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A man is sitting on a boat which is floating in a pond. If the man drinks some water from the pond, What happens to the level of water?

According to me, the level of the water in the pond should decrease. However, when I tried to perform it on a mini scale (I really did not have any means to get the correct answer) by putting a spoonful of water in the toy boat instead of a man drinking water (well, I hope both the actions are equivalent), I found that the level of water remains same. How?

Related: but doesn't answer my question here.

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InquisitiveMind
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  • According to me, the level of the water in the pond should decrease. Why?, should the increased mass not displace the water back to it's original level. http://scienceprimer.com/buoyancy –  Jan 02 '17 at 17:04
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    @TáMéCeart I considered only one face of the coin, that is I only thought that the act of drinking water will reduce the water level of the pond, I did not think of its effects, Now I have understood it completely. – InquisitiveMind Jan 02 '17 at 17:09
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    In fact the top answer to the related question exactly answers yours. Just color the "stone" in the illustration blue and pretend it is made of water. – rob Jan 02 '17 at 17:09
  • @rob But the answers are different in my case the water level remains same, in their case the water level falls. – InquisitiveMind Jan 02 '17 at 17:10
  • But the method, which is explicit about the densities of the water in the lake and the object which enters/leaves the boat, is the same. – rob Jan 02 '17 at 17:20

2 Answers2

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The water level should stay exactly the same, by Archimedes' law: The boat will displace a volume of water that has the same weight as the boat. If you remove some water and put it in the boat, the boat will displace an additional amount of water that's exactly the same as the one you have removed.

Pirx
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When the man drinks some water from the pond, his weight increases and therefore the boat will sink further. The further sinking of the boat will displace the same volume of water in the pond as drunk by man. Therefore, there will be no change in the level of water in the pond.

InquisitiveMind
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