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 they water that is up higher is under less pressure. The water below has the weight of the water above pushing down and providing pressure.

Pressure and temperature are important for phase changes. If you increase the pressure you can decrease the temperature at which something will freeze or liquify.

Also water is a weird case where the frozen form is actually less dense than the liquid form. This is very, very rare. But it does apply to water. So once water freezes it will float to the top.

Also the cold is usually coming in via the air, which will be at the surface of the water.

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