Ice Diving question

[Warren_L]

I was recently ice diving and was discussing the amount of weight we needed to move the block of ice we cut to access the water. I'm pretty sure I know the answer, but have run into some "disagreements" with a few people. This is really just basic physics, but I thought I would pose this to the board if anyone is actually inclined to do the calculations.

1) How much additional weight is required to start to sink a block of freshwater ice that is a 10 foot equilateral triangle that is 8 inches thick?

2) Why does ice float?

Surprisingly, I've run into quite a few different explanations.....

 

[Big-t-2538]

Ha...I already did the math...

233 pounds to sink the ice...why...water is less dense in it's solid state than it is in it's liquid state.

 

[Marvintpa]

Due to the differing densities of the ice block involved I'm not sure the math is entirely that simple. Towards the bottom it was quite dense but towards the surface it was not nearly so.

Could you please share your figures with us?

 

[gfisher4792]

When water molecules freeze, they form up into a crystalline lattice kind of structure, which increases the space between the individual molecules, as compared to the space between them when in a liquid state, thus lowering density. Compare this to all (I believe) other liquids which become denser when they freeze/solidify.

 

[Big-t-2538]

Due to the differing densities of the ice block involved I'm not sure the math is entirely that simple. Towards the bottom it was quite dense but towards the surface it was not nearly so.

Could you please share your figures with us?

Certainly...

Density of ice = 57.25 lb/cu. ft.
Density of Water = 64.43 lb/cu. ft

The difference in density would be 64.43-57.25...or 7.18 lbs/cu. ft.

Surface area of triangle = 0.5*base*height. Base = 10ft. Height = 8.66 ft.
Thus SA ~= 43.3 sq. ft.

Volume of Triangle = Thickness * SA. T = 8 inches...or (8/12) 0.75 ft.

Thus total volume = 0.75ft * 43.3sq.ft. ~= 32.475 cu. ft.

Now...7.18lbs/cu.ft * 32.475cu.ft would be the amount of weight needed to sink the ice. This is approximately 233 pounds.

 

[Big-t-2538]

Compare this to all (I believe) other liquids which become denser when they freeze/solidify.

Negative...rubber exhibits the same odd solidification behavior.

 

[gfisher4792]

I figured that there'd be another odd one or two I didn't know about. Thanks!

 

[Big-t-2538]

Those are the only two that I know of off hand....I seem to remember there being a third, but that might have been alcohol influenced.

 

[rkr3000]

I would use the ice to keep my beer cold.

 

[rkr3000]

I wouid use the ice to keep the beer cold. After the dive of course! haven't been ice diving yet but hope to .