why does water freeze from the top sown?

Water freezes from the top down because of a property known as thermal stratification. When water cools down, it loses heat and its temperature drops. However, water is most dense at about 4°C (39.2°F). Below this temperature, as water continues to cool, it expands rather than contracting, which is opposite to how most substances behave. This expansion causes the colder water near the freezing point (0°C or 32°F) to become less dense than warmer water beneath it.

When a body of water is exposed to cold temperatures, the surface water starts to lose heat faster due to direct contact with the cold air and radiation losses. Once the surface water reaches 0°C, it will begin to freeze, forming a layer of ice on the top. The ice insulates the water below, slowing down the rate at which it cools. Therefore, the coldest water (and the one closest to freezing) is always at the top, and that’s where ice formation begins.

As the ice layer thickens, the trapped air pockets underneath it provide insulation, preventing the rest of the water from freezing as quickly. This process continues until either all the water freezes (if the temperature stays low enough for a sufficient period) or the ambient temperature rises above freezing again.

In summary, water freezes from the top down because the surface loses heat faster, becomes colder first, and forms ice, which then insulates the remaining water below.

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