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我们知道,正常情况下物质是热胀冷缩的,所以温度越高,物质的密度越小。但也有一些例外情况,如水在0℃～4℃之间是热缩冷胀的,人们把这种现象叫做反常膨胀。设想把一定质量的水从0℃加热到10℃,水的体积是先减小后增大的,4℃是转折点,此时体积最小,密度最大。水的这种奇异特性很容易在自然界中看到,如冬天河塘里的水结冰时,总是从水面开始的。也就是说首先是河面的水温降到0℃,下面的水温则高于0℃,从上向下温度逐渐升高,河底温
We know that under normal circumstances the material is hot and cold, so the higher the temperature, the lower the density of the material. However, there are some exceptions, such as the water between 0 °C ~ 4 °C is shrinking cold expansion, people call this phenomenon abnormal expansion. Imagine heating a certain amount of water from 0°C to 10°C. The volume of water decreases first and then increases. 4°C is the turning point. At this time, the volume is the smallest and the density is the highest. This strange characteristic of water can be easily seen in nature. For example, when the water in a winter pond is frozen, it always starts from the water surface. In other words, first, the water temperature of the river surface drops to 0°C, the water temperature below it is higher than 0°C, and the temperature gradually increases from the top to the bottom.