[tonyarkles]

That’s the other bizarre thing about water/ice: most things expand as you heat them, but very few things expand as you cool them. Water has maximum density at 4C, so even before you freeze it it’s already starting to expand as you cool it.

[pi-e-sigma]

You have it backwards. Density is mass/volume so with the same mass when density increases the volume decreses

[tonyarkles]

You're right about how density works, but I don't have it backwards:

A given mass of water:

- At 20C is less dense/higher volume than water at 4C

- As you cool it the density increases and the water shrinks

- At 4C the water is now at maximum density and minimum volume

- As you continue cooling it from 4C, it starts expanding again

- At 3C the water is lower density than it was at 4C and is again expanding

- At 0C where the water starts to transition to a solid the volume expands significantly

I guess I wasn't clear that the expansion only starts again as you go from 4C -> 0C in the liquid phase.

[pi-e-sigma]

ah OK, I get your point :) It doesn't really matter though because water when liquid doesn't cause any problem when expanding or contracting, its level in a vessel will just slightly change. It's only the ice that can fuck up pipes etc