Water level

[turnkey4099]

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

 

[BTDT]

Need more info. Does this block happen to be tied around the neck of the guy who started the "will it take off thread"?

 

[Opti-Mist]

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.

 

[Tom_Veatch]

Need more info. Does this block happen to be tied around the neck of the guy who started the "will it take off thread"?

Gawd, I hope so!!!! (Water level will fall.)

 

[Doc_Bob]

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

Compared to what? before the boat arrived to drop the block?
Bob

 

[Jethro]

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.

 

[HTWT]

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.

 

[RayH]

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.

Yea, what he said.

 

[shaley]

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

 

[Jethro]

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.

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

 

[Knotbored]

This reminds me of a canary on a perch in a balloon on a scale-canary flies around-does the weight of the whole balloon assembly change ?

 

[SPYDERLK]

This reminds me of a canary on a perch in a balloon on a scale-canary flies around-does the weight of the whole balloon assembly change ?

If the balloon is sealed no. If not yes. A fly flying in a car does not increase the cars weight unless it lands. It does, however, increase the cars effective mass all the time -- but in a sorta cushy way when its airborne.
Larry

 

[daTeacha]

Archimedes principle states that an object immersed in a fluid will displace an amount of the fluid equal to the mass of the object or the volume of the object, whichever occurs first.

The block when in the boat helps the boat displace an amount of water equal to the mass of the block. When in the water, it only displaces water equal to the volume of the block which, by virtue of the fact that the block is more dense than water, will be less than the amount displaced when the block is in the boat. Ergo, the water level in the lake is lower when the block is in the water.

 

[BTDT]

I have to keep telling myself--This is a tractor forum, this is a tractor forum, this is...

 

[Tig]

Ok, so instead of a boat he uses a tractor with a FEL and then the EPA shows up to to investigate why he is filling in wetlands.

 

[turnkey4099]

Ok, so instead of a boat he uses a tractor with a FEL and then the EPA shows up to to investigate why he is filling in wetlands.

Well, if he uses the FEL to bury the plane and the conveyor as part of the fill, I am sure the EPA would approve.

Harry K

 

[greenedeere]

Good answer.