Technical question....

[chriswood_7]

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.

Excellent conclusion...

Anyone answer why specific heat of air at constant pressure is higher than specific heat at constant volume?

[Nox]

I think you only have to worry if the ice cube is made of a different substance, and the molecules are sufficiantly small that they can go 'in between' the water molecules, which would then not raise the level much.

I'm not a physicist or chemist tho, so don't quote me.

Nox

[Nick]

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

Nox

How's that then? Some of the ice wouldn't be submerged, so it wouldn't be displacing any water.

[herulach]

How's that then? Some of the ice wouldn't be submerged, so it wouldn't be displacing any water.

Yes but to float it would need to displace its own weight, i.e 10ml worth of water

[Nick]

Ok, but weren't we talking about volume?

I mean, a 10ml lump of lead will displace the equivalent volume of water as ten mls of water, but a 10ml cube of ice won't, cos some of it is floating... or is is that the submerged part of the ice cube is equivalent to 10ml and the extra 'floaty' bit is the expanded part?

(well, obviously not the one bit that expands but I mean it's equivalent in volume tot he total expansion of the water when it freezes)

[yamangman]

Answer this one then - why does liquid freeze quicker the hotter it is?

[Nick]

Ahh, that's something to do with the latent heat of vaporisation... I think... but your question can wait until I've got an answer here... I've been waiting two days to see if I'm going to overflow my glass of Pimms!

[SilentDeath]

Ok, but weren't we talking about volume?

I mean, a 10ml lump of lead will displace the equivalent volume of water as ten mls of water, but a 10ml cube of ice won't, cos some of it is floating... or is is that the submerged part of the ice cube is equivalent to 10ml and the extra 'floaty' bit is the expanded part?

(well, obviously not the one bit that expands but I mean it's equivalent in volume tot he total expansion of the water when it freezes)

10ml of anything will always diplace 10ml of anything else exactly, assuming it is fully submerged - becuase they are the same volume and displacement is measured in volume.



The percentage of ice that floats is constant with the density ratio between the liquid and ice.

If the denity of ice was 4/5th that of water for example, then 1/5th would be above the waterlevel - I think, thats compleatly based on the last time I had a drink with ice in it + someone said ice was ~0.8g/cm3 vs water being 1g/cm3

[Tumble]

Ok, but weren't we talking about volume?

I mean, a 10ml lump of lead will displace the equivalent volume of water as ten mls of water, but a 10ml cube of ice won't, cos some of it is floating... or is is that the submerged part of the ice cube is equivalent to 10ml and the extra 'floaty' bit is the expanded part?

(well, obviously not the one bit that expands but I mean it's equivalent in volume tot he total expansion of the water when it freezes)

If you put a 500 tonne boat in a pond that's absolutely brimming, and catch ALL the water it squishes out, you'd have 500 tonnes of water in your catching thingummy... don't matter how much is sticking out the top, it'll still displace the same amount of water as it weighs - it's just a question of whether the object in the water is bouyant or not.

[mike_w]

Ok, but weren't we talking about volume?

I mean, a 10ml lump of lead will displace the equivalent volume of water as ten mls of water, but a 10ml cube of ice won't, cos some of it is floating... or is is that the submerged part of the ice cube is equivalent to 10ml and the extra 'floaty' bit is the expanded part?

(well, obviously not the one bit that expands but I mean it's equivalent in volume tot he total expansion of the water when it freezes)

An object floats when its mass is less than the mass of water it is displacing. In this case, ice is less dense than water, so it floats - the water it is displacing has greater mass/weighs more. As it reaches the top of the water, the water displaced decreases, until the mass of water displaced by the ice cube equals the mass of the ice cube.

If you have a 10ml cube of ice, it will be made of less than 10ml of water, since ice is less dense than water i.e. the water expands. However, if you have 10ml of water, then freeze it, it is now more than 10ml of ice. It still has the same mass as before, just more volume. So when you put it into the water, it will displace 10ml of water because the mass is the same as 10ml of water. It is not completely submerged because the ice cube itself is more than 10ml. If it were completely submerged, it would displace too much water.

I think that makes sense!

[iranu]

Archemedes principle - http://www.infoplease.com/ce6/sci/A0804583.html

Answer

http://www.physlink.com/Education/AskExperts/ae389.cfm

http://van.hep.uiuc.edu/van/qa/secti...0510173719.htm

Hot water freezing in a shorter time than cold water - true

http://math.ucr.edu/home/baez/physic...hot_water.html

http://www.picotech.com/experiments/...t/results.html

[herulach]

If you put a 500 tonne boat in a pond that's absolutely brimming, and catch ALL the water it squishes out, you'd have 500 tonnes of water in your catching thingummy... don't matter how much is sticking out the top, it'll still displace the same amount of water as it weighs - it's just a question of whether the object in the water is bouyant or not.

Not true, if it sinks then it doesnt displace as much as it weighs, thats how bouyancy works

Answer this one then - why does liquid freeze quicker the hotter it is?

Where the hell did you here that? It might cool faster in contact with the same temperature resevoir, but thats because cooling rate is proportionally to temperature difference, so assuming it was a proper resevoir it would eventually end up on the same curve as something at a lower temp.

[Nick]

Mike, ta!

Iranu, ta!

Everyone else, ta!

Pimms is now served!

[SilentDeath]

Not true, if it sinks then it doesnt displace as much as it weighs, thats how bouyancy works

Where the hell did you here that? It might cool faster in contact with the same temperature resevoir, but thats because cooling rate is proportionally to temperature difference, so assuming it was a proper resevoir it would eventually end up on the same curve as something at a lower temp.

Well boats generally float. If he wanted it to sink, he would have said large 500 ton sinking thingy that sinks, and doesnt float.

As for hot water freezing faster than cold water, iirc it becuase the hot water particles are more active and so cools more effienctly at first which allows the surface to cool quicker, or something...

[herulach]

Well boats generally float. If he wanted it to sink, he would have said large 500 ton sinking thingy that sinks, and doesnt float.

As for hot water freezing faster than cold water, iirc it becuase the hot water particles are more active and so cools more effienctly at first which allows the surface to cool quicker, or something...

I was meaning this bit:

don't matter how much is sticking out the top, it'll still displace the same amount of water as it weighs - it's just a question of whether the object in the water is bouyant or not.

although re reading it does make a little more sense in terms of boaty ness and floating, it was the last part that threw me.

And yes, hot water will cool quicker at first, it will not however freeze faster, its a completly reversible process, water that is at one temperature will behave the same (assuming pressure etc constant) regardless of its history.

[chriswood_7]

Anyone on the specific heat question?