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Things I don’t understand, Part 8

When matter gets warm, it expands.
When matter cools, it shrinks.
Simple, right? That’s because the molecules vibrate more at higher temperatures, so they need more space to do their little molecular disco (or whatever the kids are calling it these days).

Here’s the thing, though…

Water is exactly the opposite.
Water EXPANDS when it freezes, and it contracts when it melts.
I remember reading that the ratio is 9/10… in other words, nine buckets of water will freeze and expand to the equivalent of TEN buckets of ice.

So…. WHY is water different?

I don’t understand.
.

Comments 5

  1. John wrote:

    Hi,

    When water is busy being water, it’s got a really funky charge going, so all the little water molecules can do a lot of serious down-and-dirty cuddling and hugging while they boogie…

    but when the water slows down to become ice, it crystallises, so the water molecules (in an attempt to adapt to a new, more sedentary life, based on chilling out on the sofa watching the tube and eating potato chips) develop a need for their own space…

    which is why water molecules take up more room as ice.

    Posted 25 Jun 2007 at 9:19 am
  2. Janna wrote:

    John: This makes me wish I had actually paid attention in Chemistry class… If only I’d known about the “down-and-dirty cuddling” back then, I might have gotten more dates.

    Posted 25 Jun 2007 at 2:39 pm
  3. Lynda wrote:

    I like John’s answer.

    Posted 29 Jun 2007 at 3:24 pm
  4. John wrote:

    I never got any dates in Chemistry class – but it was an all-boys school and I always liked the idea of taking a girl on a date, so I guess I’m not too bothered.
    Years later, I got the chance to take a girl to 1742, and we ran around freaking out the locals with our crazy modern gadgets. We laughed and laughed…
    If you’re going to take someone on a date, you can do worse than 1742.

    Posted 29 Jun 2007 at 4:19 pm
  5. jabba wrote:

    Another fun fact is that this very property of water is thought to be the reason for the existence of life on Earth. If water froze like normal substances, the entire planet could freeze over relatively easily.

    This idea is one of the cornerstones of the Anthropic Principle, which tried to explain that the universe and all its forces are optimized for human life. Interestingly enough, this principle is now used by would-be philosophers on both sides of the Creation debate.

    Apologies for being dry. Drier still: http://en.wikipedia.org/wiki/Anthropic_principle

    Posted 23 Sep 2007 at 11:21 pm

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