Re: PHYS-L Digest - 30 Nov 2001 to 1 Dec 2001 (#2001-473)

[Brian Whatcott <inet@INTELLISYS.NET>]

At 09:36 PM 12/1/01, E C Muehleison wrote:
> /snip/
> The density of water increases to a maximum at about 4 degrees Celsius.

Yes

>  As
> the temperature continues to decrease, the density decreases.

yes

> Hence ice
> floats in water.

No. Ice does float in water - but it is not a consequence of the  thermal
cubic expansivity of liquid water, which is 2.1E-4 per Kelvin above 4 degC
and a similar negative quantity between 0 and 4 degC.
 The relative density of ice is 0.92 which represents the step increase of
volume at freezing - whereby your water pipes split

> However, if one believes the volume versus temperature curve
> as shown in Hewitt, then one must believe that the density of hot (above 20
> degrees celsius) is less than that of ice.


I don't have Hewitt: I assume his graph depicts the density variations of
liquid water, which as I mentioned, are rather modest compared with the
freezing density discontinuity.

>  Why, then, does ice float in very
> hot, nearly boiling, water?

Because it is less dense than boiling water.



Brian Whatcott
  Altus OK                      Eureka!