Why is ice always closed on water?

Water can freeze, which is a common occurrence in nature. Upon closer inspection, you may notice that the ice is always closed on the surface of the water. Winter in the cold north, on the surface of rivers or lakes often covered with a fairly thick layer of ice, even though the ice has melted in the early spring, it is still possible to see some ice floating along the water.

Because the water’s surface is in direct contact with the outside air, when the outside temperature is very low, the surface of the water begins to cool first. The density (density) of cold water becomes large, immediately sinking; while water density with relatively high temperatures at the bottom is relatively small, it emerges. The rising of the water like this is convection. However, water is a material that has a “weirdness” different from everything else. When the outside temperature is cold to 4 ° C, the density of water is greatest, convection of the water does not occur anymore. If the outside temperature continues to drop to 0 ° C, the surface water begins to freeze.

When water freezes, its volume increases to a tenth, thereby making the density of ice smaller than water. So, the ice always floats on the water. Because at that time, without convection, the surface was cold to 0 ° C, but the water at the bottom could still be kept at approximately 4 ° C. Due to this nature of water, people in the snow and snow season, still can puncture the ice on the river to fish.