Water is a substance that we are all too familiar with. It is ubiquitous and an integral part of life. People can live from day to day if they are only vegetarian or only eat salty foods, but no matter who they are, they cannot survive without water.
But perhaps it is because of the familiarity that people often ignore and ignore this interesting liquid.
Water always freezes from the top down.
The highlight in water is that they often freeze from the top down and then spread gradually down, unlike other substances, which freeze from the bottom up. A good example is in the rivers and lakes of temperate, temperate regions, where the climate is much colder in winter, almost all of which are completely frozen on the surface.
To explain this phenomenon, we need to understand the somewhat “weird” nature of water. When the weather is not too cold, or more specifically, when the temperature is above 4 degrees Celsius (39.2 degrees Fahrenheit), the water follows the normal physical rules such as hot expansion, cold contraction.
When the temperature is below 4 degrees Celsius, the nature of water changes 180 degrees, they expand when they are cold and they contract when they are hot.
However , when the temperature is below that 4 degrees Celsius, things are completely different. At this time, the nature of the water changes by 180 degrees, when it is cold, it expands and when it is hot, it contracts. If the temperature continues to decrease, the density continues to increase and the water (in the solid state) continues to expand. Their mass is inversely proportional to the volume.
That means, with the same amount of water, the solid state water will be lighter and float to the top, the heavier warm water molecules will sink to the bottom. Therefore, water always begins to freeze at the surface first.
In addition, ice is less dense than water due to the way it is made up of a hexagonal crystal structure. Each water molecule consists of two hydrogen atoms bonded to the bottom of an oxygen atom. As ice forms, the hydrogen atoms of one water molecule form weaker hydrogen bonds with the top of the oxygen atoms of two other water molecules.
In temperate or temperate regions, it is quite common for the lake surface to freeze.
The arrangement of water molecules in this model takes up more space than if they were randomly jumbled together (as is the case in liquid water). And because the same molecular mass takes up more space when frozen, ice is less dense than liquid water.
George D. Ashton’s Textbook of Lake and River Engineering says : “When a lake cools from above 4°C, the water at the surface loses heat, becomes denser, and sinks. This process continues until the surface water loses heat, becomes denser, and sinks. when all the water in the lake is at 4°C, when the density of the water is at its maximum.
If the temperature continues to cool further, a stable, lighter layer of water will appear at the surface. As this layer cools to its freezing point, ice begins to form on the surface of the lake.”