Water density question.........

[Mafesto]

Scenario is you have a crane suspending a 1000 lb aluminum cube.
There is a scale giving constant weight readout.
As you lower it into the water, we all know that the weight decreases.
My question is how much.
How much does it weigh just below surface?
How much does it weigh 10' below surface?
How much does it weigh 100' below surface?

Do the ratio percentages change with different solids? (steel, rock etc)

 

[Idcatman3]

From just below down, it's weight does not change significantly. Water is incompressible (mostly) so it's density does not change significantly with the increased pressure.

for how much it decreases in weight when you put it in the water depends on how big it is, not how much it weighs. Is it a solid cube?

 

[Mafesto]

While the water density changes very little as depth increases,
atmospheric pressure increases greatly.

Does this increased pressure affect the weight (or boyancy) of a solid?

 

[Dam Dave]

its only the size of the object that matters, you will displace an amount of water equal to the cube,


will it float? depends

http://en.wikipedia.org/wiki/Buoyancy

 

[Idcatman3]

No. It would affect things if say it were an upside down box filled with air, because the air would compress as you went down, and more of the volume would be filled with water. If the entire volume is filled with something incompressible (aluminum) then the buoyancy does not change with depth.

Any solid underwater will always weigh:

original weight - (volume*density of water)

with appropriate conversions from mass to force.

edit: reply to Mafesto, not Dave.