十万个为什么·科学启蒙30篇（2）

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为什么冰块会浮在水面上？

Most solids sink in their own liquid form, but ice is a rare exception because it becomes less dense when frozen.
Water molecules form hexagonal crystals as they freeze, creating empty spaces that increase volume without adding mass.
This expansion makes solid ice about 9% less dense than liquid water, so it naturally rises to the surface.
If ice sank instead, lakes and oceans would freeze from the bottom up, making aquatic life nearly impossible in winter.
The floating layer of ice also acts like an insulating blanket, slowing further heat loss from the water below.
Scientists call this property 'anomalous expansion of water', and it’s essential for Earth’s climate and ecosystems.
You can observe this by freezing a plastic bottle full of water — it bulges or even cracks as ice forms.
Unlike most substances, water reaches its maximum density at 4°C, not at its freezing point.

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Unlike most substances, water reaches its maximum density at 4°C, not at its freezing point. 与大多数物质不同，水在4°C时密度最大，而非在冰点。
Scientists call this property 'anomalous expansion of water', and it’s essential for Earth’s climate and ecosystems. 科学家称这一特性为‘水的反常膨胀’，对地球气候和生态系统至关重要。
Most solids sink in their own liquid form, but ice is a rare exception because it becomes less dense when frozen. 大多数固体会沉入自身的液态中，但冰是个罕见的例外，因为结冰后密度反而变小。

这篇中文题目最接近哪一句？为什么冰块会浮在水面上？一次学校运动会的通知一份超市购物清单

课文第一句的意思更接近？大多数固体会沉入自身的液态中，但冰是个罕见的例外，因为结冰后密度反而变小。今天学校放假了。请把窗户打开。

这一课主要在讲什么？（看英文标题） Why Do Ice Cubes Float in Water? How to cook noodles A maths worksheet

Unlike most substances, water reaches its maximum density at 4°C, not at its freezing point.

Unlike most substances, water reaches its maximum density at 4°C, not at its freezing point.

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用今天的表达，自己说一句。

例子：Unlike most substances, water reaches its maximum density at 4°C, not at its freezing point.