Friday has arrived, and just in time for the fifth installment of "A Taste of Physics" —
and this time: how do I know that the temperature of the water at the bottom of the lake in the video is exactly 4 degrees?
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One of the fascinating properties of water is that at four degrees Celsius its density is at its highest, meaning it is also the heaviest per cubic centimeter.
Water above or below 4 degrees weighs less, and ice is lighter than liquid water.
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The freezing process of a lake consists of several stages:
- The water at the lake's surface cools from the air down to 4 degrees. At 4 degrees it becomes the heaviest and sinks to the bottom.
- The warmer water continues to rise to the surface, release heat, cool down to 4 degrees, and sink.
- Once all the water in the lake has reached 4 degrees, the upper layer continues to cool and begins to freeze.
- After a layer of ice has formed across the entire surface of the lake, the ice acts as an insulator that prevents the water beneath it from continuing to cool and freeze.
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During the thawing process, the reverse does not happen, because warm water does not sink. The lake simply melts gradually as heat penetrates slowly into the depths of the water over the summer months.
In the video: the thawing process of Lake Michigan
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