfaces? Will the bottle rotate? If not why? Think, Try the same experiment with a bottle of hexagonal cross-section having six faces. Is the speed of rotation of the bottle affected? Take another bottle of square cross-section and make holes on left lower sides of its surfaces. Hang this bottle by tying thread on it and fill in with water. What is the difference between dancing of this and the first bottle?




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