It's getting windier. - Page 9

AndrewJ · 09-01-2005, 11:59

Okay no worries.

SMHarman · 09-01-2005, 14:14

Quote:

Originally Posted by ianathuth

I started the thread because the wind was howling outside my study window and I have the distinct impression that the past few years have seen the weather getting windier and windier. Watching TV over the past couple of weeks has shown us the enormous forces of Mother Nature with many places wiped out by the Tsunami. This led to a few searches on Google which came up with things like a large increase in sea level being likely due to global warming and other factors. Vast icebergs breaking away from Antarctica have been in the news for the past couple of years. Animal life is being affected. All in all the starting point for discussion on what can be a fascinating and thought provoking subject.

So the howling wind prompted the thread but, as expected, it quickly went onto other aspects of Mother Nature which could all be contributors to producing this wind.

Another wind that is considerably up at the moment is the Atlantic Jetstream. My flight to Chicago at Christmas took 70 mins longer due to the Jetstream headwind, and the return, 60 mins less as a result. Thats a lot of extra push the Jetstream is giving it at the moment.

Theodoric · 09-01-2005, 19:38

Quote:

Originally Posted by JohnHorb

...disregarding the effect of changes in density, which I suspect is what nffc was referring to. All a bit acedemic though, as the main danger is from melting ice which is currently ON LAND.

I know that at first sight it seems like it should, but in actual fact, the changes in density don't make any difference. The ice contains exactly enough water, when it melts, to fill the space that the ice occupies in the water; no more, no less.

Even if the ice has drifted south to warmer water before it started melting it still wouldn't make any difference. Consider the ice at 0C and the water at 20C. The ice contains the same weight of water as that that was in the "hole" it makes. Assume it now melts very rapidly. Initially, as the melt water is at 0C, it will be a little smaller in volume than the hole. However, when it warms up to 20C it will expand exactly enough to fill the "hole", so the water level will remain the same.

09-01-2005, 20:30

Hope you're all watching C4 right now!

nffc · 09-01-2005, 20:43

Quote:

Originally Posted by Theodoric

I know that at first sight it seems like it should, but in actual fact, the changes in density don't make any difference. The ice contains exactly enough water, when it melts, to fill the space that the ice occupies in the water; no more, no less.

Even if the ice has drifted south to warmer water before it started melting it still wouldn't make any difference. Consider the ice at 0C and the water at 20C. The ice contains the same weight of water as that that was in the "hole" it makes. Assume it now melts very rapidly. Initially, as the melt water is at 0C, it will be a little smaller in volume than the hole. However, when it warms up to 20C it will expand exactly enough to fill the "hole", so the water level will remain the same.

Density of ice = 0.931 gcm^-3
Density of water = 1 gcm^-3

Let's say there was 1 mol of water molecules, that's 6.02x10(23) water molecules, and has a mass of 18g.

Density = mass / volume so the volume in the solid state will be 18/0.931 = 19.33 ml
In the liquid state the same water will have a volume of 18 ml.

The density of the water will remain constant whilst the water remains in one state.

So your argument that the water somehow expands to fill the space is fundamentally flawed. How would it happen?

09-01-2005, 20:48

??? Not sure what you are saiyng here. If the volume in the solid state is 19.33ml, and in the liquid state is 18ml, surely all that means is that 1,33 ml will be above water when the ice is floating?

Shaun · 09-01-2005, 20:51

Quote:

Originally Posted by nffc

The density of the water will remain constant whilst the water remains in one state.

That isn't the case, waters maximum density is at 4 degrees C, either side of that it is less dense. Think about the hydrogen bonds that are involved and what they do to the shape of the solid crystal and the bonds involved in the liquid. It is these bonds that also give water a higher than expected boiling point.

nffc · 09-01-2005, 20:54

Quote:

Originally Posted by JohnHorb

??? Not sure what you are saiyng here. If the volume in the solid state is 19.33ml, and in the liquid state is 18ml, surely all that means is that 1,33 ml will be above water when the ice is floating?

No, it means the volume of water will decrease by 1.33ml for every 18g of ice that melts.

(which is an appreciable volume and will have a marked decrease for massive glaciers)

BBKing · 09-01-2005, 21:16

Quote:

The density of the water will remain constant whilst the water remains in one state.

This is an incorrect statement - 'fundamentally flawed', in fact.

http://www.simetric.co.uk/si_water.htm

Key quote:

Quote:

The density of pure water is a constant at a particular temperature, and does not depend on the size of the sample. That is, it is an intensive property. The density of water varies with temperature and impurities.

It's perfectly obvious that melting sea ice will not cause a rise in sea levels, just as it's perfectly obvious that melting land ice *will* cause a rise in sea levels.

09-01-2005, 21:48

Quote:

Originally Posted by BBKing

This is an incorrect statement - 'fundamentally flawed', in fact.

http://www.simetric.co.uk/si_water.htm

Key quote:

It's perfectly obvious that melting sea ice will not cause a rise in sea levels, just as it's perfectly obvious that melting land ice *will* cause a rise in sea levels.

thankyou for summing up so concisely

Condolences to those who have lost their loved ones, during the recent storms across northern europe, by the way ..

ian@huth · 09-01-2005, 21:56

Quote:

Originally Posted by nffc

Density of ice = 0.931 gcm^-3
Density of water = 1 gcm^-3

Depends on what type of ice you are talking about and temperature. http://www.lsbu.ac.uk/water/phase.html

Raistlin · 09-01-2005, 22:57

WoW! What have I started with all this Science Stuff

nffc · 09-01-2005, 22:58

Quote:

Originally Posted by Raistlin

WoW! What have I started with all this Science Stuff

No idea but I have exams next week and this is sadly more interesting.

Raistlin · 09-01-2005, 23:36

Quote:

Originally Posted by nffc

No idea but I have exams next week and this is sadly more interesting.

ian@huth · 10-01-2005, 00:22

Bloody wind. It calmed down today but now it's picked up again and blowing quite strong.

It's bin day tomorrow for the recycling wheelie bin which is mostly full of paper, card and plastic bottles. Bins have to be out by 6:00 am and sometimes it's not much after then when they are emptied.

You can guess what's just happened. Crash, look out of window, bin on its side, contents blowing all over the place. Not just ours though so it's quite messy out there.