MadSci Network: Physics

Re: Does water under pressure have a lower freezing point then water at normal

Date: Tue Dec 15 06:56:38 1998
Posted By: Bob Novak, Other (pls. specify below), Sr Process Research Engineer, Carpenter Technology
Area of science: Physics
ID: 912300014.Ph

Hello Donald,

Yes it does.  The classic example taught in school is an ice skate.  The 
pressure from the skate causes a thin film of ice to melt.  The liquid 
water layer reduces the friction so the skater can go faster.

This is something that is peculiar to water.  If you look up the density of 
water vs temperature, you will find the maximum density is at 4 degrees 
centigrade.  Solid water or ice increases in volume as it gets colder.  
This is the reason that antifreeze is used in heating systems.  If the 
water solidifies the expansion in volume will burst the pipes.

The effect of pressure is much greater when water boils.  This is because  
the change in volume upon vaporization is much greater than the change in 
volume during solidification.  Auto cooling systems use pressure to operate 
at higher temperatures than are possible at atmospheric pressure.

Now that the weather is getting more like December here in the NorthEast, 
you might want to go try a physics experiment.  Get some ice skates and 
check it out!

Happy Holidays
Bob Novak
Specialist, Process R&D
Carpenter Technology

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