Ice Cube

  • Thread starter chemical
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  • #1
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stuck in explaining this problem

A glass of water contains a large ice cube

the glass can hold no morw water

the ice is floating in the water

what will happen to the water level when the ice melts?
 

Answers and Replies

  • #3
Rog
20
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Originally posted by Guybrush Threepwood
the level will drop.
the ice has a density a bit lower than the water (that's why ice is floating).

http://www.its.caltech.edu/~atomic/snowcrystals/ice/ice.htm
I disagree. The ice cube is made wholly of water in a cryistaline form and therefore its mass although lower than liquid water would still diplace the same amount of water as is contained within the cube. if the cube melts the water from it will replace exactly the water that was originally displaced by the cube. therefore the level will remain the same.
 
  • #4
Njorl
Science Advisor
258
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Rog has it right. A floating object displaces its mass, a sunken one displaces its volume. Remember Archimedes.

Njorl
 
  • #5
Originally posted by Rog
I disagree. The ice cube is made wholly of water in a cryistaline form and therefore its mass although lower than liquid water would still diplace the same amount of water as is contained within the cube. if the cube melts the water from it will replace exactly the water that was originally displaced by the cube. therefore the level will remain the same.
Is a perfect ice cube is made of wholly crystaline water? Aside from bubbles or such trapped particles, (which I am discounting), does the surface of the cube remain as a solid, or is it in a dynamic process of changing it's state?
 
  • #6
462
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Originally posted by S = k log w
Is a perfect ice cube is made of wholly crystaline water? Aside from bubbles or such trapped particles, (which I am discounting), does the surface of the cube remain as a solid, or is it in a dynamic process of changing it's state?
It doesn't matter. Even if the ice cube was an ice bubble, the amount of water it displaces is identical [to the volume (melted) of the water contained in the ice].
 
  • #7
305
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I know the answer to this question! I did this question for my hw.

The answer is the water level will lower and then rise. I'm not sure at what temp, but water has a different density at certain temp. I think near 3 or 4 C, the density is lower than at other temp.
 
  • #8
Njorl
Science Advisor
258
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Originally posted by david90
I know the answer to this question! I did this question for my hw.

The answer is the water level will lower and then rise. I'm not sure at what temp, but water has a different density at certain temp. I think near 3 or 4 C, the density is lower than at other temp.
H20 does some strange things around its melting point, there is not realy enough information in the problem to allow for those small effects. You would need to know the starting temperature of the water, and the ice, and their masses etc. If the thermal expansion coefficient of liquid water were monotonic, you could do what you say, but water is at it's maximum density at 4 degrees C I believe. Heat it or cool it from that point and it expands.

Njorl
 

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