Water level

   / Water level #1  
T

turnkey4099

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Apologies if this has been posted here before. I thought of adding it to the "will it take off" thread but that is getting a bit long.

A man is on a boat in a small pond. There is a concret block in the boat. He rows out to the middle and drops the block overboard. Does the pond water level rise or lower? Yes, the change would by almost undectectable but...

Harry K
 
   / Water level #2  
Need more info. Does this block happen to be tied around the neck of the guy who started the "will it take off thread"?
 
   / Water level #3  
The displaced weight will be effectively reduced as the block which was supported by the boat will now sink to the bottom and displace some sediment on the bottom as well as some water with the part not immersed in sediment. If I were a lawyer I could have said all this with so many more words that no one would be able to follow the train of thought. Assuming, of course, that it stays on track.
 
   / Water level #4  
BTDT said:
Need more info. Does this block happen to be tied around the neck of the guy who started the "will it take off thread"?
Click to expand...

Gawd, I hope so!!!!:D (Water level will fall.)
 
   / Water level #5  
turnkey4099 said:
A man is on a boat in a small pond. There is a concret block in the boat. He rows out to the middle and drops the block overboard. Does the pond water level rise or lower? Yes, the change would by almost undectectable but...

Harry K
Click to expand...

Compared to what? before the boat arrived to drop the block?
Bob
 
   / Water level #6  
I assume you are comparing the water level with the boat in the water in both instances. dropping the block in the water from shore would raise the waer level. However, the boat would displace more water with the weight of the block in it that it would with out it. So, we have to determine if the weight of the block in the boat would displace more water by placing more surface area of the boat in the water than the area of the block itself would. This sounds like a job for mythbusters.
 
   / Water level #7  
The water level will fall. If the block weighed 1000lb. and had a volume of 1 cubic foot. It would displace the volume of 1000 lb. of water (about 16 cu. ft.) while in the boat, but when it is droped in the water it will desplace only 1 cu. ft. and the pond will fall by a volume of (16-1) 15 cu.ft.
 
   / Water level #8  
HTWT said:
The water level will fall. If the block weighed 1000lb. and had a volume of 1 cubic foot. It would displace the volume of 1000 lb. of water (about 16 cu. ft.) while in the boat, but when it is droped in the water it will desplace only 1 cu. ft. and the pond will fall by a volume of (16-1) 15 cu.ft.
Click to expand...

Yea, what he said.
 
   / Water level #9  
I think Tom has it right. When the block is in the boat it is displacing its weight in water. F_bouyancy = Gamma * Volume
Gama is a materials specfic weight.
When the block is in the water it is displacing its volume. Concrete gama is greater than water so less volume. 148Lbs per qubic ft vs 62.4
 
   / Water level #10  
HTWT said:
The water level will fall. If the block weighed 1000lb. and had a volume of 1 cubic foot. It would displace the volume of 1000 lb. of water (about 16 cu. ft.) while in the boat, but when it is droped in the water it will desplace only 1 cu. ft. and the pond will fall by a volume of (16-1) 15 cu.ft.
Click to expand...

There you have it. You put the science to my logic. Thanks.
 
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