Constructing a water dam at home

Constructing a water dam at home
You might know that the dams constructed on the rivers have their lower portion much broader than the upper portion. Can you tell why? Take a cylindrical container made of tin. You can use an empty container of talcum powder for this purpose. Divide the cylinder from top to bottom in four equal parts and make three holes in it with the help of a hammer and a nail.

Now keep the tin, either in a tray or at any such place where there is no danger of anything getting spoiled by the spurt of water from the three holes. Then fill the tin fully with water. What do you see when you fill the tin with water? 

Three jets of water start spurting from the holes, don't they? But you will observe that all the three streams are quite different from each other. The jet of water spurting from the lowest hole falls the farthest from the tin and the one coming out of the top hole falls the nearest to the tin. Let me tell you the reason. Come, let us first consider the top hole.
Only that portion of water will spurt out of this hole which is above the level of this hole. Since the water in the lower portion of the tin has not yet come out of this hole, it won't exert any pressure on the water spurting out of this hole.

In the same way, when you consider the lowest hole you will observe that the entire water which is above the level of this hole exerts pressure on the jet spurting out of this hole. And that will definitely be far more than the pressure exerted on the water spurting from the top hole.

Thus, you have seen that in a vessel full of water, the pressure on the lower part is always more in comparison to the pressure felt on the higher part.It is for this reason that the lower portions of the dams are made broader because the pressure decreases as you go upwards.


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