Cream Soda Physics & Diving

[Rick Inman]

If a liquid under pressure is cooled, then the pressure is released, the freezing point is also changed, at least temporarily.

OK, but, How?

 

[jonnythan]

It has nothing to do with the freezing point of the liquid changing.. it's the cooling effect of releasing the pressure.

 

[Firefyter]

It has nothing to do with the freezing point of the liquid changing.. it's the cooling effect of releasing the pressure.

jonnythan is right, I was having a brain f@#t. The freezing point is not changed, the sudden release of the pressure lowers the temperature of the liquid to it's freezing point. Sometimes I have a problem putting thoughts into words, thanks for the clarification.

 

[Fly N Dive]

so why does it work with bottled water that is under very little pressure?

 

[DepartureDiver]

It is more proper to talk about a melting point instead of a freezing point since a solid will always melt at the same temperature, but not necessarily freeze at the same temperature. The liquid was supercooled. The reason it froze upon the release of the pressure was the CO2 bubbles that started coming out of solution. This created nuclei for the crystallization process to start occurring.

 

[Mako Mark]

Does this have anything to do with why ice forms on the top of the lake first?

I believe that ice forms on top of the lake because of the contact with cold air. It stays there because ice is less dense than liquid water and therefore floats, which is a good thing as if it were to sink, it would lead to a feedback effect that would ultimately create a snowball earth and therefore preclude life on our little planet.

 

[jonnythan]

Water gets less dense as it freezes. The pressure on the bottom of the lake is one of the reasons the ice forms on the top.

 

[DepartureDiver]

Water is densest at 4 degrees Celsius (39 degrees F) and will be at the bottm. This has to do with the shape of the hydrogen bonding. Therefore water at freezing (including ice) or just about freezing is less dense and will rise and be at the surface.

 

[Hank49]

Water is densest at 4 degrees Celsius (39 degrees F) and will be at the bottm. This has to do with the shape of the hydrogen bonding. Therefore water at freezing (including ice) or just about freezing is less dense and will rise and be at the surface.

How would this be true in a moving body of water that freezes, such as a river which is more or less always mixing? I think C Mark is correct in that the cold air freezes the water and therefore the surface gets colder first.

 

[SueMermaid]

Ecch. I hate cream soda.