# Thread: Technical question....

1. ## Technical question....

Here's one for the scientific minded amongst you.

If I place two ice cubes in a glass of water and measure the level of the water on the side of the glass, wil the water level be higher, lower or the same once the ice cubes have melted.

For the sake of the pedants, no evaporation occurs during this time.

Well?

2. Depends on the size of the glass.

If we take the fact that Ice Cubes are 1/3rd larger then the water that contains them.

And assume that the icecubes are a perfect fit in the base of the glass, i.e. no gaps around them.

The water level will be lower at the end/

3. The same, because of the displacement of weight, not the amount of water

(I think, please don't flame me if i'm wrong)

4. Originally Posted by Dougal
If we take the fact that Ice Cubes are 1/3rd larger then the water that contains them.
That 1/3rd wil be outside of the water, so not effecting the water level.

Tiggerai got it right (I think )

5. Size of the glass, size of the ice cubes and the amount of water in total is surely irrelevant?

What matters is the volume of the ice cube and how much water it holds, yes?

See, my thinking is that it's all to do with volume and density.

Now if an ice cube holds x amount of water, but is less dense than water, is the amount of water it displaces equal, less or more than the amount of water that the ice cube holds?

6. Originally Posted by Nick
Size of the glass, size of the ice cubes and the amount of water in total is surely irrelevant?

What matters is the volume of the ice cube and how much water it holds, yes?

See, my thinking is that it's all to do with volume and density.

Now if an ice cube holds x amount of water, but is less dense than water, is the amount of water it displaces equal, less or more than the amount of water that the ice cube holds?
It displaces the same volume of water that the ice cube holds (once melted), as it's weight that effects it, not volume.

7. That's what I was going to say.

8. The water level will be higher after they have melted.
I could try to bother to work out the maths etc which will be quite hard as i'm p1ssed, or could go for the alternative way of thinking.

All of the global warming peps seem to think that melting the ice caps will raise the sea level.

My money's on them being right
So I guess while as ice some of the mass is above water, that more than makes up for the lower density

9. Ice unlike most solids, is less dense than liquid water = why it floats.

As ice is still water, it doesnt matter if there is mass above the liquid, as its still water, so the level would be marked at the top of the ice - which will always be on the top - with any quantity/ratio or shape of ice.

The level will be lower once it has melted

As for icecaps, some of them are considerably higher than the waterlevel. Thats like saying will the level in a glass be higher after pouring in water from a glass full of melted ice.

10. Originally Posted by badass
The water level will be higher after they have melted.
I could try to bother to work out the maths etc which will be quite hard as i'm p1ssed, or could go for the alternative way of thinking.

All of the global warming peps seem to think that melting the ice caps will raise the sea level.

My money's on them being right
So I guess while as ice some of the mass is above water, that more than makes up for the lower density
Because those polar icecaps are floating, right?

Originally Posted by silentdeath
The level will be lower once it has melted
Only if (as you say) the initial level is measured at the top of the ice - otherwise explanations from tiggerai are spot on.

I misread the question.

Water level will be lower.

12. Note: in what I say, the water level is the level of liquid water, rather than the ice.

If ice floats in water, it must be less dense. Therefore, when it melts, it would become more dense, and take up less mass. Assuming the ice was completely submerged, the water level would then drop. However, some of the ice is above the water level, so this would cause the water level to rise. Overall effect? I have no idea since I don't know how big the two factors are in relation to each other - it could go up or down, or just stay the same.

13. Nope, not measuring the level of the ice here, we're measuring the level of the water... Obviously, when you drop a couple of ice cubes in a glass of water, the water level rises a bit... and the ice is of course floating a bit too... iirc, it's 1/10 of the cube that sticks out of the water due to its density...

Now, is the current levle of water going to be higher or lower or the same once the ice has melted?

And on the ice cap issue if the water level for the ice in the glass will stay the same then we've nothing to worry about with the North polar ice cap..... but we've a lot to worry about with the Southern polar ice cap as all that ice is sitting on land, not water... so none of that is displacing the equivalent (or not) volume of water...

14. With the north Ice cap only 2/3rds of it is below water

15. I still stand by the water level will be the same.

16. Originally Posted by Nick
Nope, not measuring the level of the ice here, we're measuring the level of the water... Obviously, when you drop a couple of ice cubes in a glass of water, the water level rises a bit... and the ice is of course floating a bit too... iirc, it's 1/10 of the cube that sticks out of the water due to its density...
Right then, this is likely to be wrong, but this is my attempt at an answer...

I'm best at this sort of thing using a general example. Assume we have an ice cube of 10 cubic centimetres. If 90% is submerged, then it has displaced 9 cubic centimetres of water. Therefore, in terms of mass, 10 cubic centimetres equals 9 cubic centimetres of water. This means that the volume of ice is 1 1/9 greater than the volume of water when masses are equal.

If the ice turns to water, then volume will be divided by 1 1/9. In this example, volume is 10 divided by 1 1/9, which is 9 cubic centimetres. The displacement was 9 cubic centimetres of water, which has now been replaced by 9 cubic centimetres water. Therefore, no change in water level.

Does anybody agree? Or am I completely wrong?

Edit: You can change the submergence level or volume of ice, and it still holds true - I've just used real numbers to make it easier!

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