Activity Based Science Learning >The obedient bottle


Introduction:

Present around us is the pressure due to the atmosphere. We have read this in books and also heard about it. Here, we will perform a single experience to experience it. 

Procedure:

1.         Take a medium sized plastic bottle.

2.         Make a large number of small holes at the bottom of the bottle.

3.         You may make these holes with the help of a needle or safety pin.

4.         Make a small hole also at the upper part of the bottle below its mouth i.e. on its neck.

5.         Keep a tub on the ground.

6.         Keep the bottle above the tub at a height of about half a metre.

7.         Fill the bottle with water and close its lid. The level of water in the bottle must remain below the hole made on its neck. 

What will happen?

Certainly, the water will start flowing out through the holes made at the bottom of the bottle. If you so desire, you may even stop the water flowing out from the bottom. Think how this can be done? 

Just put your finger on the hole which you made on the neck of the bottle, and the water will shop flowing out Therefore, when you want the water to flow out just remove your finger from the hole and when you want to stop the water flow, simply block the hole with your finger. In this way, making use of only a plastic bottle we are able to make an obedient device using which we can understand the effect of air pressure. 

Discussion:

Let us try to understand how this happens. When the holes made at the bottom of the bottle as well as the hole on its neck are open, in that case due to the weight of the water column the total pressure on the bottom of the bottle is more that the pressure of the air outside the bottle. As a result, the water flows out from the holes at the bottom of the bottle. The air outside the bottle exert its influence so that  water does not flow out while the pressure of water inside the bottle tries to force the water out of the bottle. The hole near the neck. of the bottle being open, the pressure of the air near the neck of the bottle is equal to the atmospheric pressure. This adding to the pressure of water makes the total pressure inside the bottle greater than the atmospheric pressure. As a result, the water flows out of the holes. Now, if you block the hole on the neck of the bottle with your finger, you will see that the water stops flowing out. Does the water stop flowing as soon as you put your finger on the hole? If you carefully observe you will find that the water stops flowing out within just a few moments and not immediately. It happened so because when you close the hole on the bottle’s neck, the space above the water column get cut off from the atmospheric air. Consequently, as little water flows out from the holes, the volume of the air locked inside the bottle above the water column increases and due to this increased volumes the pressure of the locked air decreases. Now, the combined pressure of the locked air above the water column and the water column are not able to exceed the atmospheric pressure being executed on the holes. And therefore, the water stops flowing out. 

Do and think A little more: Make two instead of one hole on the neck of the bottle. What happens? Repeat the experiment by keeping the lid of the bottle open. It is necessary to make a large number of holes at the bottom? Will only a single hole not do?

 

 

 





 


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