if heat rises, why do bodies of water freeze from the top down?

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If I had to guess, it’s because the temperature above the water is constantly colder than the water itself – but that is what I actually don’t understand.

If the surface temperate is extremely colder than the temperature of the water itself, wouldn’t the cold “sink” that much faster, making the warm water “rise” at an equivalent rate, and thus forcing more of the cold water to the bottom?

Maybe a better post for stupid questions, but I’m very curious what causes this – perhaps this just applies to air, and not water? And if that’s the case, then also why?

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Anonymous 0 Comments

Because ice is less dense than water so it floats to the top.

The idea of “heat rising” isn’t directly true. What is true is that less dense things rise above more dense things. And generally speaking, stuff becomes less dense when it gets hotter. This is most pronounced when it comes to gasses, but it *does* affect liquids too (and even solids, but that isn’t really meaningful for most things).

So cold water is likely to “sink” that is true, but ice floating is more important.

Fun fact, for really deep water (like the ocean) the pressure keeps ice from forming. Because ice needs to expand in order to freeze, which it can’t do when under such immense pressure.

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