Technical question....

[iranu]

Cause and effect folks. The volume changes will only be due to changes in density of the water once the icecube has melted. The change in density depends on the temperature of the water to start with and how much mass the icecube has is in relation to the mass of water.

This density change is incy wincy in a normal pint glass/normal sized icecube - see link in my previous post, and for all intense purposes can be assumed to be zero.

As far as ice caps melting and all that, the model of icecubes melting in a glass of water is a little too simplistic.

[Nick]

Erm, so whats the answer... is the water level less, the same or higher?

[herulach]

As a physists you should be ashamed

Us metallurgists have to understand phase changes, thermodynamics (eugh) etc. We won't even get into the "triple point" for water, i.e. a 3 phases (gas, liquid, solid) existing in equilibrium at about 0.2°C iirc or the phenomenon of undercooling.

I'm a theoretical physicist, well, at least i will be in a year, bloody 4 year courses, so i can be excused not being able to do actual experiments, i do however know how to apply the ideal gas theory that gives you the triple point to work out the behaivour of magnets and electrons in metals, although that has little bearing on the problem a bit of boasting might help to soothe my ego a bit

[mike_w]

Erm, so whats the answer... is the water level less, the same or higher?

I still stand by the same. And as for the icecaps, if memory serves, we need to be more worried about the effects of thermal expansion on the sea so far as flooding/rising sea levels go.

[herulach]

The icecaps is because wuite a lot of it, i.e most of greenland is on land, so melting = higher sea levels.

[chriswood_7]

I think there are so many assumptions to be made in this, one being how much of the ice cube is submerged. I suppose if you think of it in the way that if you were to fill the glass up and then make two ice cubes out of that water then it will return to its original level once it is fully melted. However, if you were to put two ice cubes in the water and fill up the glass to the top, as the ice melted it would overflow by the amount that wasnt submerged under the water?

So maybe we could say that it will stay the same as the difference in densities make it quite difficult to actually determine? I suppose that if you have two volumes of water, both with different densities maybe you could calculate the density of the ice cube if you knew its exact dimensions and mass?

[mike_w]

I think there are so many assumptions to be made in this, one being how much of the ice cube is submerged. I suppose if you think of it in the way that if you were to fill the glass up and then make two ice cubes out of that water then it will return to its original level once it is fully melted. However, if you were to put two ice cubes in the water and fill up the glass to the top, as the ice melted it would overflow by the amount that wasnt submerged under the water?

So maybe we could say that it will stay the same as the difference in densities make it quite difficult to actually determine? I suppose that if you have two volumes of water, both with different densities maybe you could calculate the density of the ice cube if you knew its exact dimensions and mass?

If my thinking is right, how much of the ice cube is submerged, and the ice cube's density, is irrelevant. I think tiggerai had the best explanation. If you have 10ml of water and freeze it, it is now more than 10ml. However, it still has the same mass/weight as 10ml of water, so it displaces 10ml of water. When it melts, it becomes 10ml of water - which is the amount that it displaced. Therefore, there is no change in water level.

[Nick]

Ahh yes, but if I had 10ml of lead, that'd displace the same volume of water as 10ml of ice, in fact, it'd displace more as it'd be totally submerged, so it's not a question of density...

[chriswood_7]

Im sure 10ml of water doesnt increase when its frozen, its only a matter of volume that increases and hence density reduces. If you put the ice cube in a glass and measure the water level, that displacement will be equal to the volume submerged under the water, which could also be equal to the difference in densities..therefore the water would stay the same?

[Byatt]

Im sure 10ml of water doesnt increase when its frozen, its only a matter of volume that increases and hence density reduces. If you put the ice cube in a glass and measure the water level, that displacement will be equal to the volume submerged under the water, which could also be equal to the difference in densities..therefore the water would stay the same?

Welcome to the thread. We got to this conclusion on page 1!

[mike_w]

Ahh yes, but if I had 10ml of lead, that'd displace the same volume of water as 10ml of ice, in fact, it'd displace more as it'd be totally submerged, so it's not a question of density...

That's not the same. The water level stays the same with ice since that is frozen water i.e. the same compound, but lead is a different substance.

[chriswood_7]

i know thats what im kind of reiterating...

[Nox]

heh, this question came up in my A-level physics group, erm, 15 years ago.

The level stays the same, and you're correct about the poles thing - we only have to worry if the one that sits on land melts.

Nox

[chriswood_7]

What a great thread!

[Nox]

Ahh yes, but if I had 10ml of lead, that'd displace the same volume of water as 10ml of ice, in fact, it'd displace more as it'd be totally submerged, so it's not a question of density...

no, it would displace the same as 10ml of water, or 10 ml of water thats been frozen.

Nox

[mike_w]

The level stays the same, and you're correct about the poles thing - we only have to worry if the one that sits on land melts.

Of course, we should worry if either of the poles melt because of the poor little penguins and polar bears!

Logically, if any substance decreases in density when it freezes, and therefore floats in its liquid equivalent, the level of liquid should remain constant as the solid melts.