Global Warming

[Scott S]

I am still arguing Steve and Bo

http://van.physics.uiuc.edu/qa/listing.php?id=1650

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

Question

Assume there is an ice cube in a glass of water. When the ice cube melts, will the water level have risen, fallen, or remained the same? Why?

Asked by: Hugo Polichemi

Answer

Lets see now. Some intuitive center in my brain is screaming 'it will remain the same', but we will try to think it over.

In the first state, we have an ice cube of mass m floating in the water. If it is floating (in equilibrium), it will have to displace enough water to support its weight. How much is that? It is just Volume = m/d , where m is the mass of the ice cube, and d is the density of water.

In the second state, where the ice has melted, it turns into water of volume.... Volume = m/d! exactly the same volume as it displaced before. So the added volume is the same, so the level of the water will not change.

As a matter of fact, as long as objects are floating (i.e. they don't rest on the bottom) they displace enough water to support their mass. Since by turning from solid to liquid, the mass of water does not change (well, maybe it does, due to mass-energy equivalence, but that's _really_ negligible) it will keep displacing the same amount of water.

However, note that this may not apply to everything. If you had solid alcohol floating in water, when it melts, the level would drop, because water and alcohol mix at the molecular level; i.e. water filling spaces among alcohol molecules.

Answered by: Yasar Safkan, Ph.D., Sofware Engineer, Noktalar A.S., Istanbul, Turkey

Am I still wrong?

I love this stuff too.

Scott S

[VRM]

Ok, Scott - I went back and figured out what the problem is.

You are correct regarding a freshwater ice cube in a glass of fresh water with equal densities for both.

I am correct regarding a floating ice cube (or iceberg) with any degree of fresh water in the ocean raising the sea level more than it displaces.

My mistake was in applying what I know of ice bouyancy/density of icebergs to a freshwater ice cube in a fresh water glass (not many of us drink glasses of saltwater). Roughly 11% remains above water whereas an ice cube of equal density to the water in a glass has a little less than 9% above water.

Sorry about that...Does it make more sense now?

I suppose that is what I get for doing my own homework rather than just copying and pasting someone elses...

Steve

[Scott S]

Originally Posted by VRM

I suppose that is what I get for doing my own homework rather than just copying and pasting someone elses...

Steve

I tried in my own words to prove it, I then had to resort to someone else's.

I think I mentioned in an earlier post about averaging the ice. The experiment would be the same if you used both sea water and sea ice. The problem would be to determine how much freshwater ice/snow is on top of the sea ice.

I am wondering if the average salinity of the oceans is decreasing, that would mean that the fresh water ice on land is melting at an increased rate wouldn't it?

Scott S